A numerical simulation of a strong windstorm event in the Taebaek Mountain Region in Korea during the ICE-POP 2018

Abstract

During the International Collaborative Experiments for the Pyeongchang 2018 Olympic and Paralympic winter games (ICE-POP 2018), a strong windstorm occurred on the lee side of the Taebaek Mountains on 14 February 2018, when a low-pressure system passed through the northern part of the Korean Peninsula. At that time, a prevailing westerly wind with warm advection and an inversion layer at the top of the mountains provided favorable conditions for the downslope windstorm, resulting in structural damage at the Olympic Park. This led to the delay and cancellation of the ski jump and biathlon games. To investigate the generation mechanism responsible for the downslope windstorm during the ICE-POP 2018, we performed a numerical simulation using the Weather and Research Forecast model with the finest horizontal grid spacing of 333 m. The model effectively reproduced the multi-scale flows, such as the synoptic-scale low-pressure system, upstream sounding, and downslope winds, with slightly overestimated surface winds at some local sites on the lee side. Analysis of vertical cross-sections across the mountains showed a steep descent of potential temperature on the lee slope and a rapid recovery on the leeward side, showing the evidence of hydraulic jump with a Froude number of 0.9. During the windstorm event, mountain waves were generated with horizontal wavelengths that varied with time due to the change in background wind and stability along with movement of the low-pressure system. Using the dispersion relationship for internal gravity waves, the Scorer parameter for quasi-stationary mountain waves showed that the waves with horizontal wavelengths smaller than 10 km were trapped below the altitudes of 6–9 km. There were no signals of mountain wave breaking and wind reversal with height (wave-induced critical level), implying that the downslope windstorm event was generated by the mechanisms of hydraulic jump and partial reflection. Strengthened jet streams in the upstream and inversion layers at the top and gap winds in the valleys of the mountains also facilitated the downslope winds on the lee side.