研究者詳細 - 野沢　徹

論文 - 野沢　徹

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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

CiNii Article

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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.

Web of Science

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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

CiNii Article

CiNii Books

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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

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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

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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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