我国青藏高原气候动力学研究的近期进展

文章回顾了我国在青藏高原气象学的基础上发展起来的青藏高原气候动力学研究的近期进展；指出了青藏高原“感热驱动气泵(SHAP)”在调制东亚季风及全球气候中的重要作用；在强调全球海陆分布所产生的“四叶型”加热L0SECOD激发出夏季副热带基本环流型的基础上指出高原的隆升增强了东亚季风的北伸；论述与青藏高原抬升相联系的高原负涡度源所激发的Rossby波对全球气候异常的影响，指出春季青藏高原的表面感热加热是造成东亚环流季节突变的重要原因，并导致亚洲夏季风首先在孟加拉湾东部地区爆发；还就进一步发展青藏高原气候动力学问题作了探讨。     

7月青藏高原大气热源空间型及其与东亚大气环流和降水的相关研究

对1958～1999年的7月份NCEP/NCAR再分析资料中青藏高原区域大气热源强度(整层气柱的总非绝热加热率)做旋转经验正交函数分析,结果表明该区域内大气热源强度的空间分布特征复杂,各地差异显著。前4个REOF型的加热中心位于高原东北部、高原西南部、克什米尔地区以及高原东南部地区上空。小波分析还表明各空间型都有2～4a的变化周期。文中计算了前4个RPC与东亚中、低空纬向风(U)、经向风(V)、纬向水汽通量(Q_u)、经向水汽通量(Q_v)的相关系数,并用这些相关系数构造矢量,进而分析其流场和水汽通量散度场,发现高原不同区域的大气加热异常所对应的东亚大气环流形势及降水也大不相同,由此表明,在研究高原加热对中国气候的影响时,应注意加热的空间分布特征。     

Influences of external forcing changes on the summer cooling trend over East Asia

Observations indicate a surface cooling trend during the East Asian summer in recent decades, against a background of global warming. This cooling trend is re-examined using station data from 1951 to 2007, and atmospheric general circulation model (AGCM) simulations are performed to investigate the possible influence of changes in external forcing. The numerical experiments are designed to investigate the effects of four types of external forcing: greenhouse gases (GHGs), Total Solar Irradiance (TSI), ozone, and the direct effects of aerosols. Results indicate that external forcing contributes to the cooling trend over East Asia. Furthermore, GHGs, and to a lesser degree the direct effects of aerosols, are the main contributors to the cooling trend. The possible linkages between the external forcings and the cooling trend are discussed.     

Barotropic Process Contributing to the Formation and Growth of Tropical Cyclone Nargis

This study reveals the barotropic dynamics associated with the formation and growth of tropical cyclone Nargis in 2008,during its formation stage.Strong equatorial westerlies occurred over the southern Bay of Bengal in association with the arrival of an intraseasonal westerly event during the period 22-24 April 2008. The westerlies,together with strong tropical-subtropical easterlies,constituted a large-scale horizontal shear flow,creating cyclonic vorticity and thereby promoting the incipient disturbance that eventually evolved into Nargis.This basic zonal flow in the lower troposphere was barotropically unstable,with the amplified disturbance gaining more kinetic energy from the easterly jet than from the westerly jet during 25-26 April. This finding suggests that more attention should be paid to the unstable easterly jet when monitoring and predicting the development of tropical cyclones.Energetics analyses reveal that barotropic energy conversion by the meridional gradient of the basic zonal flow was indeed an important energy source for the growth of Nargis.     

孟加拉湾深对流加热对东亚季风环流系统的影响

利用40年逐日NCEP/NCAR再分析资料、ReynoldsSST资料和R42L9GOALS模式,研究孟加拉湾深对流加热对东亚副热带季风环流系统的影响及其与ENSO的关系。结果表明:孟加拉湾东岸季风于26候开始爆发,其深对流加热的旋转经验正交函数(REOF)分析表明,其激发的东传Rossby波在中高纬度地区具有相当正压结构。数值试验证实孟加拉湾降水增多,其东侧南海到长江以南区域降水明显减少。分析发现季风环流强度指数极小值和Walker环流强度指数极大值的出现对SSTA转折均具超前性,因此,季风环流的变化对预报ElNino减弱或LaNina结束及SSTA变化趋势具有一定的指示意义。     

2003年夏季梅雨期一次强气旋发展的位涡诊断分析

通过位涡诊断和回推轨迹分析, 对2003年夏季梅雨期间一次强江淮气旋的发展过程进行了研究。结果表明: 气旋发展初期, 非绝热加热在气旋的低层发展中起了主要作用, 随后由于高层水平平流的增强, 通过垂直平流使高低层大值位涡耦合在一起, 从而使气旋迅速发展。从中、 高、 低层对位涡柱形成所起的作用来看, 低层主要是非绝热加热, 中层是垂直平流, 而高层主要是水平平流; 从构成气旋的气流来说, 在气旋迅速发展阶段, 低层主要以西南暖湿气流为主, 高层 (500 hPa以上) 主要以沿急流轴下降的高层干冷气流和对流层底层流向气旋东北部并迅速上升的暖湿气流为主。高低层冷暖空气的相互作用主要发生在600 hPa及以上层次, 因凝结加热引起的垂直运动通过垂直平流可能在冷暖气流相互作用和上下大位涡的垂直耦合中发挥了重要作用。     

江南春雨的时空分布

江南春雨是东亚独特的天气气候现象,已有充分证据表明,它是青藏高原高大地形的动力和热力强迫的结果,但目前其时空分布还不明确.NCEP/NCAR环流及感热资料气候平均分析表明:在3月第1候(全年第13候),高原主体和高原东南部的感热加热、高原东南侧西南风速、江南春雨区西南风速和江南春雨区雨量都提升到一个新的水平,标志着江南春雨的建立;在5月第3候(全年第27候)以后,高原东南部的感热加热、高原东南侧西南风速、江南春雨区西南风速和江南春雨区雨量都迅速减小,对流层中低层南海副高脊线由南倾转北倾,江南雨带中心南移至南海,南海季风爆发,标志着江南春雨期的结束.因此,将江南春雨的建立和终结时间定为第13候和第27候比较适当.资料分析和数值敏感性试验表明,江南春雨期对流层低层冷暖空气的交汇区在30°N附近,但江南春雨雨带的位置和强度明显受南岭、武夷山脉地形的影响:山脉地形能阻挡抬升冷暖空气,加强锋生,增强降水,使雨带中心位置与山脉主轴分布重合.因此,江南春雨的空间范围包括长江中下游(30°N)以南、110°E以东的中国东南部地区.     

Revisiting Asian monsoon formation and change associated with Tibetan Plateau forcing: I. Formation

Numerical experiments with different idealized land and mountain distributions are carried out to study the formation of the Asian monsoon and related coupling processes. Results demonstrate that when there is only extratropical continent located between 0 and 120°E and between 20/30°N and the North Pole, a rather weak monsoon rainband appears along the southern border of the continent, coexisting with an intense intertropical convergence zone (ITCZ). The continuous ITCZ surrounds the whole globe, prohibits the development of near-surface cross-equatorial flow, and collects water vapor from tropical oceans, resulting in very weak monsoon rainfall. When tropical lands are integrated, the ITCZ over the longitude domain where the extratropical continent exists disappears as a consequence of the development of a strong surface cross-equatorial flow from the winter hemisphere to the summer hemisphere. In addition, an intense interaction between the two hemispheres develops, tropical water vapor is transported to the subtropics by the enhanced poleward flow, and a prototype of the Asian monsoon appears. The Tibetan Plateau acts to enhance the coupling between the lower and upper tropospheric circulations and between the subtropical and tropical monsoon circulations, resulting in an intensification of the East Asian summer monsoon and a weakening of the South Asian summer monsoon. Linking the Iranian Plateau to the Tibetan Plateau substantially reduces the precipitation over Africa and increases the precipitation over the Arabian Sea and the northern Indian subcontinent, effectively contributing to the development of the South Asian summer monsoon.     

The Flexible Global Ocean-Atmosphere-Land system model, Spectral Version 2: FGOALS-s2

The Flexible Global Ocean-Atmosphere-Land System model, Spectral Version 2 (FGOALS-s2) was used to simulate realistic climates and to study anthropogenic influences on climate change. Specifically, the FGOALS-s2 was integrated with Coupled Model Intercomparison Project Phase 5 (CMIP5) to conduct coordinated experiments that will provide valuable scientific information to climate research communities. The performances of FGOALS-s2 were assessed in simulating major climate phenomena, and documented both the strengths and weaknesses of the model. The results indicate that FGOALS-s2 successfully overcomes climate drift, and realistically models global and regional climate characteristics, including SST, precipitation, and atmospheric circulation. In particular, the model accurately captures annual and semi-annual SST cycles in the equatorial Pacific Ocean, and the main characteristic features of the Asian summer monsoon, which include a low-level southwestern jet and five monsoon rainfall centers. The simulated climate variability was further examined in terms of teleconnections, leading modes of global SST (namely, ENSO), Pacific Decadal Oscillations (PDO), and changes in 19th–20th century climate. The analysis demonstrates that FGOALS-s2 realistically simulates extra-tropical teleconnection patterns of large-scale climate, and irregular ENSO periods. The model gives fairly reasonable reconstructions of spatial patterns of PDO and global monsoon changes in the 20th century. However, because the indirect effects of aerosols are not included in the model, the simulated global temperature change during the period 1850–2005 is greater than the observed warming, by 0.6°C. Some other shortcomings of the model are also noted.     

冬季中高纬500hPa高度和海表温度异常特征及其相关分析

用旋转主分量（ＲＰＣ）方法，分析１９４８年到１９８８年４０个冬季的中高纬５００ｈＰａ高度场以及全球海表温度异常（ＳＳＴＡ）场的最主要的时空分布特征。然后通过交叉相关来讨论海气的同期相关特征。结果显示，冬季中高纬５００ｈＰａ高度场最明显的异常型分别是太平洋北美型（ＰＮＡ），西太平洋型（ＷＰ），西大西洋型（ＷＡ）以及东大西洋欧亚型（ＥＡＥＵ）。冬季ＳＳＴＡ最明显的区域是赤道东太平洋（ＥＥＰ）和赤道大西洋（ＥＡＬ）。其次是中纬度东北太平洋（ＮＥＰ）及两大洋西部（ＮＷＰ和ＮＷＡ）。中高纬度海气之间有很好的相关。与中高纬度５００ｈＰａ高度场ＰＮＡ型明显相关的是中高纬度东北太平洋（ＮＥＰ）和赤道东太平洋（ＥＥＰ）的ＳＳＴＡ。前者的强相关中心在中高纬；后者的强相关中心在中低纬。而与ＷＡ型明显相关的是中高纬度北大西洋的ＳＳＴＡ。中高纬度海气之间最强的相关在海气异常对应的空间位置上。而且这种区域性或邻域性的海气相关呈正相关，暖ＳＳＴＡ对应于正高度异常，冷ＳＳＴＡ对应于负高度异常