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

Abstract

Passive-microwave hail detection methods rely on the scattering signal producedby large ice hydrometeors. Recently, passive-microwave hail retrievalmethods 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 reportsto present a global hail climatology. In particular, Southeastern South America(SESA) stands out as a hotspot for hail occurrence, more specifically northeasternArgentina. However, the analysis performed with the available groundhail reports in Argentina shows some differences from the available groundhail reports in Argentina, as it locates the most frequent hail storms in thesouthwestern (Mendoza and Córdoba) and northeastern (Misiones) regions ofSESA. To assess the retrieval from a regional perspective, we take a case studyapproach and focus on polarization-corrected temperature features (PCTFs)with a detected Phail > 50%. We mainly rely on polarimetric weather radarsand a hydrometeor identification algorithm (HID) as a proxy for ground truth.Results indicate that the hail retrieval responds mainly to low 37-GHz polarizedcorrected (brightness) temperatures (PCTs) and large PCTF area, whileHID outputs show that high probabilities of hail also correspond to abundantlysuspended graupel. The observed passive-microwave hail detection hotspotcould be influenced by mesoscale convective systems with deep columns ofgraupel-sized frozen hydrometeors, common in northeastern Argentina.