Local Gauge Correction of Radar QPE in the Multi-Radar Multi-Sensor System

Weather radar has been providing operational quantitative precipitation estimation (QPE) for over a decade. The radar-based QPE has advantages over in situ gauge observations in that the former provides continuous spatial coverage of precipitation systems with a higher spatio-temporal resolution. However, radar QPE is subject to uncertainties due to radar calibration errors, vertical variations of precipitation between the radar observation height and the ground, uncertainties in empirical relationships converting radar observations into precipitation rates, etc. A local gauge correction (LGC) of radar QPE is a common practice for reducing the radar QPE uncertainties. The LGC in the Multi-Radar Multi-Sensor (MRMS) system applies a correction to hourly radar QPEs by spatially interpolating radar-gauge differences onto the radar QPE grid and then subtract the interpolated difference field from the radar QPE. An inverse distance weighting (IDW) function was adopted for the interpolation and the power parameter and the cutoff radius in the IDW was calculated every hour via a cross-validation that minimizes the interpolation error of radar-gauge differences at all gauges. The LGC provides consistent improvements over the radar QPE when compared to independent gauges although the extent of the improvements depends on the precipitation and gauge distributions. This paper presents several case studies of the MRMS LGC QPE with different precipitation regimes and gauge densities.