Numerical Simulations of Three Downslope Windstorm Cases in Korea under the Different Synoptic-Scale Conditions

Downslope windstorms (DWs) have occurred frequently in the lee side of Taebaek Mountains in Korea. Using the Self-Organizing Map algorithm, Shin et al. (2022) suggested three representative synoptic-scale sea level pressure (SLP) patterns for DWs in this region. Type 1 shows south-high and north-low SLP pattern and occurs more frequently in spring with prevailing southwesterly across the mountains. Type 2 shows west-high and east-low SLP pattern dominantly in winter with prevailing northwesterly and cold advection in lower troposphere. Type 3 shows well-developed baroclinic cyclones passing in the northern side of the Korean peninsula. This study extends a previous study of Shin et al. (2022) by investigating three representative DW cases under the different synoptic-scale patterns using the Weather Research and Forecasting (WRF) model with the finest horizontal grid spacing of 1 km. Case 1 in Type 1 occurred on 4 April 2019, which showed a relatively slow upstream flow with high static stability and Froude number (Fr) about 0.7, implying that the acceleration of the flow due to the nonlinear effect by the mountains was the strongest among the cases. There was a strong downdraft on the lee slope, and the flow was separated into the turbulent region and the accelerated one by a wave breaking with strong turbulence. A critical level of a mountain wave was induced by a breaking of a vertically propagating large-amplitude mountain wave in the lower stratosphere, so that the DW was found to be generated by a critical-level reflection of a mountain wave. Case 2 in Type 2 occurred on 19 January 2016. Fr of the upstream flow was about 1.1 and there was an inversion layer near the mountain top level, which was a favorable condition for a hydraulic jump. Inflow in the lower troposphere was accelerated in the downstream by the hydraulic jump in the simulation. Case 3 in Type 3 occurred on 12 November 2011. The upstream flow across the mountains was very strong with low static stability and Fr about 1.6. Acceleration of the inflow by the mountains was likely to be associated with the trapped lee waves in the lower troposphere, in addition to the strong synoptic-scale pressure gradient force.

Shin, Y., J.-H. Kim*, H.-Y. Chun, W. Jang, and S.-W. Son, 2022: Classification of Synoptic Patterns with Mesoscale Mechanisms for Downslope Windstorms in Korea Using a Self-Organizing Map. J. Geophys. Res.: Atmos., 127, e2021JD035867, https://doi.org/10.1029/2021JD035867.

Key Words: Downslope windstorms, Mountain waves, WRF model, Taebaek Mountains

Acknowledgment: This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2019R1I1A2A01060035) and the Korea Meteorological Administration Research and Development Program under Grant KMI2022-00310.