Polarimetric and MRMS Observations of Hailstorms using an All-Digital, S-Band, Phased Array Radar

Rapid-scan polarimetric radar data of hailstorms have shown operational utility as these observations may provide a better understanding of the processes that drive hail growth and descent. Radar-derived algorithms, such as those used in the Multi-Radar Multi-Sensor (MRMS) system, blend neighboring radars together into a seamless product that provides warning decision makers with estimates of hail properties at both the surface and aloft. Despite the benefits that polarimetric data provide, the current WSR-88D network produces volumetric updates every ~5 – 7 min, which can slow the detection of hail aloft. In contrast, phased array radars (PARs) provide vertically-dense, volumetric updates on the order of tens of seconds. This is because PARs can use imaging, in which the radar transmits an intentionally broadened beam and creates multiple, simultaneous, narrow beams within the transmitted mainlobe. Scanning modes like imaging may allow for an improved detection and characterization of polarimetric signatures related to hail as the full depth of a storm can be sampled nearly simultaneously. However, only a few dual-polarization PAR-based datasets of hailstorms currently exist.

Horus is an all-digital S-band polarimetric PAR developed at the Advanced Radar Research Center funded by the NOAA’s National Severe Storms Laboratory (NSSL). Horus data were collected during the spring 2024 convective season across central Oklahoma using advanced digital beamforming modes, spanning from 5 km in range to upwards of 100 km from Horus. Two different imaging modes were applied: 1D spoiling in elevation with mechanical rotation in azimuth (with imaging beams generated in the vertical plane) and 2D spoiling (with imaging beams generated in the horizontal and vertical planes) with the radar electronically scanning in stationary mode. As a result of these scanning techniques, volumetric data, scanning up to 30° in elevation, were collected with update intervals of 30 s or less.

Polarimetric data collected by Horus have been compared to nearby WSR-88D data, as well as WSR-88D data at similar standoff ranges to Horus, to evaluate differences and similarities in the polarimetric signatures. Data were ingested into the Warning Decision Support System - Integrated Information (WDSS-II) software (a core component of MRMS) to evaluate how the rapid temporal resolution data and PAR scanning techniques impact hail related MRMS single radar products, including echo tops, the maximum estimated size of hail (MESH), and the operational hydrometeor classification algorithm (HCA). The higher spatial and temporal resolution of Horus has allowed for radar signatures, such as the BWER, to be better resolved (in time) compared to present WSR-88D data. This presentation will discuss the benefits of rapid-scan vertically-dense observations of hail and their impacts on operational products such as MESH.