孟加拉湾西南季风与南海热带季风的气候特征比较

Comparison of climate features between the Southwest Summer Monsoon of the Bay of Bengal and the South China Sea Summer Monsoon

本文运用NCAR/NCEP再分析数据和APHRO_MA_V1003R1降水数据,对比分析了孟加拉湾西南季风和南海热带季风的气候特征异同以及对降水分布的影响,得到如下结论:(1)孟加拉湾西南季风比南海热带季风爆发更早、强度更强、持续时间更久、向北推进更北.(2)孟加拉湾西南季风建立过程缓慢,主要是索马里越赤道西南气流的逐渐加强和热带印度洋ITCZ(赤道辐合带)的逐渐北移;而南海热带季风建立过程迅速,主要是东亚大槽的一次替换过程伴随西太平洋副热带高压的突然东撤和热带西太平洋ITCZ的突然北跳.(3)孟加拉湾西南风纬向分量较强,季风建立前后主要变化在于偏西风的强度;而南海西南风经向分量较强,季风建立后风向突然逆转,东南风由于副高东撤而迅速被西南风取代.(4)孟加拉湾西南季风撤退较快,而南海季风则撤退较慢.(5)根据季风进程将夏季风期划分为季风发展期(5月)、强盛期(6—8月)和减退期(9—10月).其间对流活跃区的发展和推进、季风槽的位置以及对应降水区域均有明显差异.(6)在夏季风期,孟加拉湾和南海经度上分别存在着由ITCZ北抬引起的、在季风槽对流活跃区上升而在南北两侧下沉的、南北对称分布的季风经向次级环流.由于孟加拉湾和青藏高原强大热源的存在,孟加拉湾上升区南北跨度比南海的更大;孟加拉湾经圈环流更加稳定,而南海经圈环流的南北摆动更明显;孟加拉湾上升中心区比南海的偏北;在季风减退期,由于南海ITCZ撤退较慢,其上升区比孟加拉湾上升区偏北.

Adopting NCAR/NCEP reanalysis data and APHRO_MA_V1003R1 precipitation data, this paper compares and analyzes the similarities and differences of climate features and impacts on precipitation distribution between the Southwest Summer Monsoon （SSM） of Bay of Bengal （BOB） and the South China Sea Summer Monsoon （SCSSM）. The results show that. （1） Compared with SCSSM, the SSM of BOB establishes earlier and more intense, drives more northward, and its duration is longer. （2） The SSM of BOB establishes slowly because the Somali cross-equatorial flow is strengthened slowly and the Tropical Indian ITCZ （Inter-Tropical Convergence Zone） moves northward gradually. Whereas the SCSSM establishes quickly because of one time replacing process of East Asia Trough with sudden eastward enhancement of Western Pacific Subtropical High （WPSH） and sudden northward jump of Tropical Western Pacific ITCZ. （3） The zonal characteristics of BOB is stronger, and the main variation after monsoon establishment is the southwest wind strength~ but the meridional characteristics of SCSSM are stronger, reversal of wind direction exists after monsoon establishment, and the southeast wind is replaced quickly by southwest wind because of eastward enhancement of WPSH. （4） The enhancement of SSM of BOB is quick while that of SCSSM is slow. （5） According to the monsoon process, Summer Monsoon （SM） period is divided into following stages, development （May）, strengthening （June-August）, and declining （September-October）. In different periods, the development and movement of active convection areas, the positions of monsoon runs through and the corresponding precipitation areas have obvious differences. （6） In the SM period, monsoon meridional sub-circulations exist along the longitudes of BOB and SCS, respectively, which are distributed on south and north sides symmetrically, caused by northward movement of ITCZ, and ascend in the active convection region of monsoon trough and descends on south and north sides. Because of strong heat sources of BOB and the Tibetan Plateau, the meridional ascending span region of BOB is wider with north descending region north of the Plateau, while the descending region of SCS is more southerly. The meridional circulation of BOB is more stable and the meridional circulation of SCS swings in meridion ascending center region of BOB is more northerly than that SM, the ascending center region of BOB is more southerly SCS enhances slowly. direction is more obvious. The SCS. In the decreasing period of an that of SCS, because ITCZ of