WWLLN lightning and passive satellite microwave data at 37 to 183 GHz: Deep convection in the global broad tropics and tropical cyclones

We investigate deep atmospheric convection in the global broad tropics, including case studies of tropical cyclones. The database used in this investigation combines real-time lightning and radiometric observations. The lightning data are from the World Wide Lightning Location Network (WWLLN). The brightness temperature data are 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 convection intensity. We study the relationships between lightning, convection, and brightness temperatures derived from all channels and differences in the brightness temperatures of the three 183 GHz channels. These 183 GHz brightness temperatures differences are caused by cloud ice above the water vapor emission levels in the atmosphere scattering the outgoing microwave radiation, as suggested by several previous studies.

For the broad tropics, we find that: (1) lightning occurrence is related to brightness temperature depressions for ice-scattering in all channels, as expected; and (2) the 183 GHz channels are successfully used to identify deep and shallow convection over land, coast and ocean. But, whereas high probabilities of lightning occurrence are observed for both intense and relatively weak convective systems over land, the lightning occurrence over the ocean is associated mostly with more intense convection. This study has also helped to further quantify lightning and 183 GHz brightness temperatures as indicators for deep convection for future geostationary lightning imagers and the recently launched Global Precipitation Measurement satellite.

We apply these broad tropics results to our investigation of intensity change and evolution of tropical cyclones. Our presentation culminates with case studies of tropical cyclones using WWLLN and satellite radiometer data.