Testing a spaceborne passive-microwave severe hail retrieval over Argentina using ground-based dual-polarization radar data

Passive-microwave hail detection methods rely on the scattering signal produced by large ice hydrometeors. Recently, passive-microwave hail retrieval methods have been trained by pairing Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) and Global Precipitation Measurement (GPM) Microwave Imager (GMI) data with United States surface hail reports to present a global hail climatology. In particular, Southeastern South America (SESA) stands out as a hotspot for hail occurrence, more specifically northeastern Argentina. However, the analysis performed with the available ground hail reports in Argentina shows some differences from the available ground hail reports in Argentina, as it locates the most frequent hail storms in the southwestern (Mendoza and Cordoba) and northeastern (Misiones) regions of SESA. To assess the retrieval from a regional perspective, we take a case study approach and focus on polarization-corrected temperature features (PCTFs) with a detected P-hail>50%. We mainly rely on polarimetric weather radars and a hydrometeor identification algorithm (HID) as a proxy for ground truth. Results indicate that the hail retrieval responds mainly to low 37-GHz polarized corrected (brightness) temperatures (PCTs) and large PCTF area, while HID outputs show that high probabilities of hail also correspond to abundantly suspended graupel. The observed passive-microwave hail detection hotspot could be influenced by mesoscale convective systems with deep columns of graupel-sized frozen hydrometeors, common in northeastern Argentina.