A Numerical Study of Windstorms in the Lee of the Taebaek Mountains, South Korea: Characteristics and Generation Mechanisms

Abstract

The Yeongdong region, located east of the Taebaek Mountains, South Korea, often experiences severe windstorms in spring, causing a lot of damages, especially when forest fires spread out rapidly by strong winds. Here, the characteristics and generation mechanisms of the windstorms in the Yeongdong region on 8 April 2012 are examined through a high-resolution Weather Research and Forecasting (WRF) model simulation. In the Yangyang area, the steep descent of the isentropes on the lee slope of the mountain and their recovery farther leeward are seen. Inversion layers and incoming flow in hydraulic jump regime suggest that the hydraulic jump is responsible for the downslope windstorm. In the Jangjeon area, the plume-shaped wind pattern extending seaward from the gap exit is seen when the sea-level pressure difference between the gap inside and the gap exit, being responsible for the gap winds, is large. In the Uljin area, downslope windstorms pass over the region with weak wind, low Richardson number, and deep planetary boundary layer (PBL), making banded pattern in the wind and PBL height fields. This study demonstrates that the characteristics of the windstorms in the lee of the Taebaek Mountains and their generation mechanisms differ depending on local topographic features.

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

“…The occurrence of Type 1 (clusters 1, 2, and 5) was found to be dominant in the springtime when the moving synoptic high-and low-pressure systems were often observed. Consistently, previous studies (Jang & Chun, 2010;Kim & Chung, 2006;Lee et al, 2020) mentioned that this south-high and north-low pattern had often been observed when DWs occurred in the YD region in the springtime. Type 2 (clusters 3, 4, and 8) was found to mostly occur in the wintertime.…”

“…Accordingly, there were dense isobars across the Korean Peninsula between the high‐ and low‐pressure systems. This south‐high and north‐low pattern has often been mentioned in the previous studies as a typical synoptic SLP pattern that causes DWs in the YD region (Jang & Chun, 2010; Kim & Chung, 2006; Lee et al., 2020).…”

“…In addition, it may be possible to identify the dominant mesoscale processes under the specific large‐scale flow patterns related to DW events. Many previous studies (Jang & Chun, 2010; Kim & Chung, 2006; Lee et al., 2020) have shown that the generation mechanisms of hydraulic jump and critical‐level reflection were dominant in Type 1; however, more research is needed to fully understand dominant mesoscale (or local) mechanisms for DWs in Types 2 and 3. Nevertheless, this study indicated that the DWs in the YD region in Korea could be classified via objective synoptic SLP patterns using a machine‐learning algorithm (i.e., SOM).…”

“…In this study, SLP anomalies during 1979–2019 were used as input data to train the SOM. Though many studies have used several meteorological variables together (e.g., multivariate input data) for identifying weather patterns (Loikith et al., 2017; Nguyen‐Le & Yamada, 2019; Ohba et al., 2016), we only used SLP anomalies (e.g., univariate input data), which showed the representative synoptic‐scale patterns for DWs in the YD region, as revealed in previous studies (Cho et al., 2015; Jang & Chun, 2010; Kim & Chung, 2006; Lee et al., 2020). The classification results of multivariate input data (e.g., SLP and 850 hPa temperature anomalies) also showed similar patterns to the test with only SLP anomalies, so we used the classified SLP patterns from the SOM results with univariate input and then investigated the composite maps of the synoptic‐scale fields at 850 hPa, according to each cluster.…”

“…Many previous studies have reported that a south‐high and north‐low synoptic‐scale sea‐level pressure (SLP) pattern, accompanied by warm advection and an inversion layer near the top of the mountains, is often observed when DWs occur in the springtime in the YD region (Cho et al., 2015; Jang & Chun, 2010; Kim & Chung, 2006; Lee et al., 2020). Regarding the generation mechanisms of DW events in this region, Kim and Chung (2006) and Jang and Chun (2010) examined the hydraulic‐jump theory and wave breaking for a DW event on 5 April 2005 when a historical wildfire occurred.…”