亚洲经、纬向海陆热力差异对东亚冬季风环流的影响

The zonal thermal difference between the East Asian continent（including Tibetan Plateau）and the West Pacific Ocean, and the meridional counterpart between Asia and its Southern ocean as well as the South China Sea jointly have great effects on the East Asian Winter Monsoon (EAWM) circulation, and thereby resulting in the complex winter climate variations in China. However, comparing with the previous studies mostly centered on the impacts of the zonal sea-land thermal contrast on the winter monsoon system, the research aiming at the effects of the meridional one is relatively less. Therefore, this project is mainly focused on the circulation difference resulted from these two thermal contrast. By a series of diagnostic analysis, the relationship between these two thermal differences and EAWM interannual variabilities, as well as the winter surface temperature variations in China will be understood, and the relative contribution of these two thermal differences to the EAWM circulation variations and the key influence mechanism on the surface temperature variations will be further revealed by some numerical simulations. Based on the above studies, a general winter monsoon index, which can describe much more variations characteristics of EAWM system members and well reflect the winter surface temperature variations in China, is to be put forward. The project results will help elucidate the EAWM formation mechanism and its variation characteristics, so as to provide some scientific basis for improving the monsoon climate predictions.

东亚地区既存在东亚大陆（包括青藏高原）与西太平洋的东西向海陆热力差异，又与南侧低纬西太平洋和南海形成南北向海陆热力对比，两种热力差异共同影响东亚冬季风的环流变化，从而对我国冬季气候异常造成影响。然而以往研究多是强调纬向海陆热力差异对冬季风系统的作用，针对经向海陆热力差异对冬季风的影响研究相对较少。本申请拟将这两种热力差异所导致的季风环流差异作为研究重点，通过诊断分析揭示两种热力差异与冬季风环流的年际变率及我国冬季地面气温变化的联系，通过数值模拟揭示两种热力差异对冬季风环流影响的相对贡献及对我国冬季地面气温影响的关键区和影响机制，并在此基础上定义一个能够综合反映东亚冬季风系统更多成员变化特征并能较好反映我国冬季气温变化的综合性指数。预期研究成果将有助于增进对东亚冬季风形成机制与变化机理的了解，进而为相关气候预测提供一些科学依据。

基于观测资料和再分析资料，本项目首先分析了中国冬季气温变化的显著模态以及与之相联系的前期影响因子。结果表明中国冬季地面气温变化主要受东亚冬季风环流影响，但又具有较强的局地性和复杂性。中国西北地区冬季气温变化与贝加尔湖秋季地表气温变化呈现显著的负相关，贝加尔湖区秋季偏暖（冷）有利于西北地区冬季偏冷（暖）。而中国东北地区冬季气温变化与蒙古高原的秋季地表气温变化密切相关，蒙古高原秋季暖（冷）的状况将有利于东北地区经历暖（冷）冬。这在一定程度上反映了秋季亚洲大陆雪盖变化导致的冬季局地热力差异变化对冬季亚洲气候的影响。秋季贝加尔湖地表气温的变化通过影响冬季对流层高层和地面西风异常，进而影响中国西北地区地表气温。蒙古高原前期秋季的地表气温异常通过调节东亚大槽的强度和位置对东北地区地表气温产生显著影响。对西南地区而言，其冬季气温变化与中国大陆的蒙古冷高压和阿留申低压的强弱变化关系密切，蒙古高压偏强（弱），阿留申低压偏弱（强）时，中国西南地区冬季气温偏低（高），表明亚洲大陆和西太平洋纬向海陆热力差异对中国西南地区冬季气温产生显著的影响。其研究成果增进了对中国不同区域冬季地面气温变化机理的了解。进一步地，对东亚季风环流季节转变与亚太热力场之间的联系及可能机理进行了研究，计算了全年逐候的亚太纬向热力差指数，结果表明其与赵平等人采用各季不同关键区的APO指数高度一致，但该指数（下称APTD指数）可用于确定热力场季节转变的时间点。发现用APTD指数确定的季节转变时间点能表征东亚大气环流冬季型和夏季型间的转变。并且该转变点的早晚与热带中东太平洋的海温异常有显著的正相关。研究成果增进了对东亚季风环流转变机理的认识，为短期气候预测提供了科学依据。