2010年汛期长江中游对流降水日变化特征分析

A Characteristic Analysis on Diurnal Variations of Convective Rainfall Along the Yangtze River Middle Valleys in 2010 Flooding Season

利用2010年6月16日至7月31日每3 h一次的探空资料、逐小时地面加密观测和卫星云图黑体辐射亮温(TBB)等资料,对长江中游的对流降水及大气物理量的日变化特征进行了分析。结果发现:对流降水具有明显的日变化特征,降水在15时(01时)左右具有峰(谷)值。地面气象要素和大气探空物理量也具有明显的日变化特征。地面温度的日变化特征最为明显,平均日变化幅度约9℃,露点温度的日变化幅度不到1℃,相对湿度的日变化主要由温度日变化造成。地面温度日变化的空间分布受到地形的影响,白天(夜间)高地形区升温(降温)幅度较平原地区大。地形差异造成的温度梯度日变化可驱动地形性热力流,白天山峰(平原)地区为地形性辐合(辐散)热力流,夜间恰好相反。白天低层大气稳定度降低和对流有效位能增大,有利于热对流的发展;夜间抬升凝结高度降低、相对湿度升高和大气可降水量增大有利于清晨长生命史对流系统的发展。

Abstract： With hourly intensive surface observations, satellite remote-sensed temperature of black body （TBB） and 3-hourly radio-soundings, an analysis is carried out to investigate the diurnal changes of convective rainfall and atmospheric physical variables along the middle valleys of Yangtze River. The result are as follows： the convective rainfall is of obvious diurnal changes, with a rainfall maximum （minimum at 1500 BT （0100 BT）. The surface and sounding physical variables are also of clear diurnal changes. Th diurnal variation of surface temperature is the most obvious, with a mean diurnal range of 9℃, while th diurnal range of dew point temperature is only about 1℃. The diurnal change of relative humidity is mainl caused by the temperature diurnal variation. The spatial distribution of surface temperature diurnal changes is influenced by the topography. The temperature rising （dropping） in the mountainous areas is large than in the plain areas in the daytime （nighttime）. The diurnal change of temperature gradient due to tin topographic difference can drive topographically near-surface thermal flow. The convergence （divergence flows occur in the mountainous areas （plain areas） in the daytime, vice versa in the nighttime. The stabilty decrease in the lower atmosphere and the CAPE increase are beneficial to the afternoon thermal convection initiation in the daytime. The lowering of lifting condensation level （LCL）, the increase of relative humidity and the increase of air-column precipitable water vapor （PW） are favorable for the development of long-life early-morning convective systems in the nighttime.