This page presents rainfall results from radar and rain gauge data collected during TRMM LBA. The work is collaboration between Tom Rickenbach (NASA Mesoscale Processes Branch), Brad Fisher (NASA TRMM Office), and the CSU Radar Meteorology Group.
Diurnal Composite Comparison:
1. The onset of the 'noon balloon' - the time of day the afternoon convection explodes (1100-1200LT), is just the same comparing gage and TOGA radar. The S-pol plot shows the afternoon rainfall peaks about 1 hr later compared to the gauge composites. In the westerly, both gauge and S-pol have a bimodal shape in the afternoon, although the separation of the peaks is off by a few hours.
2. The gauge easterly diurnal composite has a nocturnal peak almost as large as the afternoon peak. The TOGA radar observations don't show anything like this (the TOGA composite shows a very weak nocturnal max independent of regime). The nocturnal max probably comes from a few nocturnal squall lines. Given the small areal sample of the gages, these nocturnal lines proabably dominate the gage diurnal composite (i.e., 15 February and 18 February in the easterly regime). S-pol shows a weak signal in the easterlies in the early am; however, it's much weaker than what the gauge plot indicates. S-Pol does not observe the gauge peak in the westerly regime around 07L.
3. The diurnal amplitude from the gauge westerly composite is somewhat smaller than for the gauge easterly composite. The same thing is also observed from the TOGA and S-pol composites (i.e. stronger diurnal amplitude in the easterly composite).
4. The rain gauge composites show alot more variation throughout the day in the stratiform rain estimate compared to the radar. This is probably due to the relatively small rain gauge data sample which produces larger random variability compared to the radars.
Radar Time Series:
Independent estimates came up with similar numbers for the percentage of time the radars sampled in each regime:
However, the time series were constructed using different techniques: conditional (TOGA) vs unconditional (S-pol) rain rate thresholds, 8-day (TOGA) vs 3-day (S-pol) filters. The main difference in the TOGA and S-pol time series of rain intensiity occurs in late January (S-pol does not show the increase that is observed in the TOGA data).