Space-time variation of large hail-producing mesoscale convective systems over a complex terrain of the Indian subcontinent as revealed by the integrated Tropical Rainfall Measuring Mission and Global Precipitation Measurement observations

Space-time variation of large hail-producing mesoscale convective systems (MCSs) is investigated over the eastern and northeastern parts of the Indian subcontinent during the premonsoon (March-April-May) season by using long-term (1998-2020) integrated observations of Precipitation Radar and Microwave Imager onboard the Tropical Rainfall Measuring Mission (TRMM) and Global Precipitation Measurement (GPM) satellites. A threshold of 37.0-GHz polarization-corrected temperature (<= 176 K) is utilized as a hail proxy. Qualitatively, the space-time variation of satellite-detected hailstorms is reasonably in good agreement with the available hail reports at the ground. The large hail-producing MCSs are most frequently observed over the plains, whereas such MCSs are not found over mountains. The MCSs in April have the highest probability to contain hail though the hail-producing MCSs are more common in May. The average morphological and microphysical properties are distinctly different for the MCSs with and without hail. Compared to the active convective cores of MCSs without hail, the hail-producing convective cores of MCSs (a) are extended higher vertically and wider horizontally, (b) are associated with much larger area (similar to 1,000 vs. 100 km(2)) occupied by radar reflectivity larger than 40 dBZ in the mixed-phase region, and (c) are associated with larger values of cloud ice water content (CIWC; 395 vs. 153 mg center dot m(-3)) in the mixed-phase region. The results from the high-resolution ERA5 reanalysis data show that the hail-producing MCSs are more sensitive to synoptic forcing than the MCSs without hail. Very strong mean sea-level pressure anomalies over the whole northern part of India along the Himalayan foothills to the Bay of Bengal occur for the MCSs with hail days. The findings of this study will help the forecasting of these hailstorms and mitigation of their damage within this less explored region.

Automated summary

The space-time variation of large hail-producing mesoscale convective systems (MCSs) over the eastern and northeastern parts of the Indian subcontinent during the premonsoon season was investigated using long-term satellite observations. The results showed that the occurrence of hailstorms was consistent with ground-based reports and was most frequent over plains rather than mountains. The study also found distinct differences in the morphological and microphysical properties between MCSs with and without hail, with hail-producing systems exhibiting higher vertical and horizontal extents, larger radar reflectivity areas in the mixed-phase region, and higher cloud ice water content.