WWLLN lightning and satellite microwave radiometrics at 37 to 183 GHz: Implications for thundercloud charging in the broad tropics

We investigate global atmospheric convection and thundercloud charging mechanisms using data from the World Wide Lightning Location Network (WWLLN) and passive microwave radiometer observations. The radiometric database is from the Tropical Rainfall Measuring Mission satellite (TRMM) Microwave Imager (TMI), and the Special Sensor Microwave Imager/Sounder (SSMIS) on the Defense Meteorological Satellite Program (DMSP) satellite F16. Radiometric frequency channels range from 37 to 183 GHz, allowing observations related to several types of precipitating hydrometeors and vertical updrafts. For the first time, measurements from a land-based lightning network are compared with satellite microwave radiometric signatures from multiple platforms on a global scale, thus expanding and complementing the capabilities of previous lightning/radiometer studies. WWLLN lightning rates and minimum radiometer brightness temperatures are compared for two northern and southern hemisphere summers (2009-2011) for the broad tropics. We find that: 1. the probability of cold brightness temperatures (therefore frozen hydrometeors) increases about tenfold in lightning producing systems compared with non-lightning producing systems, and 2. brightness temperatures decrease with increasing lightning rates for all frequency channels examined. These findings are generally independent of land, coast, and ocean regimes. However, the highest probability of cold brightness temperatures for non-lightning producing clouds is found over the ocean. The results generally support the noninductive thundercloud charging mechanism on a global scale for the tropics and subtropics.