Hailstorm Events Over A Maritime Tropical Region: Storm Environments, Characteristics, and Possible Mechanism
In recent years, the Maritime Tropics (mT) have experienced an increase in hail events, including five occurrences over Surabaya, Indonesia. Previous studies of mT hailstorms have been limited to individual case studies. A more comprehensive investigation is needed to enhance understanding of hailstorms in this region and may also offer broader insights into hailstorm development worldwide. In the first part of this study, we evaluated the pre-storm environments using the Weather Research and Forecasting (WRF) Model. Five hailstorm cases were selected, along with five additional storms, to help differentiate between storms producing hail and those lacking hailfall. Compared to other hail-prone regions, mT environments exhibit moderate CAPE, significantly less deep-layer shear, and much higher low-level specific humidity. These environmental characteristics typically support ordinary single-cell, pulse-type storms. A new variable introduced in this study, NetCAPE—defined as the net CAPE after accounting for precipitation loading and any CIN at lower levels—shows promise in distinguishing hail from no-hail events in the mT. The median NetCAPE for the five hail events is over 40% greater within various layers of the hail growth zone. When combined with lower near-surface relative humidity and melting level heights, NetCAPE effectively separates most hail cases from no-hail ones. In the second part of this study, we employed idealized simulations of one of the observed mT hailstorms using Cloud Model 1 (CM1) to examine further how NetCAPE supports the growth of raindrops into hail embryos and their transport into the hail growth zone (HGZ). Preliminary results of these simulations will be presented, as well as a discussion of future work.