Satellite and Ground-Based Precipitation Retrievals during Hurricane Landfalls

The on-going 2018 hurricane season yielded land-falling hurricanes Florence and Michael, both of which produced major impacts on coastal populations, properties and landscapes in the Southeastern U.S. These hurricanes represent the latest in a sequence of recent impactful hurricanes that include Harvey, Irma and Arthur. Recent advances in observations of Florence and previous land-falling hurricanes from ground-based NEXRAD dual-polarimetric radars, spaceborne dual-frequency radar and passive microwave sensors from the Global Precipitation Measurement mission provide insights into their microphysical characteristics and precipitation properties. This study compares surface precipitation accumulation from ground- and space-based observations over multiple scales in the context of the 3D structure of hurricane microphysics to interpret differences between the precipitation products.

Accurate characterization of discrepancies among these estimates is critical. The GPM Level III (IMERG) precipitation estimates are compared to independent, high quality and high-resolution NEXRAD-based precipitation estimates derived from the Multi-Radar/Multi-Sensor (MRMS) product. MRMS provides a consistent research framework for direct cross-comparison of satellite- and ground-based precipitation retrievals during hurricane events. Infrared and passive microwave components of IMERG precipitation are separately investigated and contrasted. Preliminary study suggests a strong disparity in the sign of the relative bias between microwave and IR-based estimates in the hurricanes examined.

Sources of satellite-ground disagreement are investigated with a focus on warm rain processes (i.e., droplet collision/coalescence) that enhance rain rates and have traditionally represented a challenge for the interpretation of radar observations (i.e., large numbers of small drops) and satellite observations (i.e., limited ice content) in estimating precipitation. It is hypothesized that the vertical structure of hurricanes, specifically how the ice water content relates to the liquid water content along with warm microphysics processes, are key for improved quantitative precipitation estimation in hurricanes from space- and ground-based sensors.