Testing the Attenuation-based QPE Methodology Using Polarimetrically Upgraded WSR-88D Radars

In spring 2013 all 122 NWS WSR-88D radars have been upgraded by adding dual-polarization capability. The improvement of quantitative precipitation estimation (QPE) with dual-polarization measurements is one of the primary goals of the upgrade. In addition to radar reflectivity, differential reflectivity, and specific differential phase, the specific attenuation A emerges as a promising variable for a more accurate QPE. The specific attenuation can be reliably estimated by a polarimetric radar from the combinations of the measurements of radar reflectivity and total differential phase. The advantages of the R(A) estimator of rain rate R include its low sensitivity to DSD variability and immunity to partial beam blockage, radar miscalibration, and impact of wet radome. Dual-polarimetric observations by several upgraded WSR-88D radars are utilized to examine the performance of R(A). The results of observations confirm all mentioned benefits of the R(A) technique. To validate the accuracy of R(A) estimate under different atmospheric conditions, the R(A) rainfall accumulations have been obtained for the events with different precipitation types and compared with rain gauge measurements. The results are promising, especially in the areas affected by partial blockage of the radar beam.

The R(A) methodology also provides a solution for efficient compositing / mosaicking rainfall accumulation products because it eliminates the errors caused by reflectivity mismatch between neighboring radars which is still quite common on an operational radar network. Several mosaic rainfall accumulation maps estimated using R(Z) and R(A) from adjacent WSR-88D radars have been obtained. The R(A) rain totals estimated from the two radars show seamless mosaics because specific attenuation is immune to radar miscalibration. In contrast to R(A), the discontinuity in rain total retrieved from the R(Z) relation is often observed along the equidistance line between neighboring radars.