孟加拉湾夏季季节内振荡的湿静力能分析

Budget Analysis of Moist Static Energy in Summertime Intra-seasonal Oscillations Over the Bay of Bengal

夏季期间大气季节内振荡(ISO)活跃于孟加拉湾区域,并存在显著的向北传播。采用1979-2016年ERA-Interim大气再分析资料,通过对典型ISO事件进行位相合成,揭示了夏季期间孟加拉湾湿静力能季节内变化的演变特征和控制机理。结果表明,ISO大气对流在向北传播期间伴随着显著的湿静力能累积(充电)和释放(放电)过程。其中,水汽主导的湿静力能水平平流是充电和放电的关键控制因素。水汽水平平流在对流层中高层和对流层低层的变异机理存在一定差异,在中高层主要取决于ISO扰动纬向风对低频水汽的纬向输送,在低层则主要取决于低频经向风对ISO扰动水汽的经向输送。

The northward-propagating intra-seasonal oscillations(ISOs) activate in the Bay of Bengal(BoB) during boreal summer. In this study, the intra-seasonal evolutions and controlling mechanisms of moist static energy(MSE) in the BoB are diagnosed based on ERA-Interim reanalysis data in 1979-2016. The ISO phase-dependent composite indicates that strong MSE recharge and discharge occurs during the ISO northward propagation in the BoB. A budget analysis of MSE further reveals that the recharge and discharge are primarily controlled by the moisture term associated with horizontal advection. In addition, it is noted that different physical processes dominate the horizontal moisture advection between the mid-upper and the lower troposphere. At mid-upper level, the horizontal moisture advection mainly depends on the transport of low-frequency moisture by intra-seasonal zonal wind. While at lower level, the horizontal moisture advection is mainly due to the transport of intra-seasonal moisture by low-frequency meridional wind.