A 6-Year Cloud-to-Ground Lightning Climatology and Its Relationship to Rainfall over Central and Eastern China

The cloud-to-ground (CG) lightning climatology and its relationship to rainfall over Central and Eastern China is examined, using 32 million CG lightning flashes data and TRMM (Tropical Rainfall Measuring Mission) measurements during a 6-yr period of 2008-2013. Results show substantial spatial and temporal variations of flash density across China. Flash counts are the highest (lowest) in summer (winter) with the lowest (highest) proportion of positive flashes. CG lightning over Northern China (NC) is more active only in summer, whereas in winter CG lightning is more active only in the middle and lower reach of Yangtze River basin (YRB). The highest CG lightning density exceeding 9 flashes km^(-2) yr^(-1) and more than 70 CG lightning days yr-1 are found in the northern Pearl River Delta region, followed by the Sichuan Basin, the Yangtze River Delta and the southeastern coast in that order (Fig. 1). A comparison of the convective rainfall climatology indicates similar patterns along the coastal regions. However, high flash density centers are not correlated to large rainfall centers. It is found that monthly convective rainfall is peaked in May or July, but the highest flash density appears in August. An analysis of the diurnal cycles shows a dominant CG lightning peak in late-afternoon hours for all the regions, with a secondary CG lightning peak near midnight during the warm season for SBM and NC, but double convective rainfall peaks, i.e., a higher one in the afternoon and the other in the morning hours over Southern China (SC) and YRB. The Sichuan Basin and its surrounding mountain areas (SBM) that is dominated by a late-night to early morning rainfall peak. An analysis of the convective and stratiform rainfall from the TRMM data indicates that the proportion of stratiform rainfall over YRB and SBM increases from the late night to early morning hours, and equals closely to that of convective rainfall with a distinct peak during the early morning hours. This nocturnal rainfall tendency is opposite to that of lightning activity. All these results suggest the important roles of surface heating and local topography in triggering deep convection, and the different roles of short- vs. long-lived mesoscale convective systems and stratiform rainfall in determining the diurnal cycles of CG lightning and rainfall. In general, higher-frequency thunderstorm but lower-flash-density days occur over mountainous regions due to the development of short-lived afternoon storms, whereas higher-flash-density days, typically associated with nocturnal thunderstorms, appear over the North China Plain and Sichuan Basin. During the monsoon season less flashes are generated over the plain and basin areas in the late night to morning hours when hourly rainfall peaks.