Abstract
Precipitation statistics from Global Precipitation Measurement Core Observatory Dual-frequency Precipitation Radar (GPM DPR) are underestimated due to systematic bias depending on the scanning angle. Over five years of GPM DPR KuPR Version 06A data, the precipitation anomaly is −7% and −2% over land and ocean, respectively. This study improves the estimation of low-level precipitation-rate profiles and the detection of shallow storms (with top heights of ≤2.5 km), using reference datasets of near-nadir measurements.
First, the low-level precipitation profile (LPP) is updated using an a priori near-nadir database generated from structural-characteristics related variables of the precipitation and environmental parameters. The LPP correction increases precipitation over areas where downward-increasing precipitation profiles are dominant below 2 km, such as at high elevations and at middle and high latitudes. Globally, the LPP correction increases precipitation by 5%. Second, the effect on precipitation data of missing shallow storms is estimated using the angle-bin difference in the detectability of storms with a top height of ≤2.5 km. The effect of the shallow-precipitation deficiency (SPD) is comparable in magnitude to that of the LPP correction. A priori lookup tables for the SPD correction, constrained by the clutter-free bottom level and spatially averaged shallow-precipitation fractions, are constructed so that the correction applies to gridded statistics at 0.1° and three-month scales. The SPD correction enhances precipitation by 50% over specific low-rainfall oceans in the sub-tropics and at high latitudes, where shallow precipitation dominates. Based on these two corrections, precipitation increases by 8% and 11% over land and ocean, respectively. At latitudes between 60° N and 60° S, the difference in KuPR compared with satellite-gauge blended products is reduced from −17% to −9%, whereas with gauge-based products is reduced from −19% to −15% over land.
