Analysis of Hail Characteristics and Detection of Hail Pre-Signal based on 3-dimensional Radar Data

Hail is generated within strong convective cells. In particular, hail from strong convective cells that develop rapidly can occur within 30 minutes. In that case, hail is difficult to be predicted and can cause a lot of damage in many part such as agriculture, aviation fields, and human life, etc. Pre-signal detection of developing hail will contribute to predicting hail and reducing damage. Therefore, Weather Radar Center of KMA (Korea Meteorological Administration) analyzed the characteristics of hail and developed an algorithm to detect hail pre-signal using the results of analysis.
In this study, 3-dimensional gridded radar reflectivity and temperature data were used to detect hail pre-signals. The results of pre-signal detection have 2 types of areas: “hail possible” and “hail warning”. The “hail possible” area represents the area where hail can develop before hail exists in the upper atmosphere. The “hail warning” area represents the area with a possibility of hail size of 2cm or larger. And the “hail warning” area is included in the “hail possible” area. For signal classification, 3-dimensional data based VIL (Vertically Integrated Liquid), UVIL (Upper-level VIL, -10~-40 degrees Celsius), 35 dBZ Echo top, freezing level height, and hail ground observation information such as hail size, observed time and location were used. Hail ground observation cases for 5 years were analyzed to determine thresholds for signal classification variables and verify this algorithm.
As a result of analyzing hail cases observed on 78 days, at 231 sites through this algorithm, all cases but 4 days were detected (ACC=0.81, POFD=0.22), and the hail signals were detected in advance of an average of about 40 minutes. And all 18 cases in which hail with a size of 2 cm or larger was observed were detected as “hail warning” signals. Comparing with the severe hail indices (SHI, POSH, MEHS) of previous studies, the “hail warning” areas in most of the cases were similar.

 

ACKNOWLEDGEMENTS
This research was supported by “Development of integrated radar analysis and customized radar technology (KMA2021-03021)” of “Development of integrated application technology for Korea weather radar” project funded by the Weather Radar Center, Korea Meteorological Administration.