研究者詳細 - 野沢　徹

論文 - 野沢　徹

分割表示 >> ／全件表示 67 件中 1 - 67 件目

Global Historical Reanalysis with a 60-km AGCM and Surface Pressure Observations: OCADA 査読

Masayoshi ISHII, Hirotaka KAMAHORI, Hisayuki KUBOTA, Masumi ZAIKI, Ryo MIZUTA, Hiroaki KAWASE, Masaya NOSAKA, Hiromasa YOSHIMURA, Naga OSHIMA, Eiki SHINDO, Hiroshi KOYAMA, Masato MORI, Shoji HIRAHARA, Yukiko IMADA, Kohei YOSHIDA, Toru NOZAWA, Tetsuya TAKEMI, Takashi MAKI, Akio NISHIMURA

Journal of the Meteorological Society of Japan. Ser. II 102 ( 2 ) 209 - 240 2024年3月

The Importance of Ocean Dynamical Feedback for Understanding the Impact of Mid-High-Latitude Warming on Tropical Precipitation Change 査読

Masakazu Yoshimori, Ayako Abe-Ouchi, Hiroaki Tatebe, Toru Nozawa, Akira Oka

JOURNAL OF CLIMATE 31 ( 6 ) 2417 - 2434 2018年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER METEOROLOGICAL SOC

It has been shown that asymmetric warming between the Northern and Southern Hemisphere extratropics induces a meridional displacement of tropical precipitation. This shift is believed to be due to the extra energy transported from the differentially heated hemisphere through changes in the Hadley circulation. Generally, the column-integrated energy flux in the mean meridional overturning circulation follows the direction of the upper, relatively dry branch, and tropical precipitation tends to be intensified in the hemisphere with greater warming. This framework was originally applied to simulations that did not include ocean dynamical feedback, but was recently extended to take the ocean heat transport change into account. In the current study, an atmosphere-ocean general circulation model applied with a regional nudging technique is used to investigate the impact of extratropical warming on tropical precipitation change under realistic future climate projections. It is shown that warming at latitudes poleward of 40 degrees causes the northward displacement of tropical precipitation from October to January. Warming at latitudes poleward of 60 degrees alone has a much smaller effect. This change in the tropical precipitation is largely explained by the atmospheric moisture transport caused by changes in the atmospheric circulation. The larger change in ocean heat transport near the equator, relative to the atmosphere, is consistent with the extended energy framework. The current study provides a complementary dynamical framework that highlights the importance of midlatitude atmospheric eddies and equatorial ocean upwelling, where the atmospheric eddy feedback modifies the Hadley circulation resulting in the northward migration of precipitation and the ocean dynamical feedback damps the northward migration from the equator.

DOI： 10.1175/JCLI-D-17-0402.1

Effect of retreating sea ice on Arctic cloud cover in simulated recent global warming 査読

Manabu Abe, Toru Nozawa, Tomoo Ogura, Kumiko Takata

ATMOSPHERIC CHEMISTRY AND PHYSICS 16 ( 22 ) 14343 - 14356 2016年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：COPERNICUS GESELLSCHAFT MBH

This study investigates the effect of sea ice reduction on Arctic cloud cover in historical simulations with the coupled atmosphere-ocean general circulation model MIROC5. Arctic sea ice has been substantially retreating since the 1980s, particularly in September, under simulated global warming conditions. The simulated sea ice reduction is consistent with satellite observations. On the other hand, Arctic cloud cover has been increasing in October, with about a 1-month lag behind the sea ice reduction. The delayed response leads to extensive sea ice reductions because the heat and moisture fluxes from the underlying open ocean into the atmosphere are enhanced. Sensitivity experiments with the atmospheric part of MIROC5 clearly show that sea ice reduction causes increases in cloud cover. Arctic cloud cover increases primarily in the lower troposphere, but it decreases in the near-surface layers just above the ocean; predominant temperature rises in these near-surface layers cause drying (i.e., decreases in relative humidity), despite increasing moisture flux. Cloud radiative forcing due to increases in cloud cover in autumn brings an increase in the surface downward longwave radiation (DLR) by approximately 40-60% compared to changes in clear-sky surface DLR in fall. These results suggest that an increase in Arctic cloud cover as a result of reduced sea ice coverage may bring further sea ice retreat and enhance the feedback processes of Arctic warming.

DOI： 10.5194/acp-16-14343-2016

Asymmetric impact of the physiological effect of carbon dioxide on hydrological responses to instantaneous negative and positive CO2 forcing 査読

Manabu Abe, Hideo Shiogama, Tokuta Yokohata, Seita Emori, Toru Nozawa

CLIMATE DYNAMICS 45 ( 7-8 ) 2181 - 2192 2015年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：SPRINGER

We conducted sensitivity experiments using a coupled atmosphere-ocean general circulation model to examine the asymmetry between the hydrological responses to instantaneous positive and negative CO2 forcing and the impact of the CO2 physiological effects (CDPEs) on these responses. This study focuses on the fast response occurring on time scales shorter than 1 year after imposing CO2 forcing. Experiments investigating the CO2 physiological effect show that the fast response of precipitation to positive CO2 forcing is a decrease in the global and annual mean, whereas that of negative forcing is an increase the global and annual mean precipitation. The fast global precipitation response to negative forcing is stronger than the response to positive forcing. In contrast, the experiments without the CDPE reveal similar magnitudes of the fast global precipitation responses to negative and positive CO2 forcing. Significant differences in the magnitudes of the fast precipitation response due to the CDPE are found in tropical regions such as the Amazon Basin, the Maritime Continents, and tropical Africa, where C3-type plants are common. The stomatal conductance of plant leaves is decreased by both positive and negative CO2 forcing, which suppress the transpiration from the leaves. Consequently, the CDPE enhances the asymmetry of the fast precipitation responses to positive and negative CO2 forcing. The asymmetric impact of CDPE requires a careful evaluation of future hydrological changes which is constrained by paleoclimate evidence.

DOI： 10.1007/s00382-014-2465-1

Temperature scaling pattern dependence on representative concentration pathway emission scenarios A Letter (vol 112, pg 535, 2012) 査読

Yasuhiro Ishizaki, Hideo Shiogama, Seita Emori, Tokuta Yokohata, Toru Nozawa, Tomoo Ogura, Manabu Abe, Masakazu Yoshimori, Kiyoshi Takahashi

CLIMATIC CHANGE 125 ( 2 ) 277 - 277 2014年7月

Validation of a Pattern Scaling Approach for Determining the Maximum Available Renewable Freshwater Resource 査読

Yasuhiro Ishizaki, Tokuta Yokohata, Seita Emori, Hideo Shiogama, Kiyoshi Takahashi, Naota Hanasaki, Toru Nozawa, Tomoo Ogura, Toshiyuki Nakaegawa, Masakazu Yoshimori, Ai Yoshida, Shigeru Watanabe

JOURNAL OF HYDROMETEOROLOGY 15 ( 1 ) 505 - 516 2014年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER METEOROLOGICAL SOC

A pattern scaling approach allows projection of regional climate changes under a wide range of emission scenarios. A basic assumption of this approach is that the spatial response pattern to global warming (scaling pattern) is the same for all emission scenarios. Precipitation minus evapotranspiration (PME) over land can be considered to be a measure of the maximum available renewable freshwater resource, and estimation of PME is fundamentally important for the assessment of water resources. The authors assessed the basic assumption of pattern scaling for PME by the use of five global climate models. A significant scenario dependency (SD) of the scaling pattern of PME was found over some regions. This SD of the scaling pattern of PME was mainly due to the SD and the nonlinear response of large-scale atmospheric and oceanic changes. When the SD of the scaling pattern of PME is significant in a target area, projections of the impact of climate change need to carefully take into consideration the SD. Although the SD of the anthropogenic aerosol scaling patterns tended to induce SDs of precipitation and evapotranspiration scaling patterns, the SDs of precipitation and evapotranspiration tended to cancel each other out. As a result, the SD of the PME scaling pattern tended to be insignificant over most regions where the SD of anthropogenic aerosol scaling patterns were significant. The authors could not find large impacts of land use change on PME scaling pattern, but the former may influence the latter on different time scales or spatial scales.

DOI： 10.1175/JHM-D-12-0114.1

Dependence of Precipitation Scaling Patterns on Emission Scenarios for Representative Concentration Pathways 査読

Yasuhiro Ishizaki, Hideo Shiogama, Seita Emori, Tokuta Yokohata, Toru Nozawa, Kiyoshi Takahashi, Tomoo Ogura, Masakazu Yoshimori, Tatsuya Nagashima

JOURNAL OF CLIMATE 26 ( 22 ) 8868 - 8879 2013年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER METEOROLOGICAL SOC

Pattern scaling is an efficient way to generate projections of regional climate change for various emission scenarios. This approach assumes that the spatial pattern of changes per degree of global warming (scaling pattern) is the same among emission scenarios. The hypothesis was tested for the scaling pattern of precipitation by focusing on the scenario dependence of aerosol scaling patterns. The scenario dependence of aerosol scaling patterns induced the scenario dependence of the surface shortwave radiation scaling pattern. The scenario dependence of the surface shortwave radiation scaling pattern over the ocean tended to induce the scenario dependence of evaporation scaling patterns. The scenario dependence of evaporation scaling patterns led to the scenario dependence of precipitation scaling patterns locally and downwind. Contrariwise, when the scenario dependence of aerosol scaling patterns occurred over land, the scenario dependence of surface shortwave radiation scaling patterns induced the scenario dependence of the scaling patterns of evaporation, surface longwave radiation, and sensible heat. Consequently, the scenario dependence of evaporation scaling patterns was smaller over land, and the scenario dependence of precipitation scaling patterns tended to be insignificant. Moreover, the scenario dependence of the southern annular mode and polar amplification caused some of the scenario dependence of precipitation scaling patterns. In this study, only one global climate mode was analyzed. In addition, sensitivity experiments that remove aerosol emissions from some regions or some kinds of aerosols are ideal to separate the impacts of aerosols. Thus, an analysis of the dependencies of precipitation scaling pattern among global climate models and the sensitivity experiments are required in future work.

DOI： 10.1175/JCLI-D-12-00540.1

On the linear additivity of climate forcing-response relationships at global and continental scales 査読

Hideo Shiogama, Daithi A. Stone, Tatsuya Nagashima, Toru Nozawa, Seita Emori

INTERNATIONAL JOURNAL OF CLIMATOLOGY 33 ( 11 ) 2542 - 2550 2013年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：WILEY

Within the context of the prediction, detection and attribution of climate change, a number of studies have explicitly or implicitly assumed that individual climate responses to individual forcing agents can be linearly added to obtain the total climate response to the sum of the forcing agents. This assumption of the linear additivity of forcing-response relationships' has been tested by previous studies, but it remains controversial whether linear additivity holds with all combinations of forcing agents, such as greenhouse gases plus indirect effects of anthropogenic aerosols' or greenhouse gases plus solar irradiance'. This study explored whether linear additivity holds in 5-year mean temperature/precipitation responses to various combinations of forcing agents in the 20th century and in a future-emissions scenario at global and continental scales. We used Model for Interdisciplinary Research on Climate version 3, which includes the first and second indirect effects of aerosols. The forcing factors considered were well-mixed greenhouse gases, the direct and indirect effects of sulphate and carbon aerosols, ozone, land-use changes, solar irradiance and volcanic aerosols (the latter three factors were specified only in the 20th-century runs). By performing and analysing an enormous matrix of forcing runs, we concluded that linear additivity holds in temperature responses for all of the combinations of forcing agents at the global and continental scales, but it breaks down for precipitation responses in certain cases of future projections.

DOI： 10.1002/joc.3607

Hindcast Prediction and Near-Future Projection of Tropical Cyclone Activity over the Western North Pacific Using CMIP5 Near-Term Experiments with MIROC 査読

Masato Mori, Masahide Kimoto, Masayoshi Ishii, Satoru Yokoi, Takashi Mochizuki, Yoshimitsu Chikamoto, Masahiro Watanabe, Toru Nozawa, Hiroaki Tatebe, Takashi T. Sakamoto, Yoshiki Komuro, Yukiko Imada, Hiroshi Koyama

JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN 91 ( 4 ) 431 - 452 2013年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：METEOROLOGICAL SOC JAPAN

In line with the experimental design for near-term climate prediction toward the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, we perform ensembles of initialized decadal hindcast and near-future projection using three versions of the coupled atmosphere ocean model MIROC. In the present study, we explore interannual and multiyear predictability of tropical cyclone (TC) activity in the western North Pacific (WNP) using the initialized hindcasts and examine global warming impacts on TC activity in the near-future on the basis of near-future projections up to 2035.The hindcasts of year-to-year variation in TC number capture the observed values reasonably well. Moreover, interannual variability of TC genesis and occurrence frequency associated with the El Nino Southern Oscillation are found to be predictable, mainly through better prediction of sea surface temperature (SST) and large-scale vorticity anomalies in the lower troposphere. These results indicate that the models can reproduce the major basic mechanisms that link TC genesis with large-scale circulation. Skillful prediction of TC number is likely difficult on multiyear timescales, at least based on our hindcasts, but through initializations, the three-year-mean hindcasts from 1998 onward reasonably capture observed major characteristics of TC activity associated with Pacific climate shift during the late 1990s.Near-future projections (2016-2035) suggest significant reductions (approximately 14%) in TC number, particularly over the western part of the WNP, even under scenarios in which projected global warming is less prominent than that at the end of this century. This reduction is likely due to the suppression of large-scale lower tropospheric vorticity and relative humidity and the enhancement of vertical wind shear. The projected SST exhibits a more pronounced warming over the eastern tropical Pacific than over the western region and accompanies the weakening of Walker circulation via redistribution of tropical convection activity, which appears to be responsible for the change in the large-scale fields in the WNP.

DOI： 10.2151/jmsj.2013-402

An overview of decadal climate predictability in a multi-model ensemble by climate model MIROC 査読

Yoshimitsu Chikamoto, Masahide Kimoto, Masayoshi Ishii, Takashi Mochizuki, Takashi T. Sakamoto, Hiroaki Tatebe, Yoshiki Komuro, Masahiro Watanabe, Toru Nozawa, Hideo Shiogama, Masato Mori, Sayaka Yasunaka, Yukiko Imada

CLIMATE DYNAMICS 40 ( 5-6 ) 1201 - 1222 2013年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：SPRINGER

Decadal climate predictability is examined in hindcast experiments by a multi-model ensemble using three versions of the coupled atmosphere-ocean model MIROC. In these hindcast experiments, initial conditions are obtained from an anomaly assimilation procedure using the observed oceanic temperature and salinity with prescribed natural and anthropogenic forcings on the basis of the historical data and future emission scenarios in the Intergovernmental Panel of Climate Change. Results of the multi-model ensemble in our hindcast experiments show that predictability of surface air temperature (SAT) anomalies on decadal timescales mostly originates from externally forced variability. Although the predictable component of internally generated variability has considerably smaller SAT variance than that of externally forced variability, ocean subsurface temperature variability has predictive skills over almost a decade, particularly in the North Pacific and the North Atlantic where dominant signals associated with Pacific decadal oscillation (PDO) and the Atlantic multidecadal oscillation (AMO) are observed. Initialization enhances the predictive skills of AMO and PDO indices and slightly improves those of global mean temperature anomalies. Improvement of these predictive skills in the multi-model ensemble is higher than that in a single-model ensemble.

DOI： 10.1007/s00382-012-1351-y

Regional impacts of sulfur and carbonaceous aerosols on precipitation scaling patterns in representative concentration pathways 査読

Yasuhiro Ishizaki, Hideo Shiogama, Seita Emori, Tokuta Yokohata, Toru Nozawa, Kiyoshi Takahashi, Tomoo Ogura, Masakazu Yoshimori, Tatsuya Nagashima

J Climate 2013年

Perturbed physics ensemble using the MIROC5 coupled atmosphere-ocean GCM without flux corrections: experimental design and results Parametric uncertainty of climate sensitivity 査読

Hideo Shiogama, Masahiro Watanabe, Masakazu Yoshimori, Tokuta Yokohata, Tomoo Ogura, James D. Annan, Julia C. Hargreaves, Manabu Abe, Youichi Kamae, Ryouta O'ishi, Rei Nobui, Seita Emori, Toru Nozawa, Ayako Abe-Ouchi, Masahide Kimoto

CLIMATE DYNAMICS 39 ( 12 ) 3041 - 3056 2012年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：SPRINGER

In this study, we constructed a perturbed physics ensemble (PPE) for the MIROC5 coupled atmosphere-ocean general circulation model (CGCM) to investigate the parametric uncertainty of climate sensitivity (CS). Previous studies of PPEs have mainly used the atmosphere-slab ocean models. A few PPE studies using a CGCM applied flux corrections, because perturbations in parameters can lead to large radiation imbalances at the top of the atmosphere and climate drifts. We developed a method to prevent climate drifts in PPE experiments using the MIROC5 CGCM without flux corrections. We simultaneously swept 10 parameters in atmosphere and surface schemes. The range of CS (estimated from our 35 ensemble members) was not wide (2.2-3.2 A degrees C). The shortwave cloud feedback related to changes in middle-level cloud albedo dominated the variations in the total feedback. We found three performance metrics for the present climate simulations of middle-level cloud albedo, precipitation, and ENSO amplitude that systematically relate to the variations in shortwave cloud feedback in this PPE.

DOI： 10.1007/s00382-012-1441-x

The contribution of anthropogenic forcings to regional changes in temperature during the last decade 査読

Nikolaos Christidis, Peter A. Stott, Francis W. Zwiers, Hideo Shiogama, Toru Nozawa

CLIMATE DYNAMICS 39 ( 6 ) 1259 - 1274 2012年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：SPRINGER

Regional distributions of the mean annual temperature in the 2000s are computed with and without the effect of anthropogenic influences on the climate in several sub-continental regions. Simulated global patterns of the temperature response to external forcings are regressed against observations using optimal fingerprinting. The global analysis provides constraints which are then used to construct the regional temperature distributions. A similar approach was also employed in previous work, but here the methodology is extended to examine changes in any region, including areas with a poor observational coverage that were omitted in the earlier study. Two different General Circulation Models (GCMs) are used in the analysis. Anthropogenic forcings are found to have at least quadrupled the likelihood of occurrence of a year warmer than the warmest year since 1900 in 23 out of the 24 regions. The temperature distributions computed with the two models are very similar. While a more detailed assessment of model dependencies remains to be made once additional suitable GCM simulations become available, the present study introduces the statistical methodology and demonstrates its first application. The derived information concerning the effect of human influences on the regional climate is useful for adaptation planning. Moreover, by pre-computing the change in the likelihood of exceeding a temperature threshold over a range of thresholds, this kind of analysis enables a near real-time assessment of the anthropogenic impact on the observed regional temperatures.

DOI： 10.1007/s00382-011-1184-0

MIROC4h-A New High-Resolution Atmosphere-Ocean Coupled General Circulation Model 査読

Takashi T. Sakamoto, Yoshiki Komuro, Teruyuki Nishimura, Masayoshi Ishii, Hiroaki Tatebe, Hideo Shiogama, Akira Hasegawa, Takahiro Toyoda, Masato Mori, Tatsuo Suzuki, Yukiko Imada, Toru Nozawa, Kumiko Takata, Takashi Mochizuki, Koji Ogochi, Seita Emori, Hiroyasu Hasumi, Masahide Kimoto

JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN 90 ( 3 ) 325 - 359 2012年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：METEOROLOGICAL SOC JAPAN

A new high-resolution atmosphere-ocean coupled general circulation model named MIROC4h has been developed, and its performance in a 120-year control experiment (including a 50-year spin-up) under the present conditions (the year 1950) is examined. The results of the control experiment by MIROC4h are compared with simulations of preindustrial conditions carried out for the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4) using the previous high- and medium-resolution versions of the model, called MIROC3h and MIROC3m, respectively. A major change in MIROC4h is a doubling of the resolution of the atmospheric component to 0.5625 degrees, compared to 1.125 degrees for MIROC3h. The oceanic components of MIROC4h and MIROC3h are eddy-permitting, with a horizontal resolution of 0.28125 degrees (zonal) x 0.1875 degrees (meridional). In MIROC3m, the horizontal resolution is 2.8125 degrees for the atmospheric component and 1.40625 degrees (zonal) x 0.56 degrees-1.4 degrees (meridional) for the ocean component.Compared with MIROC3h and MIROC3m, many improvements have been achieved; for example, errors in the surface air temperature and sea surface temperature are smaller, there is less drift of the ocean water temperature in the subsurface-deep ocean, and the frequency of heavy rain is comparable to observations. The fine horizontal resolution in the atmosphere makes orographic wind and its effects on the ocean more realistic than those of the former models, and the treatment of coastal upwelling motion in the ocean has been improved. Phenomena in the atmosphere and ocean related to the El Nino and southern oscillation are now closer to observations than was obtained by MIROC3h and MIROC3m. The effective climate sensitivity for CO2 doubling is calculated to be about 5.7 K, which is much larger than the value obtained using the IPCC AR4 models, and is mainly due to a decrease in the low-level clouds at low latitudes.

DOI： 10.2151/jmsj.2012-301

Temperature scaling pattern dependence on representative concentration pathway emission scenarios 査読

Yasuhiro Ishizaki, Hideo Shiogama, Seita Emori, Tokuta Yokohata, Toru Nozawa, Tomoo Ogura, Manabu Abe, Masakazu Yoshimori, Kiyoshi Takahashi

CLIMATIC CHANGE 112 ( 2 ) 535 - 546 2012年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：SPRINGER

To preserve consistency among developed emission scenarios, the scenarios used in climate modeling, and the climate scenarios available for impact research, the pattern scaling technique is useful technique. The basic assumption of pattern scaling is that the spatial response pattern per 1 K increase in the global mean surface air temperature (SAT) (scaling pattern) is the same among emission scenarios, but this assumption requires further validation. We therefore investigated the dependence of the scaling pattern of the annual mean SAT on GHGs emission scenarios of representative concentration pathways (RCP) and the causes of that dependence using the Model for Interdisciplinary research on Climate 5 developed by Japanese research community. In particular, we focused on the relationships of the dependency with effects of aerosols and Atlantic meridional overturning circulation. We found significant dependencies of the scaling pattern on emission scenarios at middle and high latitudes of the Northern Hemisphere, with differences of > 15 % over parts of East Asia, North America, and Europe. Impact researchers should take into account those dependencies that seriously affect their research. The mid-latitude dependence is caused by differences in sulfate aerosol emissions per 1 K increase in the global mean SAT, and the high-latitude dependence is mainly caused by nonlinear responses of sea ice and ocean heat transport to global warming. Long-term trends in land-use and land-cover changes did not significantly affect the scaling pattern of annual mean SAT, but they might have an effect at different timescales.

DOI： 10.1007/s10584-012-0430-8

Sea-Ice in Twentieth-Century Simulations by New MIROC Coupled Models: A Comparison between Models with High Resolution and with Ice Thickness Distribution 査読

Yoshiki Komuro, Tatsuo Suzuki, Takashi T. Sakamoto, Hiroyasu Hasumi, Masayoshi Ishii, Masahiro Watanabe, Toru Nozawa, Tokuta Yokohata, Teruyuki Nishimura, Koji Ogochi, Seita Emori, Masahide Kimoto

JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN 90A 213 - 232 2012年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：METEOROLOGICAL SOC JAPAN

Sea ice has a large impact on climatic system and its variability. A good reproducibility of the past state of the sea ice in global climate models will reduce uncertainty in future projection. Here, we present sea-ice simulations for new versions of atmosphere-ocean coupled general circulation models, the Model for Interdisciplinary Research on Climate version 4h (MIROC4h) and version 5 (MIROC5), and assess the reproducibility of the sea ice prior to the future projection. The horizontal resolution of MIROC4h is significantly high for a coupled climate model, although its sea-ice component is based on the previous version. MIROC5 employs some improved schemes including subgrid-scale ice thickness distribution.
Hindcast simulations of twentieth-century climate by the new models are compared with observations and with the results of previous versions of MIROC. For the Northern Hemisphere, Arctic sea-ice simulations are improved in both MIROC4h and MIROC5 compared with previous models. MIROC5 generally agrees well with observational data, whereas in MIROC4h, the Arctic sea ice is smaller in summer extent and in thickness. Employment of the ice thickness distribution, which allows large heat exchange through subgrid-scale thin ice regardless of the grid-averaged thickness, and relatively high albedo parameters contribute to reproduce more realistic ice thickness in MIROC5 compared with that in MIROC4h. For the Southern Hemisphere, MIROC4h well reproduces the observed ice edge, especially in winter, while MIROC5 underestimates sea-ice extent. Both models indicate decreasing trends in Arctic sea ice in the late twentieth century. A heat budget analysis of the MIROC5 Arctic Ocean suggests that intensification of ice-albedo feedback accelerates the rate of Arctic ice decline.

DOI： 10.2151/jmsj.2012-A11

Human activity and anomalously warm seasons in Europe 査読

Nikolaos Christidis, Peter A. Stott, Gareth S. Jones, Hideo Shiogama, Toru Nozawa, Juerg Luterbacher

INTERNATIONAL JOURNAL OF CLIMATOLOGY 32 ( 2 ) 225 - 239 2012年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：WILEY

Seasonal mean temperatures averaged over the European region have warmed at a rate of 0.350.52 K/decade since 1980. The last decade has seen record-breaking seasonal temperatures in Europe including the summer of 2003 and the spring, autumn, and winter of 2007. Previous studies have established that European summer warming since the early twentieth century can be attributed to the effects of human influence. The attribution analysis described here employs temperature data from observations and experiments with two climate models and uses optimal fingerprinting to partition the climate response between its anthropogenic and natural components. These responses are subsequently combined with estimates of unforced climate variability to construct distributions of the annual values of seasonal mean temperatures with and without the effect of human activity. We find that in all seasons, anthropogenic forcings have shifted the temperature distributions towards higher values. We compute the associated change in the likelihood of having seasons whose temperatures exceed a pre-specified threshold. We first set the threshold equal to the seasonal temperature observed in a particular year to assess the effect of anthropogenic influences in past seasons. We find that in the last decade (1999-2008) it is extremely likely (probability greater than 95%) that the probability has more than doubled under the influence of human activity in spring and autumn, while for summer it is extremely likely that the probability has at least quadrupled. One of the two models employed in the analysis indicates it is extremely likely the probability has more than doubled in winter too. We also compute the change in probability over a range of temperature thresholds which enables us to provide updates on the likely change in probability attributable to human influence as soon as observations become available. Such near-real time information could be very useful for adaptation planning. (C) Crown Copyright 2010. Published by John Wiley & Sons, Ltd.

DOI： 10.1002/joc.2262

Predictability of a Stepwise Shift in Pacific Climate during the Late 1990s in Hindcast Experiments Using MIROC 査読

Yoshimitsu Chikamoto, Masahide Kimoto, Masayoshi Ishii, Masahiro Watanabe, Toru Nozawa, Takashi Mochizuki, Hiroaki Tatebe, Takashi T. Sakamoto, Yoshiki Komuro, Hideo Shiogama, Masato Mori, Sayaka Yasunaka, Yukiko Imada, Hiroshi Koyama, Masato Nozu, Fei-fei Jin

JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN 90A 1 - 21 2012年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：METEOROLOGICAL SOC JAPAN

Sea surface temperature (SST) predictability in the Pacific on decadal timescales is examined in hindcast experiments using the coupled atmosphere-ocean model MIROC with low, medium, and high resolutions. In these hindcast experiments, initial conditions are obtained from an anomaly assimilation procedure using the observed oceanic temperature and salinity while prescribing natural and anthropogenic forcing based on the IPCC concentration scenarios. Our hindcast experiments show the predictability of SST in the western subtropical Pacific, the Indian Ocean, and the tropics to the North Atlantic. Previous studies have examined the SST predictability in the Indian Ocean and the Atlantic, but SST predictability in the western subtropical Pacific has not been evaluated. In the western Pacific, the observed SST anomalies in the subtropics of both hemispheres increased rapidly from the early 1990s to the early 2000s. While this SST warming in the western subtropical Pacific is partly explained by global warming signals, the predictions of our model initialized in 1995 or 1996 tend to simulate the pattern of the SST increase and the associated precipitation changes. This large climate change around the late 1990s may be related to phenomena such as the recent increase in the typhoon frequency in Taiwan and the weakened East Asian monsoon reported by recent studies.

DOI： 10.2151/jmsj.2012-A01

降水スケ-リグパターンの RCP s排出シナリオ依存性

石崎安洋, 塩竈秀夫, 江守正多, 横畠徳多, 野沢徹, 高橋潔, 小倉知夫, 吉森正和

水文・水資源学会研究発表会要旨集 25 94 - 94 2012年

記述言語：日本語出版者・発行元：水文・水資源学会

降水量は、温暖化の影響評価や適応策を考える上で最も重要な変数の一つである。この降水量の変化は、温暖化の影響に加えて、エアロゾルの排出量の違いによっても引き起こされる。一般に、温暖化の影響評価や適応策を考える際には幅広い範囲の排出シナリオの結果が必要となるが、大気大循環モデルを用いて様々な排出シナリオで予測を行うには膨大な計算機資源が必要となる。パターンスケーリングは、このような幅広い排出シナリオに基づいた将来予測を行うために非常に有益なツールである。パターンスケーリングにおける重要な仮定は、大気大循環モデルの結果から全球上昇気温で規格化された空間パターン（スケーリングパーン)がRCPs間のエアロゾルの排出量の違いが降水量スケーリングパターンに与える影響を調べた。全球平均気温1度あたりの硫酸塩エアロゾルと炭素性エアロゾルの排出量は、北米東部やヨーロッパ、東アジア、南米、アフリカの中央部で優位に異なっていた。一方、全球平均気温1度あたりの降水量の変化は北米東部、東アジア、ギニア湾周辺でRCPs間に優位な違いがみられるが、ヨーロッパや南米の中央部では見られなかった。エアロゾルに大きな変化があった地域では、ヨーロッパを除いて、基本的に全球平均気温1度あたりの降水量変化のRCPs間の違いと全球平均気温1度あたりの蒸発量変化のRCPs間の違いがつりあっている。また、いずれの地域においても、全球平均気温1度あたりのエアロゾルの排出量の減少率がRCP8.5のほうが小さいため、RCP8.5のほうがRCP2.6よりもエアロゾルの影響が大きい。このため、全球平均気温1度あたりの地表面の上向き短波放射の変化はRCP8.5のほうがRCP2.6と比べ大きく、全球平均気温1度あたりの潜熱、顕熱、長波放射の変化もRCP8.5ではRCP2.6と比べて小さい。海上では主に、全球平均気温1度あたりの地表に到達する日射量の変化のRCPs間の違いは、全球平均気温1度あたりの潜熱の変化のRCPs間の違いによって補償されている。一方、陸上では、潜熱だけでなく顕熱と長波放射の変化の違いも重要である。南米中央部で、エアロゾルの減少率にRCPs間で優位な違いがあるにもかかわらず、降水量の変化に違いが表れなかったのは、大部分が陸上であったためである。

DOI： 10.11520/jshwr.25.0.94.0

Verification of the Performance of the Pseudo-Global-Warming Method for Future Climate Changes during June in East Asia 査読

Takao Yoshikane, Fujio Kimura, Hiroaki Kawase, Toru Nozawa

SOLA 8 2012年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：METEOROLOGICAL SOC JAPAN

The performance of the pseudo-global-warming downscaling (PGWDS) method is tested by comparison with the assumed true climate (ATC), which is a downscaling using a general circulation model (GCM) output data directly. The PGWDS is a simple way to downscale for a future climate using current weather data of a GCM added by the long-term mean difference between the present and the future climate projected by a GCM. The verification focuses on the East Asia during the rainy season of June. A significant change in the 30-year averaged monthly precipitation is found around the rain band in the future in both downscaling methods. Between the experiments of the PGWDS and the ATC, no significant differences in temperature and precipitation can be seen except for limited small areas. The findings indicate that the PGWDS has a highly potential to the reliable downscaling of the future climate. In smaller downscaling domains, however, the differences in precipitation increase remarkably near the upstream side of the lateral boundaries. The choice of the downscaling area is a critical issue for accuracy.

DOI： 10.2151/sola.2012-033

An emission pathway for stabilization at 6 Wm(-2) radiative forcing 査読

Toshihiko Masui, Kenichi Matsumoto, Yasuaki Hijioka, Tsuguki Kinoshita, Toru Nozawa, Sawako Ishiwatari, Etsushi Kato, P. R. Shukla, Yoshiki Yamagata, Mikiko Kainuma

CLIMATIC CHANGE 109 ( 1-2 ) 59 - 76 2011年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：SPRINGER

Representative Concentration Pathway 6.0 (RCP6) is a pathway that describes trends in long-term, global emissions of greenhouse gases (GHGs), short-lived species, and land-use/land-cover change leading to a stabilisation of radiative forcing at 6.0 Watts per square meter (Wm(-2)) in the year 2100 without exceeding that value in prior years. Simulated with the Asia-Pacific Integrated Model (AIM), GHG emissions of RCP6 peak around 2060 and then decline through the rest of the century. The energy intensity improvement rates changes from 0.9% per year to 1.5% per year around 2060. Emissions are assumed to be reduced cost-effectively in any period through a global market for emissions permits. The exchange of CO2 between the atmosphere and terrestrial ecosystem through photosynthesis and respiration are estimated with the ecosystem model. The regional emissions, except CO2 and N2O, are downscaled to facilitate transfer to climate models.

DOI： 10.1007/s10584-011-0150-5

Estimation of future surface temperature changes constrained using the future‐present correlated modes in inter‐model variability of CMIP3 multimodel simulations 査読

Manabu Abe, Hideo Shiogama, Toru Nozawa, Seita Emori

Journal of Geophysical Research 116 ( D18 ) D18104 2011年9月

Impact of carbonaceous aerosols on precipitation in tropical Africa during the austral summer in the twentieth century 査読

Hiroaki Kawase, Toshihiko Takemura, Toru Nozawa

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 116 2011年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

We investigate the impacts of anthropogenic aerosols on a precipitation trend observed over tropical Africa during the austral summer in the twentieth century using an atmosphere-ocean general circulation model (medium-resolution version of the Model for Interdisciplinary Research on Climate (MIROC)). We conducted several numerical experiments forced with various combinations of natural and anthropogenic forcings. These experiments indicate that increased carbonaceous aerosols, especially black carbon (BC) aerosols, have played a vital role in the drying trend over tropical Africa, although increased sulfate aerosols contributed to the drying trend at the northern edge of the Intertropical Convergence Zone over tropical Africa. An analysis using an approximated moisture budget equation indicates that the increased carbonaceous aerosols cause the drying trend through an evaporation reduction and a descending anomaly over tropical Africa. The increases in BC and organic carbon aerosols enhance the absorption and scattering of solar radiation, respectively, resulting in reductions of the incident solar radiation, temperature, and evaporation at the surface. On the other hand, the absorption of solar radiation that is due to BC aerosols causes surrounding atmospheric heating in the lower troposphere, leading to an ascending anomaly over the tropical Atlantic Ocean. The ascending anomaly modulates the zonal atmospheric circulation in the Atlantic Ocean, tropical Africa, and the Indian Ocean, which drives a descending anomaly over tropical Africa. Similar atmospheric heating is observed over tropical Africa by atmospheric soundings during the austral summer in the late twentieth century, which supports our results.

DOI： 10.1029/2011JD015933

Estimation of future surface temperature changes constrained using the future-present correlated modes in inter-model variability of CMIP3 multimodel simulations 査読

Manabu Abe, Hideo Shiogama, Toru Nozawa, Seita Emori

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 116 2011年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

This study utilized a new method for future surface temperature changes constrained by model performance in the late 20th century (20C) climate. We applied the singular value decomposition method to investigate covariance between future and present climates in a multimodel ensemble. We established a transfer function between the expansion coefficients of the present and future climate modes. By projecting the observations onto the present modes and using the transfer function, we obtained the best estimates of the future projection. In this study, we extracted the first two significant leading modes. The first mode showed inter-model variation in spatial patterns of temperature change, with Arctic amplification in the future, and the second mode showed variability in temperature change occurring in the southern marginal regions of sea ice in the Arctic for the 20C simulation. Our evaluation suggests that the future warming of the ensemble mean projection underestimated, particularly in the Arctic region. The estimated temperature change depends mainly on the 20C state of the sea ice and surface temperature in the northern North Atlantic Ocean, which are strongly expressed in the first mode of the 20C climate simulation. The leave-one-out cross-validation indicated that our estimation can improve multimodel mean estimates of temperature change in the higher-latitudes of the Northern Hemisphere.

DOI： 10.1029/2010JD015111

Future projections of surface UV‐B in a changing climate 査読

Watanabe Shingo, Sudo K, Nagashima T, Takemura T, Kawase H, Nozawa T

Journal of Geophysical Research: Atmospheres 116 ( D16118 ) 2011年8月

Future changes in tropospheric ozone under Representative Concentration Pathways (RCPs) 査読

Hiroaki Kawase, Tatsuya Nagashima, Kengo Sudo, Toru Nozawa

GEOPHYSICAL RESEARCH LETTERS 38 2011年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

We consider future changes in tropospheric ozone based on the Representative Concentration Pathways (RCPs), which are new emission and concentration scenarios for the 5th coupled model intercomparison project. In contrast to the SRES scenarios, all the RCP scenarios assume an emission reduction of NOx by the late 21st Century that has the potential to achieve tropospheric ozone reduction. However, increasing radiative forcing (RF) due to greenhouse gases and changes in CH4 concentration also contribute to differences in the tropospheric ozone distribution among RCP scenarios. In the RCP4.5 and RCP6.0, assuming the stabilization of RF, the increase in tropospheric ozone due to enhanced residual circulation is cancelled out by the ozone reduction due to ozone precursor reductions. In contrast, in the RCP8.5, assuming increasing RF even after 2100, further enhanced residual circulation and significant increase in CH4 cause a dramatic increase in tropospheric ozone. Citation: Kawase, H., T. Nagashima, K. Sudo, and T. Nozawa (2011), Future changes in tropospheric ozone under Representative Concentration Pathways (RCPs), Geophys. Res. Lett., 38, L05801, doi:10.1029/2010GL046402.

DOI： 10.1029/2010GL046402

Observational constraints indicate risk of drying in the Amazon basin 査読

Hideo Shiogama, Seita Emori, Naota Hanasaki, Manabu Abe, Yuji Masutomi, Kiyoshi Takahashi, Toru Nozawa

NATURE COMMUNICATIONS 2 253 2011年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：NATURE PUBLISHING GROUP

Climate warming due to human activities will be accompanied by hydrological cycle changes. Economies, societies and ecosystems in South America are vulnerable to such water resource changes. Hence, water resource impact assessments for South America, and corresponding adaptation and mitigation policies, have attracted increased attention. However, substantial uncertainties remain in the current water resource assessments that are based on multiple coupled Atmosphere Ocean General Circulation models. This uncertainty varies from significant wetting to catastrophic drying. By applying a statistical method, we characterized the uncertainty and identified global-scale metrics for measuring the reliability of water resource assessments in South America. Here, we show that, although the ensemble mean assessment suggested wetting across most of South America, the observational constraints indicate a higher probability of drying in the Amazon basin. Thus, over-reliance on the consensus of models can lead to inappropriate decision making.

DOI： 10.1038/ncomms1252

Anthropogenic greenhouse gas contribution to flood risk in England and Wales in autumn 2000 査読

Pardeep Pall, Tolu Aina, Daithi A. Stone, Peter A. Stott, Toru Nozawa, Arno G. J. Hilberts, Dag Lohmann, Myles R. Allen

NATURE 470 ( 7334 ) 382 - 385 2011年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：NATURE PUBLISHING GROUP

Interest in attributing the risk of damaging weather-related events to anthropogenic climate change is increasing(1). Yet climate models used to study the attribution problem typically do not resolve the weather systems associated with damaging events(2) such as the UK floods of October and November 2000. Occurring during the wettest autumn in England and Wales since records began in 1766(3,4), these floods damaged nearly 10,000 properties across that region, disrupted services severely, and caused insured losses estimated at 1.3 pound billion (refs 5, 6). Although the flooding was deemed a 'wakeup call' to the impacts of climate change at the time(7), such claims are typically supported only by general thermodynamic arguments that suggest increased extreme precipitation under global warming, but fail(8,9) to account fully for the complex hydrometeorology(4,10) associated with flooding. Here we present a multi-step, physically based 'probabilistic event attribution' framework showing that it is very likely that global anthropogenic greenhouse gas emissions substantially increased the risk of flood occurrence in England and Wales in autumn 2000. Using publicly volunteered distributed computing(11,12), we generate several thousand seasonal-forecast-resolution climate model simulations of autumn 2000 weather, both under realistic conditions, and under conditions as they might have been had these greenhouse gas emissions and the resulting large-scale warming never occurred. Results are fed into a precipitation-runoff model that is used to simulate severe daily river runoff events in England and Wales (proxy indicators of flood events). The precise magnitude of the anthropogenic contribution remains uncertain, but in nine out of ten cases our model results indicate that twentieth-century anthropogenic greenhouse gas emissions increased the risk of floods occurring in England and Wales in autumn 2000 by more than 20%, and in two out of three cases by more than 90%.

DOI： 10.1038/nature09762

Impact of the Assimilation of Sea Ice Concentration Data on an Atmosphere-Ocean-Sea Ice Coupled Simulation of the Arctic Ocean Climate 査読

Takahiro Toyoda, Toshiyuki Awaji, Nozomi Sugiura, Shuhei Masuda, Hiromichi Igarashi, Yuji Sasaki, Yoshihisa Hiyoshi, Yoichi Ishikawa, Takashi Mochizuki, Takashi T. Sakamoto, Hiroaki Tatebe, Yoshiki Komuro, Tatsuo Suzuki, Teruyuki Nishimura, Masato Mori, Yoshimitsu Chikamoto, Sayaka Yasunaka, Yukiko Imada, Miki Arai, Masahiro Watanabe, Hideo Shiogama, Toru Nozawa, Akira Hasegawa, Masayoshi Ishii, Masahide Kimoto

SOLA 7 37 - 40 2011年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：METEOROLOGICAL SOC JAPAN

We have investigated the effects of assimilating sea ice concentration (SIC) data on a simulation of Arctic Ocean climate using an atmosphere-ocean-sea ice coupled model. Our results show that the normal overestimation of summertime SIC in the East Siberian Sea and the Beaufort Sea in simulations without sea-ice data input can be greatly reduced by assimilating sea-ice data and that this improvement is also evident in a following hindcast experiment for 3-4 years after the initialization of the assimilation. In the hindcast experiment, enhanced heat storage in both sea ice and in the ocean surface layer plays a central role in improving the accuracy of the sea ice distribution, particularly in summer. Our detailed investigation suggests that the ice-albedo feedback and the feedback associated with the atmospheric pressure pattern generated by the improved estimation of SIC work more effectively to retain the heat signal after initialization for a coupled atmosphere-ocean-sea ice system prediction. In addition, comparison with field observations confirms that the model fails to produce a realistic feedback loop, which is (presumably) due to inadequacies in both the ice-cloud feedback model and the feedback via the Beaufort Gyre circulation. Further development of coupled models is thus required to better define Arctic Ocean climate processes and to improve the accuracy of their predictions.

DOI： 10.2151/sola.2011-010

MIROC-ESM 2010: Model description and basic results of CMIP5-20c3m experiments 査読

S. Watanabe, T. Hajima, K. Sudo, T. Nagashima, T. Takemura, H. Okajima, T. Nozawa, H. Kawase, M. Abe, T. Yokohata, T. Ise, H. Sato, E. Kato, K. Takata, S. Emori, M. Kawamiya

Geoscientific Model Development 4 ( 4 ) 845 - 872 2011年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Copernicus GmbH

An earth system model (MIROC-ESM 2010) is fully described in terms of each model component and their interactions. Results for the CMIP5 (Coupled Model Intercomparison Project phase 5) historical simulation are presented to demonstrate the model's performance from several perspectives: atmosphere, ocean, sea-ice, land-surface, ocean and terrestrial biogeochemistry, and atmospheric chemistry and aerosols. An atmospheric chemistry coupled version of MIROC-ESM (MIROC-ESM-CHEM 2010) reasonably reproduces transient variations in surface air temperatures for the period 1850-2005, as well as the present-day climatology for the zonal-mean zonal winds and temperatures from the surface to the mesosphere. The historical evolution and global distribution of column ozone and the amount of tropospheric aerosols are reasonably simulated in the model based on the Representative Concentration Pathways' (RCP) historical emissions of these precursors. The simulated distributions of the terrestrial and marine biogeochemistry parameters agree with recent observations, which is encouraging to use the model for future global change projections. © 2011 Author(s).

DOI： 10.5194/gmd-4-845-2011

Impact of carbonaceous aerosols on precipitation in tropical Africa during the austral summer in the 20th Century 査読

Kawase, H, T. Takemura, T. Nozawa

Journal of Geophysical Research 116 ( D18 ) D18116 2011年

Improved Climate Simulation by MIROC5. Mean States, Variability, and Climate Sensitivity 査読

Masahiro Watanabe, Tatsuo Suzuki, Ryouta O'ishi, Yoshiki Komuro, Shingo Watanabe, Seita Emori, Toshihiko Takemura, Minoru Chikira, Tomoo Ogura, Miho Sekiguchi, Kumiko Takata, Dai Yamazaki, Tokuta Yokohata, Toru Nozawa, Hiroyasu Hasumi, Hiroaki Tatebe, Masahide Kimoto

JOURNAL OF CLIMATE 23 ( 23 ) 6312 - 6335 2010年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER METEOROLOGICAL SOC

A new version of the atmosphere ocean general circulation model cooperatively produced by the Japanese research community known as the Model for Interdisciplinary Research on Climate (MIROC) has recently been developed A century long control experiment was performed using the new version (MIROC5) with the standard resolution of the T85 atmosphere and 1 degrees ocean models The climatological mean state and variability are then compared with observations and those in a previous version (MIROC3 2) with two different resolutions (medres hires) coarser and finer than the resolution of MIROC5A few aspects of the mean fields in MIROC5 are similar to or slightly worse than MIROC3 2 but otherwise the climatological features are considerably better In particular improvements are found in precipitation zonal mean atmospheric fields equatorial ocean subsurface fields and the simulation of El Nino-Southern Oscillation The difference between MIROC5 and the previous model is larger than that between the two MIROC3 2 versions indicating a greater effect of updating parameterization schemes on the model climate than increasing the model resolution The mean cloud property obtained from the sophisticated prognostic schemes in MIROC5 shows good agreement with satellite measurements MIROC5 reveals an equilibrium climate sensitivity of 2 6 K which is lower than that in MIROC3 2 by 1 K This is probably due to the negative feedback of low clouds to the increasing concentration of CO2 which is opposite to that in MIROC3 2

DOI： 10.1175/2010JCLI3679.1

Physical mechanism of long-term drying trend over tropical North Africa (vol 37, L21706, 2010) 査読

Hiroaki Kawase, Manabu Abe, Yukiko Yamada, Toshihiko Takemura, Tokuta Yokohata, Toru Nozawa

GEOPHYSICAL RESEARCH LETTERS 37 2010年11月

Probabilistic estimates of recent changes in temperature: a multi-scale attribution analysis 査読

Nikolaos Christidis, Peter A. Stott, Francis W. Zwiers, Hideo Shiogama, Toru Nozawa

CLIMATE DYNAMICS 34 ( 7-8 ) 1139 - 1156 2010年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：SPRINGER

The role of anthropogenic forcings in temperature changes during recent decades is investigated over a range of spatial scales. Changes in the annual mean surface temperature and also in the warmest night of the year, which has implications for human health, are considered. Distributions of regional trends with and without the effect of human activity are produced, using constraints from a global optimal detection analysis. Anthropogenic forcings are estimated to have more than doubled the likelihood of mean warming in all regions considered except central North America, where results are more model dependent. The likelihood of warming of the warmest night has also increased, but the estimated change is more uncertain. Inferences on sub-continental scales are indicative rather than definitive because of the absence of locally important forcings and processes in model simulations, as well as model biases. As model inconsistencies may impact regional analyses, a multi-model approach is essential.

DOI： 10.1007/s00382-009-0615-7

Emission Scenario Dependency of Precipitation on Global Warming in the MIROC3.2 Model 査読

Hideo Shiogama, Seita Emori, Kiyoshi Takahashi, Tatsuya Nagashima, Tomoo Ogura, Toru Nozawa, Toshihiko Takemura

JOURNAL OF CLIMATE 23 ( 9 ) 2404 - 2417 2010年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER METEOROLOGICAL SOC

The precipitation sensitivity per 1 K of global warming in twenty-first-century climate projections is smaller in an emission scenario with larger greenhouse gas concentrations and aerosol emissions, according to the Model for Interdisciplinary Research on Climate 3.2 (MIROC3.2) coupled atmosphere-ocean general circulation model. The authors examined the reasons for the precipitation sensitivity to emission scenarios by performing separated individual forcing runs under high and low emission scenarios. It was found that the dependency on emission scenario is mainly caused by differences in black and organic carbon aerosol forcing (the sum of which is cooling forcing) between the emission scenarios and that the precipitation is more sensitive to carbon aerosols than well-mixed greenhouse gases. They also investigated the reason for the larger precipitation sensitivity (larger magnitude of precipitation decrease per 1 K cooling of temperature) in the carbon aerosol runs. Surface dimming due to the direct and indirect effects of carbon aerosols effectively decreases evaporation and precipitation, which enhances the precipitation sensitivity in the carbon aerosol runs. In terms of the atmospheric moisture cycle, although changes of vertical circulation offset the effects of changes in the atmospheric moisture in both the carbon aerosol and greenhouse gas runs, the amplitude of vertical circulation change per 1 K temperature change is less in the carbon aerosol runs. Furthermore, the second indirect effect of organic carbon aerosol counteracts the influence of the vertical circulation change. These factors lead to suppression of changes in the moisture's atmospheric residence time and increase of the precipitation sensitivity in the carbon aerosol runs.

DOI： 10.1175/2009JCLI3428.1

Physical mechanism of long-term drying trend over tropical North Africa 査読

Hiroaki Kawase, Manabu Abe, Yukiko Yamada, Toshihiko Takemura, Tokuta Yokohata, Toru Nozawa

GEOPHYSICAL RESEARCH LETTERS 37 2010年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

Based on an approximated moisture budget equation, we investigate the physical mechanisms of a drying trend observed over tropical North Africa in the boreal summer during the 20th Century by analyzing datasets of several climate-model experiments forced with various combinations of natural and anthropogenic forcings. Increased anthropogenic aerosols thermodynamically induce a drying trend due to a tropospheric cooling and dynamically induce an additional drying trend due to an atmospheric local circulation change stirred up by the strong gradient of a sea surface temperature anomaly over the tropical Atlantic Ocean. Increased greenhouse gases, on the other hand, induce a drying trend through the large-scale dynamic effect, which is canceled out by the thermodynamically induced moistening trend due to tropospheric warming. Therefore, the drying trend observed over tropical North Africa during the 20th Century is strongly affected by the increased anthropogenic aerosols through both the dynamic and thermodynamic effects. Citation: Kawase, H., M. Abe, Y. Yamada, T. Takemura, T. Yokohata, and T. Nozawa (2010), Physical mechanism of long term drying trend over tropical North Africa, Geophys. Res. Lett., 37, L09706, doi: 10.1029/2010GL043038.

DOI： 10.1029/2010GL043038

Emission scenario dependencies in climate change assessments of the hydrological cycle 査読

Hideo Shiogama, Naota Hanasaki, Yuji Masutomi, Tatsuya Nagashima, Tomoo Ogura, Kiyoshi Takahashi, Yasuaki Hijioka, Toshihiko Takemura, Toru Nozawa, Seita Emori

CLIMATIC CHANGE 99 ( 1-2 ) 321 - 329 2010年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：SPRINGER

Anthropogenic global warming will lead to changes in the global hydrological cycle. The uncertainty in precipitation sensitivity per 1 K of global warming across coupled atmosphere-ocean general circulation models (AOGCMs) has been actively examined. On the other hand, the uncertainty in precipitation sensitivity in different emission scenarios of greenhouse gases (GHGs) and aerosols has received little attention. Here we show a robust emission-scenario dependency (ESD); smaller global precipitation sensitivities occur in higher GHG and aerosol emission scenarios. Although previous studies have applied this ESD to the multi-AOGCM mean, our surprising finding is that current AOGCMs all have the common ESD in the same direction. Different aerosol emissions lead to this ESD. The implications of the ESD of precipitation sensitivity extend far beyond climate analyses. As we show, the ESD potentially propagates into considerable biases in impact assessments of the hydrological cycle via a widely used technique, so-called pattern scaling. Since pattern scaling is essential to conducting parallel analyses across climate, impact, adaptation and mitigation scenarios in the next report from the Intergovernmental Panel on Climate Change, more attention should be paid to the ESD of precipitation sensitivity.

DOI： 10.1007/s10584-009-9765-1

Pacific decadal oscillation hindcasts relevant to near-term climate prediction 査読

Takashi Mochizuki, Masayoshi Ishii, Masahide Kimoto, Yoshimitsu Chikamoto, Masahiro Watanabe, Toru Nozawa, Takashi T. Sakamoto, Hideo Shiogama, Toshiyuki Awaji, Nozomi Sugiura, Takahiro Toyoda, Sayaka Yasunaka, Hiroaki Tatebe, Masato Mori

PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 107 ( 5 ) 1833 - 1837 2010年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：NATL ACAD SCIENCES

Decadal-scale climate variations over the Pacific Ocean and its surroundings are strongly related to the so-called Pacific decadal oscillation (PDO) which is coherent with wintertime climate over North America and Asian monsoon, and have important impacts on marine ecosystems and fisheries. In a near-term climate prediction covering the period up to 2030, we require knowledge of the future state of internal variations in the climate system such as the PDO as well as the global warming signal. We perform sets of ensemble hindcast and forecast experiments using a coupled atmosphere-ocean climate model to examine the predictability of internal variations on decadal timescales, in addition to the response to external forcing due to changes in concentrations of greenhouse gases and aerosols, volcanic activity, and solar cycle variations. Our results highlight that an initialization of the upper-ocean state using historical observations is effective for successful hindcasts of the PDO and has a great impact on future predictions. Ensemble hindcasts for the 20th century demonstrate a predictive skill in the upper-ocean temperature over almost a decade, particularly around the Kuroshio-Oyashio extension (KOE) and subtropical oceanic frontal regions where the PDO signals are observed strongest. A negative tendency of the predicted PDO phase in the coming decade will enhance the rising trend in surface air-temperature (SAT) over east Asia and over the KOE region, and suppress it along the west coasts of North and South America and over the equatorial Pacific. This suppression will contribute to a slowing down of the global-mean SAT rise.

DOI： 10.1073/pnas.0906531107

Possible Influence of Volcanic Activity on the Decadal Potential Predictability of the Natural Variability in Near-Term Climate Predictions 査読

Hideo Shiogama, Seita Emori, Takashi Mochizuki, Sayaka Yasunaka, Tokuta Yokohata, Masayoshi Ishii, Toru Nozawa, Masahide Kimoto

ADVANCES IN METEOROLOGY 2010 2010年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：HINDAWI LTD

Initialization based on data assimilations using historical observations possibly improves near-term climate predictions. Significant volcanic activity in the future is unpredictable and not assumed in future climate predictions. To examine the possible influence of unpredictable future volcanic activity on the decadal potential predictability of the natural variability, we performed a 2006-2035 climate prediction experiment with the assumption that the 1991 Mt. Pinatubo eruption would take place again in 2010. The Pinatubo forcing induced not only significant cooling responses but also considerable noises in the natural variability. The errors due to the Pinatubo forcing grew faster than that arising from imperfect knowledge of the observed state, leading to a rapid reduction of the decadal potential predictability of the natural variability.

DOI： 10.1155/2010/657318

Correlation between Inter-Model Similarities in Spatial Pattern for Present and Projected Future Mean Climate 査読

Manabu Abe, Hideo Shiogama, Julia C. Hargreaves, James D. Annan, Toru Nozawa, Seita Emori

SOLA 5 133 - 136 2009年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：METEOROLOGICAL SOC JAPAN

When an averaging method is used for model future projection with weights determined according to the model performance in the present climate, generally, the stationarity of the model performance between present and future is implicitly assumed. Here we investigate this assumption using multi-model data. We consider the correlation between inter-model similarities in the spatial pattern for the present-day climate and future climate change for surface air temperature, precipitation and sea level pressure on global and zonal domains in the seasonal time scale. We further extend previous work by devising a bootstrap method to estimate the statistical significance of all correlations, which have previously not been estimated. Most of the correlation coefficients for precipitation were significant, but moderate or low in the absolute value. Many of those for the other variables were not significant. Also, we discuss the magnitude of the inter-model similarity used in this work.

DOI： 10.2151/sola.2009-034

Visualization of huge climate data with high-speed spherical self-organizing map

Kanta Tachibana, Norihiko Sugimoto, Hideo Shiogama, Toru Nozawa

Journal of Advanced Computational Intelligence and Intelligent Informatics 13 ( 3 ) 210 - 216 2009年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：Fuji Technology Press

We propose the use of a high-speed spherical selforganizing map (HSS-SOM) to visualize climate variability as a complementary alternative to empirical orthogonal function (EOF) analysis. EOF analysis, which is the same as principal component analysis, is often used in the fields of meteorology and climatology to extract leading climate variability patterns, its production of linear mapping with only a low contribution rate may preclude producing any meaningful results. Due to computational limitations, however, conventional self-organizing maps are difficult to apply to huge climate datasets. The development of HSSSOMs with dynamically growing neurons has helped reduce computational time. After demonstrating validity of our HSS-SOM using observational climate data and HSS-SOM effectiveness as a complementary alternative to the EOF, we extract dominant atmospheric circulation patterns from huge amounts of climate data in the general circulation model, in which both present climatology and future climate are simulated. These patterns correspond to those obtained in previous studies, indicating the HSS-SOM's usefulness in climate research.

DOI： 10.20965/jaciii.2009.p0210

Attribution of Declining Western US Snowpack to Human Effects 査読

David W. Pierce, Tim P. Barnett, Hugo G. Hidalgo, Tapash Das, Celine Bonfils, Benjamin D. Santer, Govindasamy Bala, Michael D. Dettinger, Daniel R. Cayan, Art Mirin, Andrew W. Wood, Toru Nozawa

JOURNAL OF CLIMATE 21 ( 23 ) 6425 - 6444 2008年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER METEOROLOGICAL SOC

Observations show snowpack has declined across much of the western United States over the period 1950-99. This reduction has important social and economic implications, as water retained in the snowpack from winter storms forms an important part of the hydrological cycle and water supply in the region. A formal model-based detection and attribution (D-A) study of these reductions is performed. The detection variable is the ratio of 1 April snow water equivalent (SWE) to water-year-to-date precipitation (P), chosen to reduce the effect of P variability on the results. Estimates of natural internal climate variability are obtained from 1600 years of two control simulations performed with fully coupled ocean-atmosphere climate models. Estimates of the SWE/P response to anthropogenic greenhouse gases, ozone, and some aerosols are taken from multiple-member ensembles of perturbation experiments run with two models. The D-A shows the observations and anthropogenically forced models have greater SWE/P reductions than can be explained by natural internal climate variability alone. Model-estimated effects of changes in solar and volcanic forcing likewise do not explain the SWE/P reductions. The mean model estimate is that about half of the SWE/P reductions observed in the west from 1950 to 1999 are the result of climate changes forced by anthropogenic greenhouse gases, ozone, and aerosols.

DOI： 10.1175/2008JCLI2405.1

Detection and Attribution of Temperature Changes in the Mountainous Western United States 査読

Celine Bonfils, Benjamin D. Santer, David W. Pierce, Hugo G. Hidalgo, Govindasamy Bala, Tapash Das, Tim P. Barnett, Daniel R. Cayan, Charles Doutriaux, Andrew W. Wood, Art Mirin, Toru Nozawa

JOURNAL OF CLIMATE 21 ( 23 ) 6404 - 6424 2008年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER METEOROLOGICAL SOC

Large changes in the hydrology of the western United States have been observed since the mid-twentieth century. These include a reduction in the amount of precipitation arriving as snow, a decline in snowpack at low and midelevations, and a shift toward earlier arrival of both snowmelt and the centroid (center of mass) of streamflows. To project future water supply reliability, it is crucial to obtain a better understanding of the underlying cause or causes for these changes. A regional warming is often posited as the cause of these changes without formal testing of different competitive explanations for the warming. In this study, a rigorous detection and attribution analysis is performed to determine the causes of the late winter/early spring changes in hydrologically relevant temperature variables over mountain ranges of the western United States. Natural internal climate variability, as estimated from two long control climate model simulations, is insufficient to explain the rapid increase in daily minimum and maximum temperatures, the sharp decline in frost days, and the rise in degree-days above 0 degrees C (a simple proxy for temperature-driven snowmelt). These observed changes are also inconsistent with the model-predicted responses to variability in solar irradiance and volcanic activity. The observations are consistent with climate simulations that include the combined effects of anthropogenic greenhouse gases and aerosols. It is found that, for each temperature variable considered, an anthropogenic signal is identifiable in observational fields. The results are robust to uncertainties in model-estimated fingerprints and natural variability noise, to the choice of statistical down-scaling method, and to various processing options in the detection and attribution method.

DOI： 10.1175/2008JCLI2397.1

Impacts of Global Warming on Hydrological Cycles in the Asian Monsoon Region 査読

Koji Dairaku, Seita Emori, Toru Nozawa

ADVANCES IN ATMOSPHERIC SCIENCES 25 ( 6 ) 960 - 973 2008年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：SCIENCE PRESS

The hydrologic changes and the impact of these changes constitute a fundamental global-warning-related concern. Faced with threats to human life and natural ecosystems, such as droughts, floods, and soil erosion, water resource planners must increasingly make future risk assessments. Though hydrological predictions associated with the global climate change are already being performed, mainly through the rise of GCMs, coarse spatial resolution and uncertain physical processes limit the representation of terrestrial water/energy interactions and the, variability in such systems its the Asian monsoon. Despite numerous studies, the regional responses of hydrologic changes resulting front climate change remains inconclusive. In this paper, an attempt at dynamical downscaling of future hydrologic projection under global climate change in Asia is addressed. The authors conducted present and future Asian regional climate simulations which were nested in the result's of Atmospheric General Circulation Model (AGCM) experiments. The regional climate model could capture the general simulated features of the AGCM. Also, some regional phenomena such as orographic precipitation, which did not appear in the outcome of the AGCM simulation, were successfully produced. Under global warning. the increase of water vapor associated with the warmed air temperature was projected. It was projected to bring more abundant water vapor to the southern portions of India and the Bay of Bengal, and to enhance precipitation especially over the mountainous regions, the western part of India and the southern edge of the Tibetan Plateau. As a result of the changes in the synoptic flow patterns and precipitation under global warming, the increases of annual mean precipitation and surface runoff were projected in many regions of Asia. However, both the positive and negative changes of seasonal surface runoff were projected in some regions which will increase the flood risk and cause a mismatch between water demand and water availability in the agricultural season.

DOI： 10.1007/s00376-008-0960-1

Attribution of polar warming to human influence 査読

Nathan P. Gillett, Daithi A. Stone, Peter A. Stott, Toru Nozawa, Alexey Yu. Karpechko, Gabriele C. Hegerl, Michael F. Wehner, Philip D. Jones

NATURE GEOSCIENCE 1 ( 11 ) 750 - 754 2008年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：NATURE PUBLISHING GROUP

The polar regions have long been expected to warm strongly as a result of anthropogenic climate change, because of the positive feedbacks associated with melting ice and snow(1,2). Several studies have noted a rise in Arctic temperatures over recent decades(2-4), but have not formally attributed the changes to human influence, owing to sparse observations and large natural variability(5,6). Both warming and cooling trends have been observed in Antarctica(7), which the Intergovernmental Panel on Climate Change Fourth Assessment Report concludes is the only continent where anthropogenic temperature changes have not been detected so far, possibly as a result of insufficient observational coverage(8). Here we use an up-to-date gridded data set of land surface temperatures(9,10) and simulations from four coupled climate models to assess the causes of the observed polar temperature changes. We find that the observed changes in Arctic and Antarctic temperatures are not consistent with internal climate variability or natural climate drivers alone, and are directly attributable to human influence. Our results demonstrate that human activities have already caused significant warming in both polar regions, with likely impacts on polar biology, indigenous communities(2), ice-sheet mass balance and global sea level(11).

DOI： 10.1038/ngeo338

Comparison of equilibrium and transient responses to CO2 increase in eight state-of-the-art climate models 査読

Tokuta Yokohata, Seita Emori, Toru Nozawa, Tomoo Ogura, Michio Kawamiya, Yoko Tsushima, Tatsuo Suzuki, Seiji Yukimoto, Ayako Abe-Ouchi, Hiroyasu Hasumi, Akimasa Sumi, Masahide Kimoto

TELLUS SERIES A-DYNAMIC METEOROLOGY AND OCEANOGRAPHY 60 ( 5 ) 946 - 961 2008年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：TAYLOR & FRANCIS LTD

We compared the climate response of doubled CO2 equilibrium experiments ( 2 x CO2) by atmosphere-slab ocean coupled general circulation models ( ASGCMs) and that of 1% per year CO2 increase experiments ( 1% CO2 by atmosphere-ocean coupled general circulation models (AOGCMs) using eight state-of-the-art climate models. Climate feedback processes in 2 x CO2 are different from those in 1% CO2, and the equilibrium climate sensitivity (T-2x) in 2 x CO2 is different from the effective climate sensitivity (T-2x,(eff)) in 1% CO2. The difference between T-2x and T-2x,T-eff is from - 1.3 to 1.6 K, a large part of which can be explained by the difference in the ice-albedo and cloud feedback. The largest contribution is cloud SW feedback, and the difference in cloud SW feedback for 2 x CO2 and 1% CO2 could be determined by the distribution of the SAT anomaly which causes differences in the atmospheric thermal structure. An important factor which determines the difference in ice-albedo feedback is the initial sea ice distribution at the Southern Ocean, which is generally overestimated in 2 x CO2 as compared to 1%CO2 and observation. Through the comparison of climate feedback processes in 2 x CO2 and 1%CO2, the possible behaviour of the time evolution of T-2x,T-eff is discussed.

DOI： 10.1111/j.1600-0870.2008.00345.x

Human-induced changes in the hydrology of the western United States 査読

Tim P. Barnett, David W. Pierce, Hugo G. Hidalgo, Celine Bonfils, Benjamin D. Santer, Tapash Das, Govindasamy Bala, Andrew W. Wood, Toru Nozawa, Arthur A. Mirin, Daniel R. Cayan, Michael D. Dettinger

SCIENCE 319 ( 5866 ) 1080 - 1083 2008年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER ASSOC ADVANCEMENT SCIENCE

Observations have shown that the hydrological cycle of the western United States changed significantly over the last half of the 20th century. We present a regional, multivariable climate change detection and attribution study, using a high- resolution hydrologic model forced by global climate models, focusing on the changes that have already affected this primarily arid region with a large and growing population. The results show that up to 60% of the climate- related trends of river flow, winter air temperature, and snow pack between 1950 and 1999 are human- induced. These results are robust to perturbation of study variates and methods. They portend, in conjunction with previous work, a coming crisis in water supply for the western United States.

DOI： 10.1126/science.1152538

Changes in Mean and Extreme Precipitation in Near-term Predictions up to the Year 2030 査読

Hideo Shiogama, Akira Hasegawa, Toru Nozawa, Seita Emori

SOLA 4 17 - 20 2008年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：METEOROLOGICAL SOC JAPAN

We show the near-term predictions of mean and extreme precipitation up to the year 2030 by analyzing ten-member ensemble runs with perturbed initial conditions of the MIROC model. Mean and extreme precipitation increase in high latitudes and the tropics, and decrease in the subtropics in the ensemble mean. Uncertainty due to natural variability was also examined. Most of the ten runs predict positive anomalies in high latitudes and some parts of the tropics. Changes in parts of the subtropics are uncertain due to natural variability. Thermodynamic changes mainly explain robust total increases in mean precipitation in high latitudes and the tropics. Thermodynamic changes of mean precipitation are uncertain in the subtropics, resulting in a large uncertainty in total changes. It is suggested that small signal-to-noise rations of thermodynamic changes in the subtropics are induced by regional decreases in relative humidity at lower troposphere, which counteract the effects of increased column-integrated water vapor.

DOI： 10.2151/sola.2008-005

Detection of human influence on twentieth-century precipitation trends 査読

Xuebin Zhang, Francis W. Zwiers, Gabriele C. Hegerl, F. Hugo Lambert, Nathan P. Gillett, Susan Solomon, Peter A. Stott, Toru Nozawa

NATURE 448 ( 7152 ) 461 - U4 2007年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：NATURE PUBLISHING GROUP

Human influence on climate has been detected in surface air temperature(1-5), sea level pressure(6), free atmospheric temperature(7), tropopause height(8) and ocean heat content(9). Human-induced changes have not, however, previously been detected in precipitation at the global scale(10-12), partly because changes in precipitation in different regions cancel each other out and thereby reduce the strength of the global average signal(13-19). Models suggest that anthropogenic forcing should have caused a small increase in global mean precipitation and a latitudinal redistribution of precipitation, increasing precipitation at high latitudes, decreasing precipitation at sub-tropical latitudes(15,18,19), and possibly changing the distribution of precipitation within the tropics by shifting the position of the Intertropical Convergence Zone(20). Here we compare observed changes in land precipitation during the twentieth century averaged over latitudinal bands with changes simulated by fourteen climate models. We show that anthropogenic forcing has had a detectable influence on observed changes in average precipitation within latitudinal bands, and that these changes cannot be explained by internal climate variability or natural forcing. We estimate that anthropogenic forcing contributed significantly to observed increases in precipitation in the Northern Hemisphere mid-latitudes, drying in the Northern Hemisphere subtropics and tropics, and moistening in the Southern Hemisphere subtropics and deep tropics. The observed changes, which are larger than estimated from model simulations, may have already had significant effects on ecosystems, agriculture and human health in regions that are sensitive to changes in precipitation, such as the Sahel.

DOI： 10.1038/nature06025

Robustness of climate change signals in near term predictions up to the year 2030: Changes in the frequency of temperature extremes 査読

Hideo Shiogama, Toru Nozawa, Seita Emori

GEOPHYSICAL RESEARCH LETTERS 34 ( 12 ) L12714 2007年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

This is the first study to examine whether human contributions to changes in extreme temperature indices have larger amplitudes than natural variability in near future ( up to 2030) climate prediction. We performed 10 runs of the initial condition perturbed ensemble of a coupled atmosphere-ocean general circulation model. In the near future, over most land areas, all 10 runs predict more frequent occurrences of warm nights and warm days, and less frequent cold nights and cold days, suggesting that human influences have become larger than natural variability. The fraction of areas where all runs agree on the direction of changes over land is less sensitive to ensemble sizes ( for warm nights, 96% and 93% for 4 runs and 10 runs, respectively). The changes in the frequency of warm and cold extremes are mainly due to shifts in seasonal mean temperatures. Additionally snow cover affects the frequency of cold extremes in some areas.

DOI： 10.1029/2007GL029318

Different transient climate responses of two versions of an atmosphere-ocean coupled general circulation model 査読

T. Yokohata, S. Emori, T. Nozawa, T. Ogura, N. Okada, T. Suzuki, Y. Tsushima, M. Kawamiya, A. Abe-Ouchi, H. Hasumi, A. Sumi, M. Kimoto

GEOPHYSICAL RESEARCH LETTERS 34 ( 2 ) 2007年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

[1] The Model for Interdisciplinary Research on Climate (MIROC), an atmosphere-ocean coupled general circulation model (AOGCM), has two versions with different resolutions, high (Hi-Res) and medium (Mid-Res). While their equilibrium climate sensitivities (ECS) to CO2 increases are similar, the transient climate response (TCR) of the Hi-Res version is larger than that of the Mid-Res version. The former shows the highest transient response among the Intergovernmental Panel on Climate Change (IPCC) fourth assessment report (AR4) climate models. Our climate feedback analysis indicates that the higher TCR of the Hi-Res version mainly comes from its larger ice-albedo feedback (SFC-SW) and lower ocean heat uptake (OHU). Since the Hi-Res version shows better agreement with observation than the Mid-Res version concerning the factors that affect the SFC-SW and OHU, the TCR of the Hi-Res version is not considered to be unrealistic compared to that of the Mid-Res version. On the other hand, the two versions have similar SFC-SW values and negligible OHU in ECS experiments performed by the atmosphere-slab ocean coupled general circulation model (ASGCM). In the ASGCM, the difference in SFC-SW between the two versions was likely suppressed due to artificial fluxes applied to the ocean and sea-ice system.

DOI： 10.1029/2006GL027966

その他リンク： http://orcid.org/0000-0003-1745-5952

Time evolutions of various radiative forcings for the past 150 years estimated by a general circulation model 査読

Toshihiko Takemura, Yoko Tsushima, Tokuta Yokohata, Toru Nozawa, Tatsuya Nagashima, Teruyuki Nakajima

GEOPHYSICAL RESEARCH LETTERS 33 ( 19 ) 2006年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

Time series of the instantaneous radiative forcings for main anthropogenic and natural forcing agents from the year 1850 to 2000 are evaluated at the Earth's surface as well as at the tropopause with an atmospheric general circulation model. This evaluation corresponds to a simulation of 20th century climate with a synthetic coupled atmosphere-ocean general circulation model. The evaluation indicates that the positive radiative forcing at the tropopause rapidly increases from 1910 to 1950 and after 1970 principally due to long-lived greenhouse gases, while the negative radiative forcing at the surface sharply increases between 1955 and 1965 mainly due to the aerosol direct and indirect effects. This study suggests that a simultaneous analysis of changing rates of the radiative forcing both at the tropopause and surface can explain tendencies of changes in the surface air temperature.

DOI： 10.1029/2006GL026666

Influence of volcanic activity and changes in solar irradiance on surface air temperatures in the early twentieth century 査読

H Shiogama, T Nagashima, T Yokohata, SA Crooks, T Nozawa

GEOPHYSICAL RESEARCH LETTERS 33 ( 9 ) L09702 - L09702 2006年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

Causes of the global surface air temperature warming in the early half of the 20th century are examined using a climate model and an optimal detection/attribution methodology. While the anthropogenic response seems to be underestimated in our model, our previous study detected the influence due to natural external forcing, including the combined effects of solar irradiance changes and the recovery from large volcanic activity. We further partition the responses between these two natural external factors, detecting both the solar and the volcanic signal in the observed early warming. A diagnosis of the sensitivity to solar forcing and a volcanic super-eruption simulation suggest that our model possesses larger climate sensitivities to solar forcing and longer relaxation times to volcanic forcing than HadCM3, enabling us to detect both the solar and volcanic forcing responses.

DOI： 10.1029/2005GL025622

Effect of carbonaceous aerosols on surface temperature in the mid twentieth century 査読

T Nagashima, H Shiogama, T Yokohata, T Takemura, SA Crooks, T Nozawa

GEOPHYSICAL RESEARCH LETTERS 33 ( 4 ) L04702 - L04702 2006年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

Simulations using a climate model are used to investigate the possible impact of increasing emissions of carbonaceous aerosols on near-surface temperature in the mid-20th century. The annual global mean near-surface temperature change from the mid-20th century onward is reasonably described by a model that is forced by changes in most of the known climate forcing agents including an increase in carbonaceous aerosols, though it can also be well reproduced without increases in carbonaceous aerosols. However, if we consider spatio-temporal structure of the changes in the near-surface temperature, an increase in carbonaceous aerosols is definitely required for the model to represent changes in the near-surface temperature in the mid-century, in particular, cooling trends in the tropical and subtropical continents. The significance of an increase in carbonaceous aerosols as an indispensable contributor to mid-20th century temperature changes is confirmed with the use of an optimal fingerprinting methodology.

DOI： 10.1029/2005GL024887

Detection of Greenhouse Gas and Aerosol Influences on Changes in Temperature Extremes 査読

Hideo Shiogama, Nikolaos Christidis, John Caesar, Tokuta Yokohata, Toru Nozawa, Seita Emori

SOLA 2 152 - 155 2006年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：METEOROLOGICAL SOC JAPAN

Detection/attribution analyses of temperature extremes were carried out by comparing a new gridded observational dataset of daily maximum/minimum temperatures (HadGHCND) and the simulation of MIROC3.2. It was shown that significant anthropogenic warming is detectable in the annual warmest night, and the coldest day and night from 1950 to 1999, while human influence was not detected in the warmest day. These findings are in agreement with a previous study that examined the simulation of HadCM3. Human influence is also identified in the decrease in the number of frost days, but not with the increase in the number of summer days. Furthermore, it was suggested that half of the warming trend due to rising greenhouse gas concentrations is canceled out by other factors, predominantly aerosol cooling. It is expected that a rapid decline of aerosol emissions coupled with rising greenhouse gas concentrations would induce larger changes in temperature extremes in the future.

DOI： 10.2151/sola.2006-039

Climate response to volcanic forcing: Validation of climate sensitivity of a coupled atmosphere-ocean general circulation model 査読

T Yokohata, S Emori, T Nozawa, Y Tsushima, T Ogura, M Kimoto

GEOPHYSICAL RESEARCH LETTERS 32 ( 21 ) 1 - 4 2005年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

Two versions of a coupled atmosphere-ocean general circulation model (GCM) with different climate sensitivities are tested on global cooling following the Pinatubo volcanic eruption to investigate the validity of high climate sensitivities. The higher-sensitivity version, with climate sensitivity of 6.3 K for doubled CO2 forcing, overestimates cooling due to the volcanic eruption, whereas the lower-sensitivity version (4.0 K) produces results consistent with observations. A simple scheme for climate feedback analysis is devised and it is found that the difference between the two versions is attributed to cloud-albedo feedback. This validation method is expected to provide additional constraints on climate sensitivity and possibly lead to reduced uncertainties in climate prediction.

DOI： 10.1029/2005GL023542

Anthropogenic and natural forcing impacts on ENSO-like decadal variability during the second half of the 20th century 査読

H Shiogama, M Watanabe, M Kimoto, T Nozawa

GEOPHYSICAL RESEARCH LETTERS 32 ( 21 ) L21714-L21714-4 - L21714 2005年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

Several climate simulations, performed with an atmosphere-ocean coupled general circulation model, are made to evaluate the influences of anthropogenic and natural external forcing on the observed fluctuation of the Decadal El Nino-Southern Oscillation (DENSO) during the second half of the 20th century. A comparison of DENSO in the model simulations and the observations suggests that the observed variability includes an unusually large trend relative to that expected from purely natural variations. Moreover, we show that there is a large probability that this trend is mainly attributable to anthropogenic factors.

DOI： 10.1029/2005GL023871

A simple scheme for climate feedback analysis 査読

T Yokohata, S Emori, T Nozawa, Y Tsushima, T Ogura, M Kimoto

GEOPHYSICAL RESEARCH LETTERS 32 ( 19 ) 1 - 4 2005年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

In this study we present a simple scheme for the diagnosis of the strength of climate feedback. The scheme is based on straightforward calculations using the conventional output of a general circulation model ( GCM), and evaluates the major radiative feedbacks concerning the surface, clear- sky atmosphere, and clouds. We place an emphasis on evaluating shortwave ( SW) feedbacks. Assumptions involved in extracting the SW surface feedback are validated by accurate calculations and considered to be acceptable. The performance of our scheme is demonstrated via a doubled CO2 experiment. Compared to conventional methods, we can evaluate SW feedbacks more accurately while the evaluation of LW feedbacks is essentially similar between the two methods. The ready application of our scheme to the output of various GCMs should be of great use for multi- model ensemble analyses, which contribute to reducing the uncertainty in future climate projections.

DOI： 10.1029/2005GL023673

Detecting natural influence on surface air temperature change in the early twentieth century 査読

T Nozawa, T Nagashima, H Shiogama, SA Crooks

GEOPHYSICAL RESEARCH LETTERS 32 ( 20 ) L20719 - L20719 2005年10月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

We analyze surface air temperature datasets simulated by a coupled climate model forced with different external forcings, to diagnose the relative importance of these forcings to the observed warming in the early 20th century. The geographical distribution of linear temperature trends in the simulations forced only by natural contributions (volcanic eruptions and solar variability) shows better agreement with observed trends than that does the simulations forced only by well-mixed greenhouse gases. Using an optimal fingerprinting technique we robustly detect a significant natural contribution to the early 20th century warming. In addition, the amplitude of our simulated natural signal is consistent with the observations. Over the same period, however, we could not detect a greenhouse gas signal in the observed surface temperature in the presence of the external natural forcings. Hence our analysis suggests that external natural factors caused more warming in the early 20th century than anthropogenic factors.

DOI： 10.1029/2005GL023540

Simulation of climate response to aerosol direct and indirect effects with aerosol transport-radiation model 査読

Toshihiko Takemura, Toru Nozawa, Seita Emori, Takashi Y. Nakajima, Teruyuki Nakajima

Journal of Geophysical Research D: Atmospheres 110 ( 2 ) 1 - 16 2005年1月

記述言語：英語掲載種別：研究論文（学術雑誌）

With a global aerosol transport-radiation model coupled to a general circulation model, changes in the meteorological parameters of clouds, precipitation, and temperature caused by the direct and indirect effects of aerosols are simulated, and its radiative forcing are calculated. A microphysical parameterization diagnosing the cloud droplet number concentration based on the Köhler theory is introduced into the model, which depends not only on the aerosol particle number concentration but also on the updraft velocity, size distributions, and chemical properties of each aerosol species and saturation condition of the water vapor. The simulated cloud droplet effective radius, cloud radiative forcing, and precipitation rate, which relate to the aerosol indirect effect, are in reasonable agreement with satellite observations. The model results indicate that a decrease in the cloud droplet effective radius by anthropogenic aerosols occurs globally, while changes in the cloud water and precipitation are strongly affected by a variation of the dynamical hydrological cycle with a temperature change by the aerosol direct and first indirect effects rather than the second indirect effect itself. However, the cloud water can increase and the precipitation can simultaneously decrease in regions where a large amount of anthropogenic aerosols and cloud water exist, which is a strong signal of the second indirect effect. The global mean radiative forcings of the direct and indirect effects at the tropopause by anthropogenic aerosols are calculated to be -0.1 and -0.9 W m , respectively. It is suggested that aerosol particles approximately reduce 40% of the increase in the surface air temperature by anthropogenic greenhouse gases on the global mean. Copyright 2005 by the American Geophysical Union. -2

DOI： 10.1029/2004JD005029

全球気候モデルにネスティングした地域気候モデルによる21世紀のアジアの水循環変動予測

大楽浩司, 江守正多, 野沢徹

水工学論文集 49 397 - 402 2005年

出版者・発行元：Japan Society of Civil Engineers

We have developed a new regional climate model based on the Regional Atmospheric Modeling System (RAMS), and conducted present and future Asian regional climate simulations nested in the CCSR/NIES Atmospheric General Circulation Model (AGCM). The general simulated features of the AGCM and some regional phenomena such as orographic precipitation, which were notappeared in the outcome of the AGCM simulation, were successfully produced by the nested regionalclimate model. Annual mean precipitation, evapotranspiration and surface runoff are projected to increase in a lot of Asian regions. Those indicate faster and stronger hydrological cycles. There is growing apprehension that the risk of floods will increase under the global warming and the associated hydrological changes such as the intensification of convective precipitation in summer, the reduction of snow cover in winter, and earlier snow melting in spring.

DOI： 10.2208/prohe.49.397

Future climate change: Implications for Indian summer monsoon and its variability 査読

M Lal, T Nozawa, S Emori, H Harasawa, K Takahashi, M Kimoto, A Abe-Ouchi, T Nakajima, T Takemura, A Numaguti

CURRENT SCIENCE 81 ( 9 ) 1196 - 1207 2001年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：CURRENT SCIENCE ASSN

The broad climatological features associated with the Asian monsoon circulation, including its mean state and intraseasonal and interannual variability over the Indian subcontinent, as simulated in the CCSR/NIES coupled A-O GCM in its control experiment are presented in this paper. The model reproduces the seasonal cycle as well as basic observed patterns of key climatic parameters, in spite of some limitations in simulation of the monsoon rainfall. While the seasonality in rainfall over the region is well simulated and the simulated area-averaged monsoon rainfall is only marginally higher than the observed rainfall, the peak rainfall is simulated to be about two-thirds of the observed precipitation intensity over central India.
The transient experiments performed with the model following the four SRES 'Marker' emission scenarios, which include revised trends for all the principal anthropogenic forcing agents for the future suggest an annual mean area-averaged surface warming over the Indian subcontinent to range between 3.5 and 5.5 degreesC over the region during 2080s. During winter, India may experience between 5 and 25% decline in rainfall. The decline in wintertime-rainfall over India is likely to be significant and may lead to droughts during the dry summer months. Only a 10 to 15% increase is projected in area-averaged summer monsoon rainfall over the Indian subcontinent. The date of onset of summer monsoon over India could become more variable in future.

その他リンク： http://orcid.org/0000-0003-1745-5952

Simulation of Future Aerosol Distribution, Radiative Forcing, and Long-Range Transport in East Asia : 査読

Takemura Toshihiko, Nakajima Teruyuki, Nozawa Toru, Aoki Kazuma

Journal of the Meteorological Society of Japan. Ser. II 79 ( 6 ) 1139 - 1155 2001年

記述言語：英語出版者・発行元：Meteorological Society of Japan

Distribution of aerosol concentrations, optical properties, and wet deposition fluxes are simulated for the next fifty years using an aerosol transport model coupled with an atmospheric general circulation model. Treated species are sulfur dioxide, and all the main tropospheric aerosols, i.e., carbonaceous(black and organic carbons), sulfate, soil dust, and sea salt. We especially pay attention to distributions of anthropogenic carbonaceous aerosols, sulfate aerosols, and sulfur dioxide. The simulation uses the Special Report on Emissions Scenarios(SRES)of the Intergovernmental Panel on Climate Change(IPCC)as the future emission scenarios of anthropogenic pollutants. Simulated results suggest that carbonaceous aerosols continue to increase over industrial and densely populated regions for the next five decades, whereas sulfate aerosols decrease around Europe and North America. The aerosol single scattering albedo in the future is, therefore, calculated to become small gradually in the mid-and high-latitudes of the Northern Hemisphere. Sulfate aerosols and sulfur wet deposition fluxes are, on the other hand, simulated to increase only over East Asia. Black carbon and sulfate aerosols around Japan in 2050 are simulated to be two or three times as large as those in 2000 with one of the SRES scenarios. Hence this suggests that pollutants originating from the East Asian continent can seriously affect the atmospheric quality in Japan in the next several decades.

DOI： 10.2151/jmsj.79.1139

その他リンク： http://dl.ndl.go.jp/info:ndljp/pid/10611945

Coupled ocean-atmosphere model experiments of future climate change with an explicit representation of sulfate aerosol scattering 査読

Seita Emori, Seita Emori, Toru Nozawa, Ayako Abe-Ouchi, Atusi Numaguti, Masahide Kimoto, Teruyuki Nakajima

Journal of the Meteorological Society of Japan 77 ( 6 ) 1299 - 1307 1999年1月

記述言語：英語出版者・発行元：日本気象学会

The transient response of a coupled ocean-atmosphere model to increasing concentrations of greenhouse gases and sulfate aerosols, is investigated with an explicit representation of aerosol scattering. Experiments with an implicit representation of aerosol scattering, through the modification of surface albedo with the same parameter values as used in previous climate projections, are also conducted for comparison. The indirect effect of aerosol is yet to be included. As suggested by previous radiation computation studies, the estimated radiative forcing due to the direct effect of sulfate aerosol is significantly smaller with the explicit representation, than with the implicit one. A principal source of the overestimation by the implicit method is the neglect of the dependence of aerosol scattering on near-surface humidity. The projected surface air temperature change due to the addition of sulfate aerosols is considerably smaller in magnitude especially over dry regions with the explicit method, than with the implicit one. It is also suggested that the change in the Asian summer monsoon precipitation due to an increase in sulfate aerosols is particularly sensitive to the representation of sulfate aerosol scattering.

DOI： 10.2151/jmsj1965.77.6_1299

Spectral anisotropy in forced two-dimensional turbulence on a rotating sphere 査読

Toru Nozawa, Shigeo Yoden

Physics of Fluids 9 ( 12 ) 3834 - 3842 1997年12月

担当区分：筆頭著者掲載種別：研究論文（学術雑誌）出版者・発行元：AIP Publishing

The datasets on the forced two-dimensional turbulence on a rotating sphere obtained in our recent direct numerical simulations were analyzed to study the spectral anisotropy due to the rotation of the sphere. The results were also compared with those previously obtained in some β-plane experiments to assess the β-plane approximation of the rotating sphere. Owing to the effect of rotation the upward energy cascade ceases around a characteristic total wavenumber nβ at which the linear “β-term” is comparable to the nonlinear Jacobian term. The energy density of zonal components (m=0) is dominant in the range of n≲nβ while the energy is very small in an airfoil-shaped region at the lower edge in the wavenumber space (m,n). Anisotropic distribution of the energy is also found in the high wavenumber region n≳nβ; the energy density decreases as the zonal wavenumber m increases. The flow field in the spherical geometry is projected on some tangential planes from the equator to the poles to compare the spherical results directory with previous β-plane experiments. The energy distribution becomes anisotropic to have dominant zonal components as the local “β-effect” increases (or the tangential plane is put closer to the equator). In the case on equatorial tangential planes, the region in which the energy density is very small shows a dumbbell shape indicating strong anisotropy; this is the first confirmation of the recent finding by Vallis and Maltrud in full spherical geometry.

DOI： 10.1063/1.869518

Formation of zonal band structure in forced two-dimensional turbulence on a rotating sphere 査読

Toru Nozawa, Shigeo Yoden

Physics of Fluids 9 ( 7 ) 2081 - 2093 1997年7月

担当区分：筆頭著者掲載種別：研究論文（学術雑誌）出版者・発行元：AIP Publishing

A series of numerical experiments on the forced two-dimensional turbulence on a rotating sphere were done to investigate the formation processes of zonal band structures and their sensitivity to two experimental parameters of the rotation rate and the forcing wave number. A high-resolution barotropic full spherical model of T199 truncation is used with a homogeneous and isotropic formulation of the vorticity forcing function. Three different flow regimes are obtained and one of them is a new regime previously unknown. In the cases of no rotation, a very large flow pattern is obtained as a result of the upward energy cascade to the lowest wave number. The pattern irregularly fluctuates with time. A zonal band structure that consists of alternating easterly and westerly jets becomes dominant with an increase in the rotation rate. The alternating jets, which are robust and persistent, are already formed to be discernible in the very early stage of the time integration. The width of the jets decrease and the number of those increases as the rotation rate increases. The upward cascade of the disturbance energy ceases owing to the effect of rotation around a characteristic wave number nβ at which the “β term” is comparable to the nonlinear Jacobian term. Scale separation between the scale of cascade arrest and the forcing scale allows a systematic alignment of the vortices elongated by the shear in the zonal mean zonal flow, and such an alignment maintains the zonal band structure. When the forcing wave number is small and the rotation rate is large, the band structure is confined in high latitudes yielding a circumpolar vortex with a strong easterly jet, and a wavy structure dominates in middle and low latitudes. This is the new flow regime that is found in this study. Any systematic phase relation is not established in these latitudes because the phases are scrambled by the forcing due to the insufficient scale separation, therefore, the alternating zonal band structure does not emerge.

DOI： 10.1063/1.869327

傾斜対流実験のフラクタル次元解析査読

野沢徹, 酒井敏, 余田成男

天気 40 ( 11 ) 843 - 853 1993年11月

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