研究者詳細 - 野沢　徹

論文 - 野沢　徹

分割表示 67 件中 1 - 20 件目／全件表示 >>

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

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