中全新世时期我国西南风气候季节演变的数值模拟结果分析

COUPLED SIMULATION RESULT OF SEASONAL EVOLUTION OF SOUTHWESTERLY WIND CLIMATE OVER EASTERN CHINA IN MID-HOLOCENE

利用CCSM3海洋-大气耦合模式模拟结果,探讨了中全新世(6kaB.P.)我国东部西南风气候的季节演变规律。结果表明,6kaB.P.我国东部南风最早于1月出现在20°～25°N区域,此后逐渐增强,到秋季转为北风。随着南风强度从春季到夏季的强化,南风同时向北和向南扩展。我国东部西风于1月出现在23°～34°N,之后也逐渐加强,并于6～8月发生北跳,9月开始转为东风。这些特征与当今西南风爆发进程相类似,不过也存在一些显著差异,尤其是在夏季。与当今气候相比,6kaB.P.强南风建立时间偏晚,夏季我国东部西南风强度偏强,南风向北扩展更明显。这与6kaB.P.东亚大陆和西太平洋之间更大的热力差异以及西南涡和西太平副热带高压的加强有关。研究还表明6kaB.P.西南风异常可进一步导致我国东部夏季降水增加和雨带偏北。

The mid-Holocene（6kaB. P. ）is a typical interglacial period in which climate was largely different from that of the present day. By far a number of mid-Holocene climate simulations have been established, most of which however were completed mainly by atmospheric general circulation models and a few by coupled ocean-atmosphere general circulation models. Moreover, the simulations focused on the summer mean climate status while paid less attention to the evolution of the East Asian monsoon. Therefore, the present study is motivated to investigate the seasonal evolution of southwesterly wind climate over Eastern China in the mid-Holocene, through analysis of the simulation result of an ocean-atmosphere coupled model CCSM3. The results show that the southerly wind during 6kaB. P. firstly began over Eastern China within 20° -25°N in January. It was gradually strengthened afterwards and switched to the northerly wind in autumn. Concurrent with the development of its intensity, the southerly wind extends northward and southward from spring to summer. Similar to the change of the southerly wind direction,there is a reversal of the zonal wind direction over Eastern China as well. The westerly wind during 6kaB. P. appeared over Eastern China within 23°～ 34°N in January,and then was reinforced gradually. It shifted northward during June to August and was substituted by the easterly wind in September. To the north of 34°N,there is no seasonal reversal of the zonal wind direction, with the westerly wind blowing all year round. Such features resemble those of the present climate. However, there also exists significant difference between 6kaB. P. and the present,especially in summer. Compared to the present climate,the onset time of the strong southerly wind over Eastern China during 6kaB. P. seemed to be a litter later. Furthermore, the southwesterly wind over Eastern China was much stronger and its extension was further northward during the summer time. The difference between 6kaB. P. and the present can be attributed to the change of the land-sea thermal contrast,the southwest vortex and Western Pacific subtropical high. In comparison with the present day, the largescale thermal difference between the East Asian continent and the Western Pacific as well as the intensity of the southwest vortex and the Western Pacific subtropical high during 6kaB. P. was obviously stronger, favoring an increase of the local southwesterly wind. Besides, the Western Pacific subtropical high located to the north made the southwesterly wind expand further northward during 6kaB. P. In addition, accompanied with the evolution of the southwesterly wind during 6kaB. P., the low-level convergence gradually intensified and marched northward from winter to summer,resulting in an increase of the local rainfall and a shift of the major rain belt. Nevertheless,the preliminary result was obtained from a coupled ocean-atmosphere general circulation model. Additional analysis based on more coupled ocean-atmosphere general circulation models are needed in the future work. Further studies with more integrated geologic data and high-resolution regional climate models will yield additional information about 6kaB. P. climate.