研究者詳細 - 野沢　徹

論文 - 野沢　徹

分割表示 67 件中 41 - 60 件目／全件表示 >>

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

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