WWLLN lightning and satellite microwave radiometrics at 37 to 183 GHz: thunderstorms in the broad tropics†

We investigate lightning strokes and deep convection through the examination of cloud-to-ground (CG) lightning from the World Wide Lightning Location Network (WWLLN) and passive microwave radiometer data. Microwave channels at 37 to 183.3GHz are provided by 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. The present study compares WWLLN stroke rates and minimum radiometer brightness temperatures (Tbs) for two Northern Hemisphere and Southern Hemisphere summers (2009-2011) in the broad tropics (35 degrees S to 35 degrees N). To identify deep convection, we use lightning data and Tbs derived from all channels and differences in the Tbs (Tbs) of the three water vapor channels near 183.3GHz. We find that stroke probabilities increase with increasing Tb depressions for all frequencies examined. Moreover, we apply methods that use the 183.3GHz channels to pinpoint deep convection associated with lightning. High lightning stroke probabilities are found over land regions for both intense and relatively weak convective systems, although the TMI 85GHz results should be used with caution as they are affected by a 7km gap between the conical scans. Over the ocean, lightning is associated mostly with larger Tb depressions. Generally, our results support the noninductive thundercloud charging mechanism but do not rule out the inductive mechanism during the mature stages of storms. Lastly, we present a case study in which lightning stroke rates are used to reconstruct microwave radiometer Tbs.