华北地区“16·7”极端强降水事件之环流及扰动能量变化特征

2016年7月18—22日在华北地区发生了一次极端强降水事件，其中19—20日降水较为集中，20日降水最强。本文利用NCEP/NCAR再分析逐日风场资料和国家级地面气象站基本气象要素日值数据集，研究了本次事件的Rossby波活动及能量变化，结果表明：本次极端强降水事件持续时间约5 d，雨带呈西南—东北走向。华北地区受对流层中低层的气旋性异常环流和对流层上层反气旋性异常环流的控制，水汽则主要源于孟加拉湾和中国南海地区。发生极端降水期间，波扰动能量在对流层低层主要呈经向传播而在对流层上层呈纬向传播，对流层低层的波扰动能量对华北地区的影响比上层更为明显。涡动动能在华北地区的增强和维持主要是涡动非地转位势通量散度项、涡动有效位能和涡动动能的斜压转换项以及其他剩余部分与摩擦耗散引起的能量损耗之和的共同作用，涡动动能在19日增强、20日维持，随后减弱。涡动热量通量变化显示低层有暖湿空气向北输送，高层有干冷空气向南输送，支持了正压和斜压转换，而华北地区上空涡动动量通量的变化则使得基本气流中的涡动动能增强，这些变化影响到极端降水事件的发生发展。

Features of circulation and its related energetics of regional daily precipitation extreme event in North China on July 2016

An extreme heavy precipitation event occurred in North China from July 18 to 22, 2016, in which the precipitation was concentrated on July 19 and 20 and reached the strongest on 20. Based on NCEP/NCAR reanalysis and datasets of daily basic meteorological elements from China national meteorological stations,the precipitation characteristics, Rossby wave activity and energy changes of this event are investigated.This precipitation lasted for five days and the rain belt is in the direction of southwest to northeast. Results show that atmospheric conditions in North China are dominated by an anomalous cyclonic circulation in the middle and lower troposphere and an anomalous anticyclonic circulation in the upper troposphere, and the water vapor mainly originates from the Bay of Bengal and the South China Sea during the period of extreme heavy precipitation. Meanwhile, the wave disturbance energy in the lower troposphere mainly propagates in the meridional direction, while in the upper troposphere it propagates in the zonal direction.The influence of wave disturbance energy in the lower troposphere in North China is more effective than that in the upper troposphere.The enhancement and maintenance of eddy kinetic energy in North China are mainly due to the divergence of non-geostrophic eddy geopotential flux, the baroclinic conversion of energy from eddy effective potential energy to eddy kinetic energy, the dissipation caused by turbulence friction and other residuals. As a result, the vortex kinetic energy enhanced on 19, maintained on 20, and then weakened. The variation of eddy heat flux indicates that warm moist air is transported to the north in the low layer whereas dry cold air is transported to the south in the high layer, which consistent with the conversion between barotropic and baroclinic. Meanwhile, the variation of eddy momentum flux over the North China enhances the eddy dynamic energy in the basic airflow.