初夏西北太平洋副高东西变动对中国南部降水东西差异的影响

西北太平洋副热带高压(以下简称副高)是影响中国气候的大尺度环流系统,为了进一步了解副高对中国气候的影响,本文利用站点观测资料和大气环流再分析资料,通过资料诊断分析和数值模拟方法,探讨了6月副高东西变动对中国南部降水的影响,以及影响副高东西变动的前期海洋因子.结果表明副高东西变动对中国西南和华南地区降水的影响明显不同:副高偏东有利于降水西南偏多而华南偏少,偏西则降水变化刚好相反.其原因与副高东西变化引起的环流差异有关,华南降水与副高东(西)变动时西太平洋地区副高西北侧的东北(西南)风异常以及东亚中低纬度地区异常经向波列的变化直接有关,而西南降水异常不仅与副高东西变动在东南亚地区引起的纬向风异常有关,与青藏高原大地形动力作用对副高北侧异常纬向风的变化也有十分密切的联系.此外,副高东西变动时影响西南和华南地区的水汽来源不同,影响西南的水汽主要来源于赤道印度洋80°E附近越赤道气流,而影响华南的水汽主要来源于副高南侧偏东气流从西北太平洋地区输送的水汽.进一步分析发现前期冬春季热带西北太平洋和赤道西太平洋海温变化的偶极差异与后期初夏副高东西变动有密切联系,冬春季西北太平洋暖海温和赤道西太平洋冷海温变化有利于后期初夏副高偏西,相反则有利于副高偏东,数值模拟结果在一定程度证实了资料诊断分析结果.

The influence of east-west displacement of Northwestern Pacific subtropical high on east-west difference of precipitation in southern China in early summer

The Northwest Pacific Subtropical High(hereinafter referred to as the subtropical high,NWPSH)is a large-scale circulation system affecting China climate.To further understand the impact of the NWPSH east-west movement on the China climate,based on the precipitation data of observational stations and re-analysis of atmospheric circulation data,the influence of this movement on precipitation in June in south China,as well as the ocean factors affecting the NWPSH are investigated by using diagnosis analysis and numerical simulation.The results show that the influence of the NWPSH east-west movement on precipitation in southwest China and South China is obviously different:the NWPSH westward movement is favorable for the precipitation to be more in Southwest China and less in South China,while westward movement is just the opposite.The reason for such a difference is related to the circulation variation caused by the NWPSH east-west movement.The northeast(southwest)wind anomaly in the northwest side of the NWPSH and the anomalous meridional wave train at the middle and low latitudes in East Asia are directly related to the precipitation variation in South China.However,the precipitation anomaly in southwest China is close related not only to the zonal wind anomaly caused by the NWPSH east-west movement in southeast Asia,but also to the influence of the dynamic action of the Tibetan Plateau on the zonal wind of the north side of the NWPSH.Otherwise,the source of water vapor in the southwest and south China is different when the NWPSH moves eastward or westward,and the water vapor in the southwest China comes mainly from the cross-equatorial flow near 80°E in the Indian Ocean,while the water vapor in the South China comes from the easterly flow of the south side of the NWPSH from the Northwest Pacific.The dipole-like Sea Surface Temperature Anomalies(SSAT)in the tropical northwest Pacific and in equatorial western Pacific in the early winter and spring is closely related to the NWPSH east-west displacement in sequent early summer.The warm SSTA in northwest Pacific and cold SSTA in the equatorial western Pacific are beneficial to the subsequent NWPSH movement westward and vice versa.The numerical simulation further proves the influence of dipole-like SSTA on the NWPSH east-west movement.