Properties of Hail Storms over China and the United States from the Tropical Rainfall Measuring Mission

Spaceborne measurements can be used to apply uniform standards to severe storm detection across various regions.  But differences in the characteristics of ground-based measurements and storm reporting can complicate the interpretation of the space-borne measurements.  Satellite-based techniques that are "calibrated" using storms from a particular region may have questionable applicability to storms from a different region.  Here we compare Tropical Rainfall Measuring Mission (TRMM) satellite observations for two very different databases of hail storms.  The traditional Storm Data from the U.S. contains spotter-based reports, with hail mostly 19 mm (0.75") and larger.  A new compilation of hail reports at fixed weather observing stations in China lists hail diameters, mostly 1-10 mm.  Many of these hail reports from China would technically be considered graupel instead of hail, and very few would qualify as "severe thunderstorms" by the U.S. definition.  Weather stations across the Tibetan Plateau at elevations above 2 km contribute most of the reports in China.

The TRMM satellite signatures for these storms are consistent with the differences in hail diameter.  The storms producing larger hail in the U.S. have the strongest vertical profiles of radar reflectivity, the lowest microwave brightness temperatures, and the highest lightning flash rates.  From all these measures, the hail storms in China are weaker than those in the U.S. but stronger than ordinary precipitation systems that lack hail.  Besides the differences between the U.S. and China databases, stratifying the storms in the U.S. by hail size also leads to progressively stronger satellite signatures for storms producing larger hail.  There is considerable overlap in these satellite signatures for storms with hail of different sizes, partially due to the time lags between the hail reports and the associated TRMM overpasses.