Observational analysis of an exceptionally intense hailstorm over the Mediterranean area: Role of the GPM Core Observatory

- Synergy of GEO VIS-IR, LEO PMW, ground and space-borne radar, lightning network.
- GPM-CO reveals unique features of massive hailstorm in Central Mediterranean.
- Record low TBs and DPR Ku 40 dBZ and 20 dBZ echo top heights at 14 km and 16 km.
- Updraft strength related to IC and CG stroke evolution, polarity, and distribution.
- IR cloud top cooling rate of 4.5 K min− 1 (up to 198 K), 21,000 strokes in 2 h.

On 5 September 2015 a violent hailstorm hit the Gulf and the city of Naples in Italy. The storm originated over the Tyrrhenian Sea dropping 7-10 cm diameter hailstones along its path. During its mature phase, at 08:47 UTC, the hailstorm was captured by one overpass of the Global Precipitation Measurement mission Core Observatory (GPM-CO) embarking the GPM Microwave Imager (GMI) and the Ka/Ku-band Dual-frequency Precipitation Radar (DPR). In this paper, observations by both GMI and DPR are thoroughly analyzed in conjunction with other spaceborne and ground-based measurements, to show how the GPM-CO integrates established observational tools in monitoring, understanding, and characterizing severe weather. Rapid-scan MSG SEVIRI images show an extremely rapid development, with 10.8 μm cloud-top temperatures dropping by 65 K in 40 min down to 198 K. The LIghtning NETwork registered over 37,000 strokes in 5 h, with intracloud positive stroke fraction increasing during the regeneration phases, when ground-based polarimetric radar and DPR support the presence of large graupel/hail particles. DPR Ku 40 dBZ and 20 dBZ echo top heights at 14 km and 16 km, respectively, indicate strong updraft and deep overshooting. GMI extremely low brightness temperatures (TBs) in correspondence of the convective core (158, 97, 67, and 87 K at 18.7, 36.5, 89 and 166 GHz) are compatible with the presence of massive ice particles. In two years of GPM global observations the storm ranks as fourth and first in terms of minimum 36.5 and 18.7 GHz (V-pol) TBs, respectively. This study illustrates GPM-CO sensing capabilities for characterizing the structure of such severe hailstorm, while providing observational evidence of its intensity and rarity, both globally and over the Mediterranean area.

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