Field-campaign Radar Data Collected in the Context of the Trmm Climatology: Comparisons of Observed Storm Morphology and Validation Opportunities

Many field campaigns using ground-based radars have been undertaken over the past four decades in the Tropics, and the data collected have been instrumental in improving our physical understanding of the global climate system. Unfortunately, the timescale of the radar observations collected in field campaigns (on the order of a month to several months) is less than the period of many modes of Tropical atmospheric variability that occur on longer timescales. Examples include seasonal variability, ENSO and the MJO, which most certainly influence the types, microphysics, and kinematics of rainfall systems in a given region, such that any climatology of the properties of rainfall systems derived from field campaign data may not be completely representative of the “true climatology” of rainfall systems in a given region. Routine radar observations are not widely available in the Tropics, so, until recently, one had to rely solely on field campaign data as our “ground truth” of the rainfall regimes present in the Tropics. With the launch of the Tropical Rainfall Measuring Mission (TRMM) satellite in December 1997, the precipitation radar (PR) has allowed the retrieval of snapshots of vertical reflectivity profiles it overflies. Thus, TRMM provides the opportunity to examine the climatology of rainfall systems on timescales longer than those seen by individual field campaigns. However, since TRMM only samples relatively infrequent snapshots of the radar reflectivity field in a given region, the ground-based radar remains the tool of choice for examining many characteristics of precipitating systems, including their life cycle and the local variability in rainfall in a given area, for example. The desire to intercompare radar data among field campaigns provides the motivation to use the satellite to understand the context of field-campaign-observed rainfall systems in the perspective of the satellite climatology, particularly in their rainfall and convective intensity and morphology characteristics, and where those storms fit into the statistical distribution of storms using such characteristics. The PR’s calibration is stable and accurate to within 1 dBZ (Iguchi et al. 2000), and Heymsfield et al. (2000) has shown that the PR is, in large part, a reliable standard to compare ground-based radar data with when the PR’s relatively low sensitivity and resolution are taken into account. 2. TRMM CLIMATOLOGY: THE PF DATABASE