On the Relationship between Large Hail and Polarimetric Signatures at C-Band: a Case Study in Sierras de Córdoba, Argentina

During the austral warm season, central part of Argentina is affected by deep moist convection producing high impact weather events. Severe damage in infrastructure and agriculture can be observed associated to severe weather (large hail, strong damage wind gust, tornadoes, flash flood, and lightning).

Dual-polarized weather radars have the capability to detect and identify different categories of hydrometeors in liquid, mixed, and ice phases present in convective storms. In particular, hydrometeor classification helps to detect hail shafts within storms, but this poses a special challenge due to polarimetric characteristics of hailstones depending on their size, shape, falling behavior, and are strongly affected by the degree of melting and the probing radar wavelength. In addition, strong attenuation and differential attenuation in hail at C-band further complicates the issue of hail detection and sizing.

On the afternoon of December 7th, 2015, a severe hail storm (maximum 50 mm diameter) developed close to Sierras de Córdoba near Alta Gracia (31°40'S, 64°26'W) in Central Argentina. Flash floods and damaging winds were associated with this local severe storm. The aim of this paper is to explore the application of a hydrometeor identification (HID) scheme based on a fuzzy-logic approach in this case study observed by C-band dual-polarization Doppler weather radar located in the nearby city of Córdoba. Six hydrometeor classes have been established and named as follows: BD (big drops), R (rain), H (hail), G (graupel/small hail), S (snow), and IC (ice crystals). While in previous work in the region, HID scheme was focused on correlation coefficient, differential reflectivity and horizontal reflectivity variables, in the present paper specific differential phase and environmental temperature information are incorporated showing the importance of this variable. The impact of severe attenuation and differential attenuation will be discussed at C-Band, in the perspective of operational applications (e.g., nowcasting, flight safety, among others). Also an analysis of lightning activity from two different lightning datasets (The University of Washington WWLLN and Vaisala GLD360) along the duration of the hail storm was analyzed applying a jump algorithm in order to relate the occurrence of hail and other severe weather phenomena and polarimetric radar observables in this case.