MRMS Dual-Polarization Radar Synthetic QPE

The dual-polarization (DP) upgrade of the US NEXRAD network was completed in 2013. As a result, a near surface hydrometeor classification and a DP radar quantitative precipitation estimation (QPE) were implemented at each radar site. The hydrometeor classification provided a much improved identification of non-hydrometeor echoes over the single-polarization (SP) radar techniques, and the DP QPE had much less contamination from anomalous propagation clutter and biological scatterers. The DP QPE, based on reflectivity (Z), differential reflectivity (Zdr) and specific differential phase (Kdp), provided improved precipitation estimates over the previous SP QPE in some warm season events where the freezing level was high. However, it had relatively large random errors due to its sensitivity to errors in Zdr, which can be significant at times. The DP QPE also suffered from discontinuities and some biases near the melting layer. Based on these initial assessments, an alternative DP radar synthetic QPE was developed within the Multi-Radar Multi-Sensor (MRMS) system.

The MRMS DP QPE calculates precipitation rates (R) based on a combination of specific attenuation (A), Kdp, and Z. Specific attenuation has advantages of being immune to calibration errors in Z and Zdr and more linearly related to the liquid water amount in the radar beam path than other radar variables. However, A is not applicable in areas containing ice. Therefore, the MRMS DP QPE applies R(A) relationship in areas where radar is observing pure rain, R(Kdp) in regions containing hail and a vertical profile corrected R(Z) elsewhere. The vertical profile correction is to account for reflectivity variations in and above the melting layer.

The MRMS DP QPE has been tested in real-time over CONUS since April 2017. Initial test results will be presented at the conference.