Seasonality in power law scaling of convective and stratiform rainfall with lightning intensity over Indian Monsoon regions

Abstract

The power law relationship between the rain (RT) and lightning flash (LF) is useful for estimating rainfall over poorly gauged catchment areas of rivers over north-east India (NEI) and that between LF and storm top height (STH) is key to lightning parametrization in models. However, they are poorly constrained over the Indian monsoon region where potential for significant changes exists with large spatial variability of rainfall, strong land-ocean contrast, seasonality and contribution of stratiform to total rainfall. Using 16 years of TRMM-PR data and LIS data, here we examine the RT and LF relationship and between LF and STH during pre-monsoon and monsoon seasons over four regions, NEI, Central India (CI), Bay of Bengal (BoB) and Indian Ocean (IO). A stronger power law (exponent b = 0.71) during pre-monsoon than that during the monsoon season (b = 0.58) apply for convective rain over land (including BoB) while a weaker relationship is applicable for stratiform rain with b = 0.60, and b = 0.47 respectively. Over IO, the relationship is nearly identical for convective and stratiform rain with no seasonality (b ~ 0.4). A power law poorly represents the LF-STH relationship over land and fails over IO. A fifth power law is applicable only for pre-monsoon convective rain over land weakening to half in monsoon seasons (b = 2.48). For stratiform rain it is weaker with (b = 3.27) and (b = 1.67) for pre-monsoon and monsoon seasons respectively. Our findings suggest that one threshold based lightning parameterizations are inadequate and need to be generalized to include regional and seasonal differences unraveled here.