中国东部夏季降水年际变化与同期东海潜热通量的关系

The relationship between inter-annual variations of summer precipitation in eastern China and latent heat flux in East China Sea

利用1985～2008年OAflux3、NCEP\NCAR再分析资料与中国大陆东部108个站点的降水资料,应用回归和合成方法,分析了中国东部夏季降水的年际变化与同期东海及邻近海域潜热通量变异的关系。结果表明:东海及邻近海域(以下称东海)夏季潜热通量年际变化显著的区域位于东海区域,为与同期中国东部降水密切相关的关键区域。当东海的潜热通量偏高(低)时,中国东部长江以南地区上空盛行偏东北(西南)风异常,这将不(有)利于水汽由南向北的输送,从而可能使到达长江中下游流域及以北地区的水汽偏少(多);并且,长江中、下游流域为下沉(上升)气流和低层水汽辐散(辐合)正异常,对应降水偏少(偏多);华南地区为上升(下沉)气流和低层水汽辐合(辐散)正异常,对应降水偏多(偏少)。分析结果还表明,东海的潜热通量可通过影响东亚大气环流而成为引起中国东部夏季汛期降水年际异常的重要原因之一。

Based on the OAFlux3, the NCEP/NCAR reanalysis data for the period of 1985--2008 and the daily data of summer precipitation at 108 observational stations of eastern China, the relationship between the inter- annual variations of summer precipitation in eastern China and the latent heat flux anomalies in the East China Sea （ECS） are analyzed by using the composite and the linear regression analysis methods. The mechanism of summer precipitation anomalies in eastern China caused by the latent heat flux in ECS is also further analyzed from the perspective of atmospheric zonal and meridional circulation and water vapor transport in East Asian area. In order to focus on the inter-annual timescles, the long-term trend in the variations of laten heat flux in ECS, summer precipitation in eastern China and atmospheric circulation over East Asia have been removed in this study. The analyzed results show that the latent heat flux displays strong inter-annual variations signal in ECS and is closely related to summer precipitation in eastern China. When the latent heat flux in ECS is above （below） normal in summer, an anomalous anticyclonic （cyclonic） circulation appears over the northwest Pacific and the northeasterly （southwesterly） anomalies appear over eastern China, which are unfavorable （favorable） for the northward transportation of water vapor and result in more （less） water vapor in South China and less （more） water vapor in the middle and lower reaches of the Changjiang River and north areas. Furthermore, the atmospheric zonal and meridional circulations will be manifested as a downward （upward） motion with a divergence （convergence） in low level and a convergence （divergence） in upper level can appear over the middle and lower reaches of the Changjiang River, which may result in less （more） summer rainfall. While in South China, the atmospheric zonal and meridional circulations will be manifested as upward （downward） anomaly and convergence （divergence） at low levels, which may result in more （less） summer rainfall. The variations of atmospheric zonal and meridional circulation and water vapor transportation over East Asia caused by the latent heat flux anomalies in ECS could lead to the precipitation anomalies in the above mentioned area. It is suggested that the abnormal change of the＇latent heat flux in ECS may be one of the most important factors for the abnormal of summer rainfall in East China on the inter-annual timescales.