EnvironmentAsia (Jan 2015)
Characteristics of Hailstorm over Northern Thailand during Summer Season
Abstract
This study focused on the potential parameters, as a result of the upper-air sounding with radiosonde and of the dual polarization radar for detecting hailstorms. The data were collected during the 2012 summer consisting of 12 hail and 1129 no-hail rainstorms of seven studied dates from April to May, 2012. They were analyzed to discern the character of hail and use them as data for detecting hail echoes and for severe weather forecast in upper Thailand. On the day of hail, the instability indices were high enough to contribute to its formation. The following indices include Lifted Index (LI), Showalter Index (SI) and Convective Available Potential Energy (CAPE). LI and SI displayed the marginally instability ranged -1 to -4. In the case of CAPE, it could reach the extreme instability (CAPE > 2500 J/kg) and also came with the large updraft speed. TITAN software (Thunderstorm Identification, Tracking, Analysis and Nowcasting) was also applied for comparing rainstorms with hailstorms. The significant seven echo characteristics included storm period, speed, mean-maximum reflectivity in the horizontal polarization (ZH), area, volume and mass. Based on the character and frequency distributions in summer, hailstorms had greater values of storm duration, area, volume, mass, speed and highest reflectivity than individual rainstorms. Besides, the mean reflectivity of the storms was a negligible factor to identify the type of storm.For the case study on hail by determining polarimetric radar measurement at S-band across Chiang Maun, Northern Thailand, radar signatures with EDGE software showed that the hail was detected 100% during its falling. It also presented as followings: Vertically integrated liquid (VIL) exceeding 100 kg/m2, ZH over 60dBZ near the surface and ETOP greater than 17 km. Differential reflectivity (ZDR) of rain-hail mixtures almost reached zero. In addition, the coincidental values of correlation coefficient (CC) were ranged 0.988 and 0.996, and specific differential phase (KDP) was ranged 2.1 and 3.2 deg/km.
