Statistical agreement between observed microwave satellite radiances and NWP hydrometeors including hexagonal plates and rosettes

Accurate global observation of precipitation for all latitudes and seasons, and for all land, sea, and ice surfaces remains an elusive goal. One major obstacle to progress is lack of reliable global ground truth on horizontal and vertical scales consistent with those observed by satellite. For example, radar and scatter-dependent radiometric techniques respond to precipitation aloft, not on the ground, and can be unduly sensitive to large hydrometeors. On the other hand, rain gauges are excessively sensitive to local rainfall inhomogeneities and wind, and well-instrumented sites are rare. This paper quantitatively compares satellite observations with mesoscale numerical weather predictions of microwave brightness temperatures at those millimeter wavelengths most sensitive to hydrometeor structures and to the physics of precipitation. Only such models with high horizontal and vertical resolution allow comparisons of different sensors in detail. A Mesoscale Model, MM5, and a forward radiance program, TBSCAT, have been used to simulate radiances that would be observed from the Advanced Microwave Sounding Unit (AMSU-A and AMSU-B) aboard the NOAA-16 satellite for twenty-four globally representative storm systems, including ∼28,200 AMSU-A and 255,640 AMSU-B footprints, spanning a year. Good agreement has been obtained between histograms of coincident MM5-simulated and observed AMSU-A and AMSU-B radiances by adjusting ice parameter values in TBSCAT. Ice parameter values are consistent with the scattering for ice habits observed aloft, as computed using a Discrete Dipole Approximation program, DDSCAT6.1. These results suggest the potential use of MM5 as a rich new statistical form of ground-truth that will permit development of better precipitation estimators and improved understanding of precipitation itself, particularly in the more problematic areas of the globe.