Multiplatform Comparisons of Rain Intensity for Extreme Precipitation Events

Abstract

Rainfall intensities during heavy rain events over the continental U.S. are compared for several advanced radar products. These products include the following: 1) Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) near-surface estimates; 2) NOAA Quantitative Precipitation Estimation very high resolution (1 km, instantaneous) radar-only national mosaics (Q2); 3) very high resolution gauge-adjusted radar national mosaics, which we have developed by applying a gauge correction on the Q2 products; and 4) several independent C-band dual-polarimetric radar-estimated rainfall samples collected with the Advanced C-band Radar for Meteorological and Operational Research (ARMOR) radar in Alabama. These instantaneous rainfall rate fields [i.e., 1)-3)] can be considered as radar products with the largest coverage currently available from space- and ground-based radar observations. Although accumulated rainfall amounts are often similar, we find the PR and Q2 rain-rate histograms quite different. PR rain-rate histograms are shifted toward lower rain rates, implying a much larger stratiform/convective rain ratio than do products such as Q2. The shift is more evident during strong continental convective storms and not as pronounced in tropical rain. A “continental/maritime regime” behavior is also observed upon adjusting the Q2 products to rain gauges, yet the rain amount more closely agrees with that of PR. The independent PR/ARMOR comparisons confirm this systematic regime behavior. In addition, comparisons are performed over central Florida where PR, Q2, and the NASA TRMM ground validation products are available. These comparisons show large discrepancies among all three products. Resolving the large discrepancies between the products presents an important set of challenges related to improving remote-sensing estimates of precipitation in general and during extreme events in particular.