Evaluation of detecting algorithm for potential refreezing rain area using the road icing accidents report

Freezing rain is a meteorological phenomenon in which precipitation melts in the upper atmosphere, transforming into super-cooled droplets near the ground due to lower temperatures. In Northern Europe and North America, strong winter storms often accompany freezing rain, leading to road or facility damage. In Korea, several traffic accident have also occurred due to road icing caused by freezing rain, demanding the development of monitoring technologies for enhanced safety measures. In order to provide the information about the road hazard warning and ensuring safety, we analyzed the atmospheric condition and dual-polarimetric characteristics for road icing and developed the algorithm to detect the potential refreezing rain area by using dual polarization radar and 3-D wet-bulb temperature.
 We selected road icing accidents including precipitation and inversion layer events from 2019 to 2021, and analyzed the changes in surface temperatures and wet-bulb temperatures at surface and the hydrometeor classified using dual-polarization variables at upper layer. The hydrometeor at the accident sites were classified with rain or super-cooled droplet, and wet-bulb temperatures ranged between -2 to 1.5 degrees. This information was used to determine the potential refreezing rain area. The inversion layer was also analyzed by the calculation of 3-dimensional wet-bulb temperatures through multi-quadratic interpolation using various observations (AWS, sounding, Buoy, etc.) and the Korea Local Analysis and Prediction System (KLAPS). The dual-polarization variables were employed to classify the hydrometeor type and investigate the possibility of ice particle melting within the inversion layer. The area for potential refreezing rain was designated as dangerous/cautious zones based on ground temperature conditions when snow particles melted within the inversion layer.
The performance of the algorithm for potential refreezing rain areas was evaluated during cold seasons when incidents of refreezing rain, often referred to as black-ice events occurred. We analyzed the hourly and monthly frequencies of detecting dangerous/cautious zones during traffic accidents caused by refreezing rain.

※ This research was supported by the "Development of radar based severe weather monitoring technology (KMA2021-03121)" of "Development of integrated application technology for Korea weather radar" project funded by the Weather Radar Center, Korea Meteorological Administration.