Classification of Synoptic Patterns With Mesoscale Mechanisms for Downslope Windstorms in Korea Using a Self-Organizing Map

Downslope windstorms (DWs) are responsible for wildfires, wind gusts, and turbulence on the lee side of the Taebaek Mountains in the Yeongdong (YD) region of Korea. We classified the synoptic conditions of the windstorms in the YD region using a self-organizing map (SOM). For windstorm events from 1979 to 2019, sea level pressure anomalies were used to train the SOM. It was found that the synoptic patterns could be classified into three representative types: (1) the south-high and north-low pattern in the spring, (2) the west-high and east-low pattern in the winter, and (3) the strong low-pressure system passing through the northern part of Korea. At 850 hPa, prevailing southwesterly and northwesterly flows with warm and cold advections were dominant in Types 1 and 2, respectively. And, Type 3 presented a well-developed baroclinic system of cyclone. Adiabatic warming by downslope windstorm was the strongest in Type 1, which was likely to have a huge impact on the spread of wildfires. Three mesoscale generation mechanisms were examined under different synoptic patterns. The hydraulic-jump theory was dominant for the windstorms in Type 2 due to upstream flows with moderate Froude numbers and inversion layers. The partial reflection of mountain waves was found in all types but was more frequent in Type 1 than others. DWs with wave breakings at critical levels mostly occurred in Type 1. This objective classification of weather patterns responsible for DWs in the YD region may improve predictions and future projections of this event, particularly in light of ongoing climate changes.