Critical Assessment of Microphysical Assumptions within TRMM Radiometer Rain Profile Algorithm Using Satellite, Aircraft, and Surface Datasets from KWAJEX

摘要

The Tropical Rainfall Measuring Mission (TRMM) Microwave Imagei precipitation profile letrieval algorithm (2al2) assumes cloud model-derived vertically distributed miciophysics as part of the radiative transfer-controlled inversion process to generaterain-rate estimates. Although this algorithm has been extensively evaluated, none of the evaluation approaches has explicitly examined the underlying micro-physical assumptions through a direct intercomparison of the assumed cloud-model microphysics with in situ, thiee-dimensional miciophysical observations. The main scientific objective of this study is to identify and overcome the foremost model-generated microphysical weaknesses in the TRMM 2al2 algorithm through analysis of (a) in situ aircraft miciophysical observations; (b) aircraft- and satellite-based passive microwave measurements; (c) ground-, aircraft-, and satellite-based radar measurements; (d) synthesized satellite brightness temperatures and radar reflectivities; (e) radiometer-only profile algorithm retrievals; and (f) radar-only profile or volume algorithm retrievals Results indicate the assumed 2al2 microphysics differs most from aircraft-observed microphysics where either ground 01 aircraft radar-derived rain rates exhibit the greatest differences with 2al2-ietrieved rain rates An emission-scattering coordinate system highlights the 2al2 algorithm's tendency to match high-emission/high-scattering observed profiles to high-emission/low-scattering database profiles. This is due to alack of mixed-phase-layer ice hydrometeor scatterers in the cloud model-generated profiles as compared with observed profiles. Direct comparisons between aircraft-measured and model-generated 2al2 microphysics suggest that, on average, the radiometer algorithm's microphysics database retrieves liquid and ice water contents that are approximately 1/3 the size of those observed at levels below 10 km Also, the 2al2 rain-tate retrievals are shown to be strongly influenced by the 2al2's convective fractionspecification A proposed modification of this factor would improve 2al2 rain-rate retrievals; however, fundamental changes to the cloud radiation model's ice parameterization are necessary to overcome the algorithm's tendency to produce mixed-phase-layer ice hydio-meteor deficits.