Using gauge and radar data from TRMM ground validation sites to determine the diurnal rainfall cycles of quarter degree pixels, seasonal rain rate, and seasonal rain coverage

Decade-long radar and rain gauge datasets from multiple ground validation sites have allowed detailed analyses of diurnal rainfall cycles, seasonal rain rates, and seasonal areal rainfall coverage patterns from various climatological regimes. Site-specific diurnal rainfall analysis provide observations of local rainfall patterns, daily rainfall maximum and minimum cycles, and terrain-influenced rates and coverage; all of which benefit climatological, precipitation modeling and forecasting, algorithm development, and data assimilation studies. Several recent diurnal rainfall studies have focused on the large scale diurnal cycle, as estimated by satellite such as the Tropical Rainfall Measuring Mission (TRMM); however, our approach is focused over smaller areas (0.25º x 0.25º), with near round-the-clock sampling via ground-based radars and rain gauges. We observed the decade-long (2000-2009) diurnal cycle of rainfall over quarter degree pixels using quality controlled gauge and radar data from the TRMM Ground Validation (GV) radar sites: Melbourne, Florida; Houston, Texas; Darwin, Australia; and Kwajalein, Republic of the Marshall Islands. A seasonal analysis of these pixels was also studied. Additional seasonal analysis of the diurnal cycle of conditional mean rain rate and the percentage of areal coverage for five different precipitation intensity thresholds (0, 1, 2, 5, and 10 mm hr^-1) was performed.

Analysis of Melbourne reveals the time of maxium rainfall is earliest near the coast and the percentage of areal coverage during Winter has a bimodal cycle. Analyzing Houston we find the time of maxium rainfall to be earlier to the southeast and mean rainfall to be highest to the south. Percentage of areal coverage during the Fall at Houston reveals a morning maximum, which we suggest is due to the influence of nocturnal mesoscale convective systems generated over the hill country. Analysis of Darwin shows maxium, minium, and mean rainfall to be higher along the coast and percentage of areal coverage during the wet season has three modes. Analyzing Kwajalein we find maximum and minium rainfall are slightly higher to the north and percentage of areal coverage during Sep-Oct-Nov reveal a large nocturnal maximum. The meteorological factors that cause these observations will be discussed.

The availablity of high resolution high quality radar and gauge data has given us the ability to analyze the diurnal cycle of rainfall on a small scale and seasonally. Our observations provide crucial data for instantaneous and climatological validation of satellite retrievals and will prove essential to the improvement of physically-based satellite retrievals.