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

A 16-yr record of hail reports over the southeast U.S. and from weather stations in China are collocated with Precipitation Features (PF) derived from the Tropical Rainfall Measuring Mission (TRMM) radar and passive microwave observations. While U.S. hail reports are dominated by cases with hail size greater than 19 mm, hail reports in China mostly include diameters of 1-10 mm and mostly occur over the Tibetan Plateau. The fraction of PFs collocated with hail reports (hail PFs) reaches 3% in the plains of the U.S. In China, the fraction is higher in high elevation regions than low elevation regions. Hail PFs in the U.S. show lower brightness temperatures, higher lightning flash rates, stronger maximum reflectivity, and higher echo tops than those in China, consistent with the larger hail diameters in the U.S. reports. The average near surface maximum reflectivity of hail PFs at high elevations (≥ 2000 m) in China is about 5 dB smaller than those at low elevations. Larger hail is reported with PFs having stronger maximum reflectivity above 6 km, though the median of maximum reflectivity values at levels below 5 km is close among the storms with large and small hail sizes. Using collocated hail reports in US, hail detection methods with radar reflectivity and microwave brightness temperature are developed. Threshold of 44 dBZ at -22^oC is found to be with the highest CSI and HSS scores to detect hail with size > 19 mm. After applying these methods globally, the detection differences between radar and passive microwave methods are found over the Amazon, western Pacific and Indonesian region, and also Central Africa. How these differences are probably related to the properties of intense convection is discussed.