Eight Years of TRMM Data: Exploring Regional Mechanisms Behind the Diurnal Cycle

With the successful collection of eight years of data from the Tropical Rainfall Measuring Mission (TRMM) satellite, sampling has become sufficient to examine the diurnal cycle of rainfall and convective system morphology on a regional basis. Observations from the Precipitation Radar (PR), TRMM Microwave Imager (TMI), Visible and Infrared Scanner (VIRS), and Lightning Imaging Sensor (LIS) have been combined into a Precipitation Feature (PF) database that allows the diurnal cycle of convective system morphology to be examined in an objective sense.

Building on the study of Nesbitt and Zipser (2003), which examined continental scale variability in the diurnal cycle of TRMM PFs, this study will examine the diurnal cycle of archetypical PF characteristics on sub-continental scales, based on the increased sampling that the TRMM satellite's now-accrued eight-year record can provide. Beyond the “noon balloon” convection that occurs over many land areas, Nesbitt and Zipser (2003) showed that much of the observed spatial and temporal diurnal variability in rainfall is due to the life cycle of mesoscale convective systems (MCSs). Over the ocean, the question of which of radiative forcing, radiation-dynamics feedbacks, and surface interactions and are responsible for the observed early morning maximum of MCSs frequency, convective intensity, and rainfall remains an open one. Thus a major scientific goal is to establish the link between forcing and maintenance mechanisms for MCSs (i.e. sea breeze circulations, topography, synoptic forcing, gravity waves, cold pool propagation) and the resulting diurnal cycle. The TRMM PR, TMI, and VIRS observations will be examined in this context, along with a subset of cotemporaneous geostationary IR data that provides continuous sampling, to identify regionally coherent diurnal cycle modes such that these mechanisms can be elucidated.