C-Band Polarimetric Radar QPE Based on Specific Differential Propagation Phase for Extreme Typhoon Rainfall

Abstract

To obtain accurate radar quantitative precipitation estimation (QPE) for extreme rainfall events such as land-falling typhoon systems in complex terrain, a new method was developed for C-band polarimetric radars. The new methodology includes a correction method based on vertical profiles of the specific differential propagation phase (VPSDP) for low-level blockage and an optimal relation between rainfall rate (R) and the specific differential phase (K DP ). In the VPSDP-based correction approach, a screening process is applied to K DP fields, where missing or unreliable K DP data from lower tilts caused by severe beam blockage are replaced with K DP data from upper and unblocked tilts. The K DP data from upper tilts are adjusted to account for variations in the vertical profile of K DP . The corrected K DP field is then used for rain-rate estimations. To acquire an accurate QPE result, a new R(K DP ) relation for C-band polarimetric radars was derived through simulations using drop size distribution (DSD) and drop shape relation (DSR) observations from typhoon systems in Taiwan. The VPSDP-based correction method with the new R(K DP ) relation was evaluated using the typhoon cases of Morakot (2009) and Fanapi (2010).

Operational C-Band Dual-Polarization Radar QPE for the Subtropical Complex Terrain of Taiwan

“…The ( DP ) relation is also able to provide more accurate QPE than other estimators during heavy rain events [9]. However, DP data may become unavailable when the radar beam is severely or entirely blocked [8]. Higher tilt DP data needs to be used in the rainfall rate estimation under this situation, and a correction for the vertical variation is necessary to achieve accurate estimations.…”

“…Higher tilt DP data needs to be used in the rainfall rate estimation under this situation, and a correction for the vertical variation is necessary to achieve accurate estimations. Wang et al [8] proposed a VPSDP-based correction approach in which a predefined mean VPSDP was determined from 24-hour data and then used to adjust high altitudes DP to the ground level (or the radar level, whichever is higher).…”

“…With the dual-polarization measurements, a variety of polarimetric QPE algorithms have been developed in the last decade. The relations utilizing different combinations of , DR , and DP were obtained using either simulated or measured drop size distribution (DSD) and drop shape relations (DSR) (e.g., [4,[6][7][8]). Comparing to conventional -approaches, the polarimetric rainfall estimation algorithms were shown to deliver enhanced rainfall estimation because of polarimetric variables' ability of improving the radar data quality, distinguishing rain echoes from other echoes (snow, hail, and clutter), and reducing the impact of DSD variability [9].…”

“…Projecting reflectivities from higher tilts to the ground level through vertical profile of reflectivity (VPR) correction is one of the methods that can mitigate QPE errors due to orographic effects (e.g., [10,11,21]). Although some studies (e.g., [12,13]) had indicated that the specific differential phase DP was immune to attenuation and miscalibration, severe beam blockages still cause missing or unreliable DP [8], and higher tilt DP data should be corrected for nonuniform vertical profile of specific differential phase (VPSDP) before being used in the rainfall estimation. Wang et al [8] showed that the -DP with VPSDP-based correction produced significantly improved rainfall estimation in mountain regions over the conventional -relation.…”

Radar Vertical Profile of Reflectivity Correction with TRMM Observations Using a Neural Network Approach

“…Morakot landed on Taiwan at midnight (local time) on 8 August and brought a maximum accumulated precipitation of 2600 mm during 4 days (Wang et al 2013). Morakot landed on Taiwan at midnight (local time) on 8 August and brought a maximum accumulated precipitation of 2600 mm during 4 days (Wang et al 2013).…”