Association Between Upstream Conditions and the Intensity of Orographic Precipitation in the Main Mountain Ranges of South Korea

Abstract

This study uses high temporospatial surface precipitation rate obtained from radar observations (hybrid surface rainfall, HSR), 3D winds retrieved from the Wind Synthesis System using Doppler Measurements (WISSDOM), and 3D thermodynamic fields to investigate the association between orographic precipitation and upstream conditions for the main mountain ranges of South Korea during the 2018–2020. The main objective was to determine the dominate meteorological factors affecting the rain intensity over this terrain. Three rainfall cases were analyzed covering western, and eastern slopes of the Taebaek mountain range (TMR), Mt. Jiri, and Busan City. Correlation coefficients ($R$) were used to evaluate the strength of the relationship between rain intensity and meteorological factors in these regions, including the wind directions, wind speed, Froude number, saturated Froude number, water vapor, moist flux, stability, vertical velocity, and convergence. The results revealed that the wind direction determined the location of precipitation in the mountains, with the wind speed and moist flux identified as the most influential factors for rain intensity, with high correlation coefficients of 0.55–0.85. The upstream Froude number appeared to modulate the orographic enhancement on rain intensity over Mt. Jiri and the western slopes of the TMR. Low-level convergence was another critical factor affecting the rain intensity along the northeastern coast of South Korea (i.e., the eastern slopes of the TMR) and Busan ($R$ of ∼0.6–0.7). Statistical analysis of all orographic precipitation cases (52 cases over the 3 years) revealed that the upstream wind speed, and moist flux in the mid-layers had a higher correlation with rain intensity over the western slopes of the TMR and Mt. Jiri. The relationship between rain intensity and both water vapor and low-level convergence was also stronger along the northeastern coast of South Korea.