Contents lists available at ScienceDirect Atmospheric Research journal homepage: www.elsevier.com/locate/atmosres Seasonality in power law scaling of convective and stratiform rainfall with lightning intensity over Indian Monsoon regions B.A. Choudhury a,b , B.N. Goswami a, ⁎ , Yasmin Zahan a , P.V. Rajesh a a Cotton University, Guwahati 781001, India b Assam, University, Silchar, Assam 788001, India ARTICLE INFO Keywords: Lightning Flash Rainfall Power law relation Storm Top Height ABSTRACT The power law relationship between the rain (R T ) and lightning fash (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 signifcant 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 R T 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 ffth 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 fndings suggest that one threshold based lightning para- meterizations are inadequate and need to be generalized to include regional and seasonal diferences unraveled here. 1. Introduction Over the Indian monsoon region with its unique orography (Fig. 1), the climatological mean summer rainfall (Fig. 2a) has a signifcant west to east increasing gradient in the northern part with a center of maximum in the north-east India while the southern India has a north-south oriented maximum rainfall over west of the Western Ghats. The Indian summer monsoon rainfall (ISMR, June-September mean rainfall over land points of India) constituting about 80% of annual rainfall over the region is life line to one ffth of world's population residing over south Asia with its vagaries strongly linked with economy and food production in the region (Gadgil and Gadgil, 2006). A reliable forewarning of ISMR is, therefore, critical for the policymakers and farmers alike. While considerable advances have been made during the past century towards understanding of drivers of mean ISMR and its year-to-year variability (Webster et al., 1998; Gadgil, 2003; Goswami and Chakravorty, 2017), major gaps remain. One such area is how does the electrical felds formed during the rain producing clouds modify the rain formation and what infuence does it exert on the mean rainfall and on extreme rain events? The lightning fashes (LF) and electrical activity within clouds and rainfall are intimately linked through dynamical and microphysical processes (Soula, 2009). The updrafts asso- ciated with the clouds result in hydrometeors (i.e., ice, snow, graupel, cloud and rain droplets) drop size distributions (DSD) that through colli- sion-coalescence, condensation, deposition, riming and evaporation result in rainfall at surface (see Fig. S1). While most studies on lightning and rainfall have been associated with convective storms, especially deep convective systems (Takayabu, 2006), there is evidence that signifcant electrical activity and lightning are also associated with stratiform rain https://doi.org/10.1016/j.atmosres.2020.105265 Received 11 May 2020; Received in revised form 6 August 2020; Accepted 14 September 2020 Abbreviations: BoB, Bay of Bengal; CAPE, Convective Available Potential Energy; CI, Central India; IO, Indian Ocean; ITCZ, Inter-tropical Convergence Zone; JJAS, June-July-August-September (Monsoon); LF, Lightning Flash; LIS, Lightning Imaging Sensor; MAM, March-April-May (Pre-monsoon); MCS, Mesoscale Convective System; NASA, National Aeronautics and Space Administration; NEI, North-East India; PR, Precipitation Radar; R T , Total Rain; RDSD, Rainfall Drop Size Distribution; SST, Sea Surface Temperature; STH, Storm Top Height; TMI, TRMM Microwave Imager; TRMM, Tropical Rainfall Measuring Mission ⁎ Corresponding author at: Department of Physics, Cotton University, Guwahati 781001, Assam, India. E-mail address: bhupengoswami100@gmail.com (B.N. Goswami). Atmospheric Research 248 (2021) 105265 Available online 18 September 2020 0169-8095/ © 2020 Elsevier B.V. All rights reserved. T