太阳辐射日变化对夏季风模拟特征的影响

利用６０°Ｓ－６０°Ｎ范围，有海气耦合但无海流的七层原始方程模式，做了有无太阳辐射日变化的对比试验。结果表明：准定常的平均季风系统的形势受太阳辐射日变化的影响不明显，其主要的影响可能来自海陆和地形分布。但是模式中包含太阳辐射日变化后，大气上下层季风系统强度的模拟得到了改善。太阳辐射日变化在很大程度上影响降水的分布形势，在没有太阳辐射日变化的试验中，大陆内部的降水大大减少，而沿海地区的降水增加。土壤温度和湿度的变化与降水变化对应良好。降水增加和减少的地区呈波状分布。至于对季风发展的影响，结果表明在季风发展的初期，太阳辐射日变化可加快其发展。因此，太阳辐射日变化的引入，可使平衡态较早达到     

9000年前古气候的数值模拟研究

本文用大气物理所的全球大气环流模式模拟了9000年前一月份和七月份的古气候.得出:北半球夏季由于地球轨道参数的变化引起的比现在多7％的太阳辐射使得温度升高了,尤其是高纬地区,海陆对比的加强又增强了季风,季风区域降水增加了;而冬季因为太阳辐射在北半球减少了7％,温度变低了.这些结果与现有的古气候证据相一致,并与其他模拟结果进行了较详细的比较,还作了进一步的讨论.     

用一个耦合的全球格点大气环流模式-植被模式模拟中全新世气候变化

用一个耦合的全球格点大气环流模式－植被模式模拟中全新世的气候变化，模拟试验中考虑了地球轨道参数的变化，而其他强迫条件均取成现今值。结果表明，耦合的模式能够模拟出较今强的大尺度夏季风，特别是亚洲－非洲季风，而其他季节和区域的变化值一般都比较小。季风环流和季风降水都大幅度地增大了。结果还显示，耦合模式模拟的大尺度季风系统的变化同单纯大气环流模式模拟的结果非常相似，但是，在非洲北部季风区耦合模式模拟的降水和温度变化较单纯大气模式模拟的值要大，而且，耦合模式模拟的冬季降温值要比单纯大气模式模拟的结果小。     

印度夏季季风的研究

随季节而变化的季风环流是与每年亚洲大陆的加热和冷却作用相联系的,它构成了大气环流的最重要的大尺度特征。印度季风是指印度洋地区低层大气的盛行风向一年之内作两次逆转变化,这主要是北部的大陆和南部的海洋之间的加热不同所造成的。“季风”一词不仅用于印度洋上的盛行风系统,而且还与非洲和南亚的热带和赤道地区的天气现象相联系。亚洲夏季季风则意味着6—9月期间的降雨。印度夏季季风与亚洲许多国家的国计民生息息相关。以往由于印度洋地区资料缺少,使研究工作受到限制。最近通过“季风试验”(MONEX)和“全球大气研究计划第一次全球试验”(FGGE),这方面的研究正在取得新的进展。     

BCC_CSM1.0模式对20世纪降水及其变率的模拟

应用国家气候中心气候系统模式 (BCC_CSM1.0),在给定温室气体、太阳常数、硫酸盐气溶胶、火山灰等外强迫数据的条件下,对19世纪末到20世纪气候进行模拟。对降水模拟结果的检验表明:BCC_CSM1.0模式能够模拟出全球降水的基本气候状态、季节变化、季节内振荡、年际变化等特征。模拟结果显示:与CMAP及CRU观测分析资料相比基本一致,全球陆地降水在过去一个多世纪中存在上升趋势。同时,模式也存在不足和需要改进之处:模拟降水的时空分布与观测不一致;我国东部地区的雨带季节转变较观测偏快;主要雨带位置较观测偏西、偏北;夏季青藏高原东北侧有虚假的降水中心;热带季节内振荡较实际偏弱;降水年际变率较观测略大,主要发生在降水较明显的热带。BCC_CSM1.0模式模拟的全球陆地降水以及欧亚、亚洲、中国大陆 (中国东部、江南、华北等地区) 平均降水与近105年由观测所得的CRU资料基本一致,但多数地区比观测略偏低。模拟的全球陆地、中国东部、江南、华北等地区的降水趋势也与CRU资料一致;模拟的全球陆地降水在过去105年中有明显的上升趋势,与CRU资料相比,上升趋势更强,但在欧亚、亚洲、中国范围内模拟的降水趋势与观测有一定的差异。     

青藏高原能量和水循环试验研究--GAME/Tibet与CAMP/Tibet研究进展

“全球能量水循环之亚洲季风青藏高原试验研究”(GAME/Tibet)和“全球协调加强观测计划(CEOP)亚澳季风之青藏高原试验研究”(CAMP/Tibet)的加强期观测和长期观测已经进行了8年多,并取得了大量的珍贵资料和一系列研究成果。本文首先介绍了GAME/Tibet和CAMP/Tibet试验的科学目标、研究内容、试验区概况、仪器设置、观测时间及资料采集的情况,然后介绍了这两个试验在地气相互作用的观测研究、观测与卫星遥感资料相结合估算区域陆面过程参数和对青藏高原陆面过程的数值模拟及藏北高原降水的时空变化等方面的研究进展,同时指出了目前试验研究中所存在的问题并提出了解决问题的途经。     

亚洲夏季风爆发的深对流特征

文中应用ＮＯＡＡ卫星反演的１９８０～１９９５年候平均对流层上部水汽亮温（ＢＴ）资料、向外长波辐 射（ＯＬＲ）资料和美国ＮＭＣ全球分析８５０　ｈＰａ风资料与美国ＣＭＡＰ降水资料作了对比分析，发现Ｂ Ｔ能够较好地反映中低纬度地区的深对流降水，偏南风场辐合区与深对流降水有比较一致的 关系，而ＯＬＲ不能反映热带外地区的对流降水。ＢＴ资料所具有的这一特征可以应用于亚洲夏 季风爆发过程的深对流特征分析。ＢＴ描述深对流的临界值是２４４　Ｋ。亚洲季风区是全球深对 流季节变化范围和强度最大的地区。赤道外地区的夏季风爆发可以定义为来自热带地区深对 流的季节扩张。中南半岛上的夏季风对流发生在南海夏季风爆发之前。华南前汛期深对流是 中低纬系统相互作用的结果。第２８候，南海夏季风的突然爆发在降水、风场和卫星反演 的深对流特征上都有明确的反映。南海夏季风爆发后，印度夏季风对流由南向北逐渐爆发， 青藏高原东侧和中国东部沿海的夏季风对流向北推进早于中国中部地区。     

全球季风槽

根据先前的研究总结出,全球有22个地形槽,其中只有3个行星尺度的季风槽和6个半岛尺度的季风槽。全球季风系统是由行星尺度季风槽和半岛尺度季风槽组成的。活动于热带北太平洋、热带北大西洋和热带南印度洋的赤道辐合带是太阳辐射随季节强迫下位置发生变化的行星尺度季风槽。半岛尺度季风槽起源于区域海陆地形和随季节变化的海陆热力对比和干湿(降水)转换。在北半球夏季,亚洲-西北太平洋地区受到4个半岛尺度季风槽和1个行星尺度季风槽的影响。其他2个半岛尺度的季风槽位于南非和印度尼西亚-西澳大利亚地区。     

亚洲的全球变化问题

本文分为三个部分,首先论述本世纪,尤其是近几十年来,全球变化在亚洲的主要表现,然后分析引起亚洲变化的主要驱动因子,特别是与全球气候变化相关的亚洲季风的变化和人类的作用;然后主要依据全球气候模式（ＧＣＭ）的结果评估全球增暖条件下亚洲未来２０～５０年的变化。最后讨论了ＧＣＭ模式在区域尺度模拟和评估上的不确定性,提出应将研究亚洲季风系统中大气圈－生物圈相互作用和亚洲地区土地利用／土地覆盖变化这两个科学问题,列入亚洲地区ＩＧＢＰ的研究,并和全球变化的三大国际科学计划ＩＧＢＰ、ＷＣＲＰ和ＨＤＰ中的一系列核心计划相结合     

青藏高原增暖对东亚夏季风的影响——大气环流模式数值模拟研究

20世纪50年代以来,随着全球海表面温度年代际变化和全球变暖现象的出现,东亚夏季风降水和环流场也出现相应的年代际变化。是什么原因引起这个长期的变化趋势？研究表明青藏高原增暖可能是导致东亚夏季风年代际变化的重要因子之一。为了能够更好地理解青藏高原地表状况对下游东亚季风的影响,作者使用德国马普气象研究所大气环流模式（ECHAM）进行一系列数值试验。在两组敏感性试验中,通过改变高原上的地表反照率从而达到改变地表温度的目的。数值试验结果表明:青藏高原增暖有助于增强对流层上层的南亚高压、高原北侧西风急流和高原南侧东风急流以及印度低空西南季风;与此同时,东亚地区低层西南气流水汽输送增强。高原增暖后降水场的变化表现为:印度西北部季风降水增加,长江中下游以及朝鲜半岛梅雨降水增多;在太平洋副热带高压控制下的西北太平洋地区和孟加拉湾东北部,季风降水减少。对数值模拟结果的初步诊断分析表明:在感热加热和对流引起的潜热加热相互作用下,南亚高压强度加强,东亚夏季低层西南季风增大、梅雨锋降水增强,高原东部对流层上层的副热带气旋性环流增加,以及对流层低层的西太平洋副热带高压增强。另外,在青藏高原增暖的背景下,孟加拉湾地区季风降水减弱。本项研究有助于更好地理解东亚夏季风年代际变化特征和未来气候变化趋势。     

The general circulation model precipitation bias over the southwestern equatorial Indian Ocean and its implications for simulating the South Asian monsoon

Most of current general circulation models (GCMs) show a remarkable positive precipitation bias over the southwestern equatorial Indian Ocean (SWEIO), which can be thought of as a westward expansion of the simulated IO convergence zone toward the coast of Africa. The bias is common to both coupled and uncoupled models, suggesting that its origin does not stem from the way boundary conditions are specified. The spatio-temporal evolution of the precipitation and associated three-dimensional atmospheric circulation biases is comprehensively characterized by comparing the GFDL AM3 atmospheric model to observations. It is shown that the oceanic bias, which develops in spring and reduces during the monsoon season, is associated to a consistent precipitation and circulation anomalous pattern over the whole Indian region. In the vertical, the areas are linked by an anomalous Hadley-type meridional circulation, whose northern branch subsides over northeastern India significantly affecting the monsoon evolution (e.g., delaying its onset). This study makes the case that the precipitation bias over the SWEIO is forced by the model excess response to the local meridional sea surface temperature (SST) gradient through enhanced near-surface meridional wind convergence. This is suggested by observational evidence and supported by AM3 sensitivity experiments. The latter show that relaxing the magnitude of the meridional SST gradient in the SWEIO can lead to a significant reduction of both local and large-scale precipitation and circulation biases. The ability of local anomalies over the SWEIO to force a large-scale remote response to the north is further supported by numerical experiments with the GFDL spectral dry dynamical core model. By imposing a realistic anomalous heating source over the SWEIO the model is able to reproduce the main dynamical features of the AM3 bias. These results indicate that improved GCM simulations of the South Asian summer monsoon could be achieved by reducing the springtime model bias over the SWEIO. Deficiencies in the atmospheric model, and in particular in the convective parameterization, are suggested to play a key role. Finally, the important mechanism controlling the simulated precipitation distribution over South Asia found here should be considered in the interpretation and attribution of regional precipitation variation under climate change.     

Global Monsoon Changes under the Paris Agreement Temperature Goals in CESM1(CAM5)

Based on experiments with the Community Earth System Model, version 1(Community Atmosphere Model, version 5)[CESM1(CAM5)], and an observational dataset, we found that CESM1-CAM5 is able to reproduce global monsoon(GM)features, including the patterns of monsoon precipitation and monsoon domains, the magnitude of GM precipitation(GMP,the local summer precipitation), GM area(GMA), and GM percentage(the ratio of the local summer precipitation to annual precipitation). Under the Paris Agreement temperature goals, the GM in CESM1-CAM5 displays the following changes:(1)The GMA is ambiguous under the 1.5℃ temperature goal and increases under the 2.0℃ temperature goal. The increase mainly results from a change in the monsoon percentage.(2) The GM, land monsoon and ocean monsoon precipitation all significantly increase under both the 1.5℃ and 2.0℃ goals. The increases are mainly due to the enhancement of humidity and evaporation.(3) The percentages of GM, land monsoon and ocean monsoon feature little change under the temperature goals.(4) The lengths of the GM, land monsoon and ocean monsoon are significantly prolonged under the temperature goals.The increase in precipitation during the monsoon withdrawal month mainly accounts for the prolonged monsoons. Regarding the differences between the 1.5℃ and 2.0℃ temperature goals, it is certain that the GMP displays significant discrepancies.In addition, a large-scale enhancement of ascending motion occurs over the southeastern Tibetan Plateau and South China under a warming climate, whereas other monsoon areas experience an overall decline in ascending motion. This leads to an extraordinary wetting over Asian monsoon areas.     

青藏高原及其周边地区降水的水汽来源变化研究进展

近几十年来,随着全球气候变暖,青藏高原降水整体呈现增加趋势,气候暖湿化趋势明显;与此同时,位于青藏高原东南缘的中国西南地区整体上呈现暖干化趋势,干旱事件频发。探讨青藏高原及其周边地区降水的水汽来源变化、揭示降水趋势性变化的原因已经成为当前研究热点。本文评述了近年来青藏高原降水的水汽来源研究,重点关注青藏高原变湿、西南地区变干的水汽来源变化原因以及青藏高原南北水汽来源差异,讨论了尚未解决的科学问题,展望了未来研究方向。现有研究表明,青藏高原以西的西风带控制区蒸散发贡献的水汽整体呈现减少趋势,青藏高原以南和以东的季风控制区蒸散发贡献的水汽整体呈现增加趋势,上述水汽源区贡献变化导致了青藏高原及其周边不同区域降水趋势性变化的差异。展望未来,水汽来源分析的模型和数据需要进一步验证及减少不确定性,青藏高原下垫面和蒸散发变化对周边地区降水的影响机制研究有待加强,全球变化与青藏高原降水水汽来源变化的关系尚需深入分析。     

The role of ocean thermodynamics and dynamics in Asian summer monsoon changes during the mid-Holocene

Studies of climate change 6,000 years before present using atmospheric general circulation models (AGCMs) suggest the enhancement and northward shift of the summer Asian and African monsoons in the Northern Hemisphere. Although enhancement of the African monsoonal precipitation by ocean coupling is a common and robust feature, contradictions exist between analyses of the role of the ocean in the strength of the Asian monsoon. We investigated the role of the ocean in the Asian monsoon and sought to clarify which oceanic mechanisms played an important role using three ocean coupling schemes: MIROC, an atmosphere–ocean coupled general circulation model [C]; an AGCM extracted from MIROC coupled with a mixed-layer ocean model [M]; and the same AGCM, but with prescribed sea surface temperatures [A]. The effect of “ocean dynamics” is quantified through differences between experiments [C] and [M]. The effect of “ocean thermodynamics” is quantified through differences between experiments [M] and [A]. The precipitation change for the African and Asian monsoon area suggested that the ocean thermodynamics played an important role. In particular, the enhancement of the Asian monsoonal precipitation was most vigorous in the AGCM simulations, but mitigated in early summer in ocean coupled cases, which were not significantly different from each other. The ocean feedbacks were not significant for the precipitation change in late summer. On the other hand, in Africa, ocean thermodynamics contributed to the further enhancement of the precipitation from spring to autumn, and the ocean dynamics had a modest impact in enhancing precipitation in late summer.     

INFLUENCES OF DIURNAL CHANGE OF SOLAR RADIATION ON SIMULATED PROPERTIES OF SUMMER MONSOON*

Comparative experiments with and without the diurnal change of solar radiation are made in this paper by use of an air-sea coupled 7-layer primitive equation modeling system in a zonal domain between 60°S and 60°N.The results show that the quasi-stationary patterns of the mean monsoon circulations are not evidently affected by the diurnal change of solar radiation.The main influences may come from the land-sea distribution and the orography.However,the inclusion of the diurnal change of solar radiation into the model system may improve the intensities of the simulated monsoon circulations both at the high and the low levels.It can influence the distributive pattern of precipitation to a larger extent.Without the diurnal change,precipitation in the interior of land would decrease and in the coastal regions it would increase.The changes of the soil temperature and the soil moisture are fairly correspondent to that of precipitation.The areas with increasing precipitation and the areas with decreasing precipitation are distributed in the wave form.As to the influences on the monsoon development,the results indicate that the diurnal change of solar radiation can speed up the development of the monsoon in the early stage.Therefore,the inclusion of the diurnal change of solar radiation can make the model equilibrium state to reach earlier.     

Sensitivity of the Asian summer monsoon to the horizontal resolution: differences between AMIP-type and coupled model experiments

A set of experiments forced with observed SST has been performed with the Echam4 atmospheric GCM at three different horizontal resolutions (T30, T42 and T106). These experiments have been used to study the sensitivity of the simulated Asian summer monsoon (ASM) to the horizontal resolution. The ASM is reasonably well simulated by the Echam4 model at all resolutions. In particular, the low-level westerly flow, that is the dominant manifestation of the Asian summer monsoon, is well captured by the model, and the precipitation is reasonably simulated in intensity and space appearance. The main improvements due to an higher resolution model are associated to regional aspects of the precipitation, for example the Western Ghats precipitation is better reproduced. The interannual variability of precipitation and wind fields in the Asian monsoon region appears to be less affected by an increase in the horizontal resolution than the mean climatology is. A possible reason is that the former is mainly SST-forced. Besides, the availability of experiments at different horizontal resolution realized with the Echam4 model coupled to a global oceanic model allows the possibility to compare these simulations with the experiments previously described. This analysis showed that the coupled model is able to reproduce a realistic monsoon, as the basic dynamics of the phenomenon is captured. The increase of the horizontal resolution of the atmospheric component influences the simulated monsoon with the same characteristics of the forced experiments. Some basic features of the Asian summer monsoon, as the interannual variability and the connection with ENSO, are further investigated.     

Global monsoons in the mid-Holocene and oceanic feedback

The response of the six major summer monsoon systems (the North American monsoon, the northern Africa monsoon, the Asia monsoon, the northern Australasian monsoon, the South America monsoon and the southern Africa monsoon) to mid-Holocene orbital forcing has been investigated using a coupled ocean–atmosphere general circulation model (FOAM), with the focus on the distinct roles of the direct insolation forcing and oceanic feedback. The simulation result is also found to compare well with the NCAR CSM. The direct effects of the change in insolation produce an enhancement of the Northern Hemisphere monsoons and a reduction of the Southern Hemisphere monsoons. Ocean feedbacks produce a further enhancement of the northern Africa monsoon and the North American monsoon. However, ocean feedbacks appear to weaken the Asia monsoon, although the overall effect (direct insolation forcing plus ocean feedback) remains a strengthened monsoon. The impact of ocean feedbacks on the South American and southern African monsoons is relatively small, and therefore these regions, especially the South America, experienced a reduced monsoon regime compared to present. However, there is a strong ocean feedback on the northern Australian monsoon that negates the direct effects of orbital changes and results in a strengthening of austral summer monsoon precipitation in this region. A new synthesis is made for mid-Holocene paleoenvironmental records and is compared with the model simulations. Overall, model simulations produce changes in regional climates that are generally consistent with paleoenvironmental observations.     

Numerical experiments of the effects of initial desert moisture on the climate change

A numerical model with the p-sigma incorporated coordinate system and primitive equations is used to simulate the effect of initial soil moisture in desert areas on the climate change. The results show that the present deserts have a tendency to expand. When the initial soil moisture in the desert regions increases, the desert areas will shrink but can not disappear. The small deserts may not remain any longer when there are sources of water vapour around. Both the land-sea contrast and the topography are the background conditions of the present desert distribution through the mechanism of the downdrafts and the rare precipitation over the desert regions. The increase of the initial desert soil moisture will weaken the summer monsoon circulation and, consequently, the monsoonal precipitation.     

A possible role of solar radiation and ocean in the mid-Holocene East Asian monsoon climate

An atmospheric general circulation model (AGCM) and an oceanic general circulation model (OGCM) are asynchronously coupled to simulate the climate of the mid-Holocene period. The role of the solar radiation and ocean in the mid-Holocene East Asian monsoon climate is analyzed and some mechanisms are revealed. At the forcing of changed solar radiation induced by the changed orbital parameters and the changed SST simulated by the OGCM, compared with when there is orbital forcing alone, there is more precipitation and the monsoon is stronger in the summer of East Asia, and the winter temperature increases over China. These agree better with the reconstructed data. It is revealed that the change of solar radiation can displace northward the ITCZ and the East Asia subtropical jet, which bring more precipitation over the south of Tibet and North and Northeast China. By analyzing the summer meridional latent heat transport, it is found that the influence of solar radiation change is mainly to increase the convergence of atmosphere toward the land, and the influence of SST change is mainly to transport more moisture to the sea surface atmosphere. Their synergistic effect on East Asian precipitation is much stronger than the sum of their respective effects.