| Description |
Tropical Measuring Mission (TRMM) precipitation radar (PR) 2A25 V7 retrievals show that precipitation features (PFs) with the tallest maximum 40 dBZ echo heights are rarely the same PFs that exhibit the most extreme near-surface rainfall rates. To investigate the impacts of potential weaknesses in the 2A25 V7 retrievals, due to potential attenuation of the Ku-band signal, 14 years of June-August retrievals are compared to June-August 2014 hourly Weather Surveillance Radar - 1988 Doppler (WSR-88D) dual-polarimetric S-band data for 28 radars over the southeastern United States (SEUS). For more direct comparison, TRMM Ku-band measurements are converted to S-band approximations. Rain rates for WSR-88D data are approximated using the CSU-HIDRO algorithm, which calculates rain rates from reflectivity (Z), differential reflectivity (ZDR), and specific differential phase (KDP) relationships. This research aims to not only investigate the difference between TRMM PR and WSR-88D retrievals of reflectivity and rain rate, but also to investigate how apparent differences relate to TRMM path integrated attenuation (PIA), and WSR-88D KDP, ZDR and calculated hail fraction. Tropics-wide TRMM retrievals confirm previous findings of a low overlap of extreme convective intensity and extreme near-surface rain rates. WSR-88D data also confirm that this overlap is low, but show that it is likely higher than TRMM PR retrievals indicate, approximately 30% higher in the SEUS for the 99th percentiles of maximum 40 dBZ heights and low-level rain rates. For maximum 40 dBZ echo heights that extend into regions likely containing ice, mean WSR-88D reflectivities are approximately 2 dBZ higher than TRMM PR reflectivities. Higher WSR-88D-retrieved rain rates for a given low-level reflectivity combine with these higher low-level reflectivities to produce much greater mean WSR-88D rainfall rates than TRMM PR as a function of maximum 40 dBZ height, for heights that extend into regions likely to have ice. Investigations of TRMM PR PIA, and WSR-88D KDP, ZDR, and hail fraction indicate that the TRMM PR 2A25 V7 algorithm is possibly misidentifying low-mid level hail or graupel as greater attenuating liquid, or vice versa. This possible misidentification results in 2A25 V7 Z-R relationships that likely produce low biased rain rates in intense convection. |
