Full Reference List

Comparison of local precipitation-SST relationship between the observation and a reanalysis dataset.

Arakawa, O. and A. Kitoh (2004)

Geophys. Res. Lett., 31, L12206, doi:10.1029/2004GL020283.

Abstract.

We defined a grid-scale time-phase relationship between precipitation (PR) and underlying sea surface temperature (SST) as the local PR-SST relationship, and compared the spatial distribution of the relationship in the observation with that in a reanalysis dataset. An analysis using observed pentad mean data shows precipitation lagging SST for two pentads over large areas of tropical oceans. A reanalysis dataset, on the other hand, has a shorter time-phase difference between precipitation and SST than that in the observation and does not match the spatial distribution of the observed local PR-SST relationship over the tropical Indian Ocean and the tropical western Pacific. A reanalysis dataset may not capture the observed local PR-SST relationship in terms of either time-phase difference or spatial distribution because a numerical model in a data assimilation system uses SST as a lower boundary condition as well as the inhomogeneity of observations the system used.

Effects of mountain uplift on East Asian summer climate investigated by a coupled atmosphere-ocean GCM.

Kitoh, A. (2004)

J. Climate, 17, 783-802.

Abstract.

To study the effects of progressive mountain uplift on East Asian summer climate, a series of coupled general circulation model (CGCM) experiments were performed. Eight different mountain heights were used: 0% (no mountain), 20%, 40%, 60%, 80%, 100% (control run), 120%, and 140%. The land-sea distribution is the same for all experiments and mountain heights are varied uniformly over the entire globe.
Systematic changes in precipitation pattern and circulation fields as well as sea surface temperature (SST) appeared with progressive mountain uplift. In summertime, precipitation area moves inland on the Asian continent with mountain uplift, while the Pacific subtropical anticyclone and associated trade winds become stronger. The mountain uplift resulted in an SST increase over the western tropical Pacific and the Maritime Continent and an SST decrease over the western Indian Ocean and the central subtropical Pacific. There is a drastic change in the East Asian circulations with the threshold value at the 60% mountain height. With the mountain height below 60%, the southwesterly monsoon flow from the Indian Ocean becomes strong by uplift and transports moisture toward East Asia, forming the baiu rainband. With higher mountain heights, intensified subtropical trade winds transport moisture from the Pacific into the Asian continent.
In order to investigate how the SST change affected the results presented herein, additional experiments were performed with the same experimental design but with the atmospheric GCM (AGCM). A comparison between CGCM and AGCM experiments revealed that major features such as a shift in precipitation inland and an appearance of the baiu rainband by higher orography were reproduced similarly in both the AGCM and the CGCM. However, there was a qualitatively as well as quantitatively different feature. The anticyclonic circulation anomalies in the lower troposphere, which appeared by mountain uplift in the tropical western Pacific in the CGCM associated with lowered SST, fed more moisture over East Asia and resulted in a stronger baiu rainband in the CGCM than that in the AGCM. An extent of the monsoon westerly flow is regulated by competition between the Pacific subtropical anticyclone and the southwest monsoon. The confluence zone was located near the Philippines throughout the mountain uplift in the AGCM, but it shifted backward to the west via mountain uplift in the CGCM associated with simulated SST changes. Overall the CGCM showed a larger sensitivity to mountain uplift than the AGCM due to the SST changes, thus warranting an examination of the importance of air-sea coupling and a need for the use of coupled models for such sensitivity studies.


Precipitation SST

Figure

June mean precipitation (left) and SST (right) for the observations and for eight CGCM experiments with different mountain heights.

South and East Asian summer monsoon climate and variation in MRI coupled model (MRI-CGCM2).

Rajendran, K., A. Kitoh and S. Yukimoto (2004)

J. Climate, 17, 763-782.

Abstract.

Simulations of the major characteristics of the summer monsoon climate over South Asia, East Asia, and the western North Pacific by the new version of the Meteorological Research Institute coupled GCM (MRI-CGCM2) are analyzed. In addition to assessing the simulation of mean summer monsoon rainfall and its association with SST and basic circulation parameters, the model's performance in reproducing the seasonal variation, climatological onset, peak, withdrawal, and subseasonal variation of the monsoon is also studied.
The mean rainfall distribution and the maximum rainfall centers over South Asia and the western North Pacific, including the monsoon rainbelt over central India, though shifted southward of its observed position by about 5°, and the baiu rainband across Japan, are well simulated. However, the model underestimates the monsoon rainfall over southeast China. The biases in model mean rainfall are found to be associated with biases in wind, moisture convergence, and vertical stability of the atmosphere. The relationship between mean SST and organized convection in the model is close to the observations, with a propensity for deep convection increasing with an increase in SST above the threshold value. The simulated summer anomalies of SST and surface fluxes imply the dominance of the SST-wind-evaporation feedback system over most of the Indian and western Pacific Oceans on intraseasonal time scales. In addition, in the model, equatorial eastern Pacific SST anomalies strongly influence the Indian summer monsoon predominantly on biennial time scales. The model captures the basic monsoon seasonal cycle, onset, peak, and withdrawal over India and the western North Pacific across Japan. However, the simulation shows an early onset of the monsoon over mainland China and the early occurrence of peak rainfall over southeast China. The active-break spells in Indian monsoon rainfall and meridional propagations of rainbelts over India and the western North Pacific are realistically simulated. But, over southeastern China, the model is unable to simulate northward propagation of rainbelts, which contributes to the poor simulation of seasonal mean rainfall.

onset

Figure

Observed (Xie-Arkin) and simulated (MRI-CGCM2) onset dates of the rainy season based on the relative climatological pentad mean rainfall.

Monsoon low-frequency intraseasonal oscillation and ocean-atmosphere coupling over the Indian Ocean.

Rajendran, K., A. Kitoh and O. Arakawa(2004)

Geophys. Res. Lett., 31, L02210, doi:10.1029/2003GL019031.

Abstract.

The impact of coupled interaction over Indian Ocean on the monsoon low-frequency intraseasonal oscillation is investigated by analysing the simulations of MRI coupled general circulation model (CGCM) and its stand alone atmospheric version (AGCM). Composites of northward propagations constructed based on objective criteria show that the characteristics of CGCM simulated low-frequency intraseasonal oscillation are close to observation. In CGCM, the atmosphere impacts SST through wind, evaporation, and radiation anomalies and the ocean modulates atmospheric convection through intraseasonal SST fluctuations. But, in AGCM, SST acts only as a boundary forcing without any significant contribution from atmosphere in modulating SST. As a result, the simulated low frequency oscillation lacks many of the important features associated with its amplitude, phase and life-cycle. These results warrant the use of coupled GCMs for simulating and studying monsoon lowfrequency oscillation.

Effects of Large-Scale Mountains on Surface Climate - A Coupled Ocean-Atmosphere General Circulation Model Study

Kitoh, A. (2002)

J. Meteor. Soc. Japan, 80, 1165-1181.

Abstract.

Effect of mountain uplift on climate is investigated by a global coupled ocean-atmosphere general circulation model with an emphasis on surface temperature changes. Results of the no-mountain run (NM) are compared with those of the control run with the present-day orography (M). When the lapse-rate effect is eliminated, continent interior becomes warmer with mountain uplift because clouds become fewer and the surface drier due to decreased moisture transport. On the other hand, South Asia and East Asia become cooler because summer monsoon precipitation is stronger, which makes the land surface wetter and increases clouds. Over the ocean, the existence of orography has a role to reduce sea surface temperatures (SST), particularly over the subtropical eastern oceans. This occurs because evaporation is larger due to stronger trade winds and also less solar radiation reaches the surface due to more low-level clouds, both associated with stronger subtropical anticyclones in M. The subtropical gyre is stronger in M than in NM, and therefore, the Kuroshio Current is stronger in M. When the effect of the ocean general circulation is not included, the SST over the western north Pacific becomes much lower in M than in NM because of stronger cold air outbreak from Siberia in winter in M. Thus, the ocean circulation changes act to reduce the SST changes by heat transport.

大規模山岳の地表気候への効果-大気海洋結合大循環モデルによる研究-

鬼頭昭雄(2002)

気象集誌、80、1165-1181.

要旨

山岳の存在が地表温度などの気候に与える効果を、全球大気海洋結合大循環モデルの山岳無し実験（ＮＭ）と山岳有り実験（Ｍ）とを比較することで調べた。山岳があると標高差による気温変化があるのでこのlapse-rate効果を除くと、大陸内部では水蒸気輸送が少なく乾燥して雲量が少なく暖かくなる。一方南アジアや東アジアでは、夏季モンスーン降水量が多くなり地表面を湿らせ雲量を増加させるため、山岳がある方が地表気温は下がる。山岳の存在は東部亜熱帯域の海面水温を下げる役割もする。これは山岳があることによりモンスーンが強くなり亜熱帯高気圧が強化され、下層雲が多くなり地表に入射する日射量が減少することと強い貿易風で蒸発が増えるためである。亜熱帯ジャイアはＭランの方が強く黒潮も強い。海洋循環を含まない海洋混合層モデルで実験を行うと、シベリアからのコールドサージの影響で日本付近の海面水温はＭランで低くなるが、大気海洋結合大循環モデルでは海洋循環の変化により海面水温偏差は緩和されることが分かった。

Tropical Pacific climate at the Mid-Holocene and the Last Glacial Maximum simulated by a coupled ocean-atmosphere GCM.

Kitoh, A. and S. Murakami(2002)

Paleoceangraphy, 17(3), 1047, doi:10.1029/2001PA000724.

Abstract.

Simulations for the mid-Holocene (6,000 years before present: 6ka) and the last glacial maximum (LGM: 21ka) have been performed by a global ocean-atmosphere coupled GCM. After the initial spin-up periods, both runs were integrated for about 200 years. For 6ka, the model shows an enhanced seasonal variation in surface temperature and a northward shift of the African and the Indian summer monsoon rain area. Overall circulation features in the tropics correspond to a strong Walker circulation state with negative sea surface temperature (SST) and precipitation anomalies in the central Pacific, and positive precipitation anomalies over the Indian and Australian monsoon regions. It is noted that there is about a 0.35°C cooling of the global mean SST. In contrast to the 6ka result, the simulated tropical climate anomaly at 21ka corresponds to a weak Walker circulation state. The simulated LGM SST decrease is about 2°C over the tropical western Pacific. It is larger (about 5°C) over the Caribbean Sea. This SST anomaly is in broad agreement with the observed proxy data. Interestingly, the model simulates a warmer than present SST over the subtropical Pacific. This may be related to a weaker subtropical anticyclone due to weakened monsoon circulation at the LGM.


6ka 21ka

Figure

Annual mean anomalies for (left) 6ka and (right) 21ka. (a) SST and ground temperature, (b) precipitation, and (c) surface wind.

ヒマラヤ・チベット山塊による気候システムへの影響

鬼頭昭雄(2002)

月刊地球、24、310-315

要旨

　ヒマラヤ・チベット山塊などの大規模山岳は、大気の流れに対する障壁となる力学的効果と、熱源となる熱力学的効果を通して、全球の気候システムやモンスーンに影響を与えている。その影響は大気のみならず、海にもおよんでいる。

Effect of Orography on Land and Ocean Surface Temperature

A. Kitoh (2001)

Present and Future of Modeling Global Environmental Change: Toward Integrated Modeling, Eds., T. Matsuno and H. Kida, TERRAPUB, pp. 427-431

A simulation of the Last Glacial Maximum with a coupled atmosphere-ocean GCM

Kitoh, A., S. Murakami and H. Koide (2001)

Geophys. Res. Lett., 28, 2221-2224

Abstract.

A simulation of the Last Glacial Maximum (LGM) climate has been performed by a global coupled atmosphere-ocean general circulation model (AOGCM). Two simulations are conducted for the LGM with different initial conditions: one with the present-day initial condition and the other with a pre-conditioning of fresh water flux over the North Atlantic. After more than 200 year integration both LGM simulations attained a similar quasi-equilibrium state. The global mean surface air temperature dropped 3.9 C and precipitation decreased 11% compared to the present day simulation. The sea surface temperature dropped 1.7 C in the tropics, with larger decreases in the Atlantic than in the Indo-Pacific. There is a region with warmer than present sea surface temperatures over the subtropical eastern Pacific. The thermohaline circulation in the North Atlantic in the LGM simulation is slightly stronger than in the present day simulation.

Figure

Differences between the LGM and the present-day simulation.

The Eddy-mean Flow Interaction and the Tropical-extratropical Interaction in a GCM and their Dependence on Model Horizontal Resolution

Moon J. -K., K. -J. Ha, A. Kitoh (1999)

Kor. J. Atmos. Sci., Korea , Vol. 2, 15-28

Abstract.

The eddy-mean flow interaction and the tropical-extratropical interaction are investigated by analyzing GCM simulations with different horizontal resolutions of 2 x 2.5 (high), 3 x 3.3 (medium), and 4 x 5 (low) latitude/longitude. The northern hemispheric winter circulation of simulation is more in agreement with observation when the horizontal resolution increases. The synoptic storm tracks in mid-latitudes are better simulated for a high resolution case than the lower resolution ones. The upper-level Rossby wave source term are compared to show the tropical- extratropical teleconnection in barotropical sense. The largest positive forcing of tropical heating is located at the exit region of the Asian Jet in all resolutions. But, the forcings for the high and medium resolution models have stronger intensity than the observation and seem to be associated with a strong vorticity gradient. In this study, the transient eddy forcing is estimated from the E-vector formulation, similar to an extended Eliassen-Palm (EP) flux. It is found that the eddy growth due to the strong zonal component of E-vector occurs over the exit region of the East Asian Jet (EAJ) and the North Atlantic Jet (NAJ). From the analysis of the growth of kinetic energy associated with the eddies during northern hemisphere winter (DJF season) at 200hPa, it is found that the low frequency fluctuations obtain their energy from the barotropic instability of the mean flow in the exit of EAJ and the entrance of NAJ and the Arabian Jet. As compared to the observation, the magnitude and the location of maximum values in each resolution model seem to have some biases. These results suggest that the interaction between the mean and the transient eddies is not much affected by the increase of model horizontal resolution.

気象研究所大気海洋結合モデルで再現された対流圏２年周期振動

小笠原範光、鬼頭昭雄、安成哲三、野田彰 (1999)

気象集誌　77巻, 1247-1270頁

Abstract.

南アジアモンスーン系において卓越する２年周期振動のメカニズムを、気象研究所全球大気･海洋結合モデルを用いて調べた。２年周期振動において、アジアモンスーンは熱帯太平洋の大気海洋結合系と、中緯度循環場との相互作用という２つのプロセスを通して中心的な役割を果たしている可能性が確認された。 モンスーンが強い年の春から夏の南アジアで相対的に活動な対流活動域は、秋から冬にかけてインドネシア付近へ南東進していく。この動きは気候値に見られる熱帯域での対流活動活発域の季節変化と良く一致しており、南アジアからオーストラリアのモンスーンが一連に強い状態となる事を示唆している。夏期に南アジアと熱帯太平洋間の東西循環偏差を通して形成された、熱帯太平洋における海面水温や対流活動偏差は、冬までの間に解消される傾向にある。 冬から春にかけての南アジア付近では、冬の間持続されるオーストラリアモンスーンに伴う対流活動偏差を熱源として、松野-Gillタイプの定常ロスビー波が形成される。モンスーンが強い年には南アジア上空で高気圧性循環、下層で低気圧性循環ができるため、寒気移流がより南まで入りやすい条件となっている。寒気移流は翌春まで持続し、これに伴い地上気温や上空の気温偏差は、春には中央アジアや南アジアで有意に冷たくなっている。このため大陸―海洋間の南北温度コントラストが弱められ、アジアモンスーンの強い年の翌年には逆にモンスーンは弱められると解釈できる。２年周期振動が年サイクルに見かけ上位相固定している理由は、春先の南アジアモンスーンの開始を通した、中緯度−熱帯間の相互作用が本質的な役割を果たしているためであると考えられる。モデル結果は、２年周期振動が陸面ーモンスーンー海洋結合系特有の変動であることを示唆しており、冬から翌春にかけてもたらされる、モンスーンと中緯度との相互作用が２年周期振動の維持において果たす役割を強調している。

Figure

気象研結合モデルの対流圏２年周期振動模式図

気象研究所大気海洋結合モデルでのENSO-モンスーン関係

鬼頭昭雄、行本誠史、野田彰 (1999)

気象集誌　77巻, 1221-1245頁

Abstract.

気象研究所大気海洋結合モデルでシミュレートした夏季アジアモンスーンの気候値とその年々変動のENSOとの関係について、観測値及び大気大循環モデル結果と比較して調べた。結合モデルで得られた海面水温は観測と異なるものの、両モデルのモンスーン循環は互いに似ている。下層風系や対流活動の季節変化で定義したモンスーン域の拡がりは観測とおおむね合っているが、モデルは西部太平洋での夏季の風系に欠点がある。 結合モデルは、観測されるENSOに関連する熱帯循環系の年々変動をよく再現しているが、モデルのエルニーニョが西偏していることによる違いが見られる。大気大循環モデルは境界条件として与えた海面水温に応答しており、太平洋では観測と合うものの、インド洋では観測と異なる。結合モデルでは大気と海洋の双方向の相互作用が表現できるものの、大気モデルでは与えた海面水温に応答するだけであることが違いをもたらしている。 結合モデルの結果によると、モデルのエルニーニョ時にインド夏季モンスーンが弱く、ラニーニャ時にモンスーンが強い傾向が見られ、観測と矛盾しない結果が得られた。強いモンスーンに先立つ春季の中央アジアでは有意に地面温度が高いが、積雪偏差の有意性は小さかった。

Figure

The leading multiple EOF mode for the simulated SST, precipitation and zonal wind at 850 hPa based on the June-August average data of the 150-year CGCM run.

On overestimation of tropical precipitation by an atmospheric general circulation model with prescribed SST

Kitoh, A. and O. Arakawa (1999)

Geophys. Res. Lett., 26, 2965-2968.

Abstract.

We investigate how an atmospheric general circulation model (AGCM) can reproduce the atmospheric aspects of climate, when the boundary condition are prescribed. The AGCM is integrated with sea surface temperature (SST) specified from an integration of a coupled general circulation model (CGCM). A systematic difference in the mean climate is found between the AGCM and the CGCM in the tropical Pacific. This difference is apparent when and where the local SST is warmest. In the CGCM, precipitation does not last long due to SST and cloud-radiation feedback. Precipitation in the AGCM, however, tends to persist longer. Results of this experiment imply that caution is needed when using an AGCM with boundary conditions derived from a CGCM for climate change studies.

Figure

Above: Hovmoller diagrams of (a) SST, (b) precipitation, (c) evaporation, (d) total heat flux, and (e) wind stress magnitude simulated by CGCM averaged for 14S-6S from October of yr4 to March of yr5. Bold solid lines denote the region where zonal gradient of SST is 0.1C per 1 longitude.
Below: Hovmoller diagrams of (a) precipitation, (b) evaporation, (c) total heat flux, and (d) wind stress magnitude from ensemble means simulated by AGCM. The AGCM is forced by SST obtained from CGCM.

MRI GCM-IIによるアジアの夏季モンスーンのシミュレーションに対する水平解像度の効果

Chandrasekar, A., D. V. Bhaskar Rao and A. Kitoh (1999)

Pap. Met. Geophys., 50, 65-80.

Abstract.

MRI GCM-IIを用いてアジアの夏季モンスーンのシミュレーションに対する水平解像度の効果を調べた。低（4ox5o）・中（3ox3.3o）・高（2ox2.5o）の３つの解像度でそれぞれ８年間の積分を行った。その結果、水平解像度の増加は海面気圧と降水量の分布パターンのシミュレーションを改善する効果をもたらした。高解像度モデルは観測と一致して熱低気圧とモンスーントラフをシミュレートしているが、低解像度モデルはインド北部に異常に強い熱低気圧をシミュレートした。また、高解像度モデルはベンガル湾と南インド洋の降水極大域とタリム盆地の乾燥域を再現している。一方で、アラビア海の降水極大域は低解像度モデルの方がよく再現していた。どの解像度でもモンスーン循環の強度は観測より弱いが、解像度を上げると下層モンスーン西風はさらに弱くなった。本研究の結果は、水平解像度の増加はアジアの夏季モンスーン循環の観測される特徴のシミュレーションの多くを改善するが、より悪くなる点もあり、モデルの物理過程の改良を伴う必要があることを意味している。

SST Variability and Its Mechanism in a Coupled Atmosphere/Mixed-Layer Ocean Model

Kitoh, A., T. Motoi and H. Koide (1999)

J. Climate, 12, 1221-1239.

Abstract.

Interannual SST variability in a coupled atmosphere-mixed layer ocean model is investigated. This model has no El Nino, but shows a large interannual SST variability in the tropical Pacific. The basin-scale feature of SST variation has some common characteristics shared with that obtained by a global ocean-atmosphere coupled GCM and observational data in the subtropical to the midlatitude Pacific. Both the latent heat flux and shortwave radiation have their roles in producing the SST anomalies. There is no large contrast in the total heat flux between the eastern and the western Pacific. However, their main components, the shortwave radiation and the latent heat flux, have a remarkable contrast between the cold tongue in the east and the warm pool region in the west. In the east, the ocean is warmed by shortwave and cooled by latent heat. This shortwave radiation is negatively correlated with low-level clouds. When the SST is warmer than normal in the eastern Pacific, there is less low-level stratus cloud cover and more shortwave radiation reaching the surface. In the western Pacific, the ocean is warmed by less evaporation due to weaker winds. When the ocean becomes warm, it is cooled by less shortwave radiation due to stronger activity in cumulus convection.

Figure

(a) Spatial pattern of the first EOF base don the 60-yr annual mean SST of the coupled atmosphere-mixed layer ocean model. Correlation coefficient of local SST on the time series of the first EOF are plotted. (b) Time series of the first EOF of SST.

夏季インドモンスーンに対する赤道インド洋海面水温偏差の影響

Chandrasekar, A. and 鬼頭昭雄 (1998)

気象集誌　76巻, 841-853頁

Abstract.

夏季の南アジアではインドと赤道インド洋の２個所に降水域が存在するが、一方が活発な時は他方で不活発となりやすい。また夏季インドモンスーンの弱い年にはインド洋の赤道の南で海面水温が正偏差となっている。このような海面水温偏差が夏季インドモンスーンに与える影響について、大気大循環モデルによるアンサンブル実験により調べた。実験の結果、海面水温偏差はインドで有意な応答を引き起こし、インドの降水量の減少とモンスーン循環の弱化をもたらした。負の海面水温偏差を与えた実験からは逆の結果が得られ、上記の関係が確認された。

CO2増加時の夏季アジアモンスーンの変化のシミュレーション

鬼頭昭雄、行本誠史、野田彰、本井達夫 (1997)

気象集誌　75巻, 1019-1031頁

要約

気候モデルによるチベット山塊の役割の評価

鬼頭昭雄 (1997)

地学雑誌, 106(2) 270-279.

Abstract.

Effects of mountains on climate are investigated by an atmospheric general circulation model coupled with a 50-m depth slab ocean model. A model simulation with the present-day orography reproduces most of the principal features of the observed climate. Another simulation without mountains (NM) is done and is compared with the one with mountains (M). Orography-originated stationary waves are separated from those induced by the existence of land-sea distribution. In northern winter, about two thirds of the stationary wave is explained by orography in this study. The wintertime subtropical jet in the upper troposphere in NM is more zonal and weaker than in M. The summertime subtropical jet in NM does not shift northward much and is located over China and Japan. The Asian summer monsoon in NM is substantially weaker than in M. Surface monsoon westerlies are weak, a rain belt stays south and the precipitation over India and China is less in the model without orography. On the other hand, the precipitation in the continental interior is large and the ground is wet in NM due to large moisture transport from the ocean. The global mean sea surface temperature in NM is warmer than in M. This occurs mainly from increased solar radiation into the ocean due to decreased lower tropospheric clouds over the subtropical eastern Pacific. Land surface temperature in NM is warmer than in M due to lapse-rate effect. However, the summertime surface temperature in Europe, Russia and Canada is cooler in NM than in M because ground surface in NM is wetter.

Mountain uplift and surface temperature changes

Kitoh, A. (1997)

Geophys. Res. Lett., 24, 185-188.

Abstract.

Mountain uplift significantly affects both sea surface temperature (SST) and land surface temperature. This was studied using a coupled atmosphere/mixed layer ocean model with and without mountains. The global mean SST dropped 1.4｡C with mountain uplift, mainly due to increased lower tropospheric clouds in the subtropical eastern Pacific. Increased clouds hinder solar radiation into the ocean and lower SST. The increased frequency of stratus incidence is related to subtropical anticyclones intensified by a strong temperature contrast between the continent and ocean in mountainous regions. Land surface temperature drops due to the lapse-rate effect. When this effect is eliminated, the continental interior does not become as cool with mountain uplift because clouds become fewer and the surface drier due to decreased moisture transport. Southern Asia becomes cooler because monsoon-induced precipitation wets the ground and increases clouds. Our result showed greater northern high latitude temperature changes than the previous study, indicating the importance of cloud-related feedback in paleoclimate modeling.

Figure

(a) Annually averaged surface temperature difference (deg C) between mountain and no-mountain runs. (b) As for (a) except for that temperature for the mountain run is adjusted by 6.5 K/km, the environmental lapse rate.

Interannual variability in the stratospheric-tropospheric circulation in a coupled ocean-atmosphere GCM

Kitoh, A., H. Koide, K. Kodera, S. Yukimoto, and A. Noda (1996)

Geophys. Res. Lett., 23, 543-546.

Abstract.

Relationships between the northern winter stratospheric and tropospheric circulations and the sea surface temperature (SST) simulated by a global coupled ocean-atmosphere general circulation model are investigated. Two modes are extracted for interannual variability of the zonal-mean zonal wind by an empirical orthogonal function analysis. The first mode is related with interannual variations of the stratospheric polar vortex. This mode has a significant correlation with the North Pacific SST through tropospheric circulation changes. The second mode is the variation of the tropospheric subtropical jet and is related with the simulated El Nino. Model results imply no strong relationship between El Nino and the polar vortex.

Figure

Simulated correlations between the time coefficients of (top) first and (bottom) second EOF modes of zonally averaged zonal wind and (left) 50 hPa height, (middle) 500 hPa height and (right) SST in DJF. Data for 70 winters are used. Contour intervals: 10 %.

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