Variability in the Microphysical Characteristics Associated with Orographic Airflow in the Mountainous Pyeongchang Region

Abstract The Wind Synthesis System using Doppler Measurements (WISSDOM) was used to retrieve the fine-scale structural evolution of airflow and precipitation over complex terrain in the Pyeongchang region, South Korea, during the passage of a low pressure system (LPS) in winter. The objective of this study is to investigate the variability in microphysical characteristics and their relationships with orographically modified three-dimensional winds. The Micro Rain Radar (MRR) and laser-optical disdrometer Particle Size Velocity (PARSIVEL) were deployed at the two stations (YPO and CPO) to collect microphysics observations. The YPO (CPO) station is located on the southwestern (northeastern) side of the Pyeongchang branch with a relatively gentle (steep) slope. The study period could be divided into two stages (stages I and II) based on the changes in prevailing wind directions and precipitation patterns associated with the LPS. The results indicated that the orographically modified airflow was dominated by southwesterly (northeasterly) winds along the Pyeongchang branch during stage I (II). Compared to the YPO, the CPO always had a much higher precipitation rate and higher concentrations of larger particles in this case. The enhanced precipitation at the CPO was related to the southwestern (northeastern) winds in stage I (II) and was also significantly influenced by vertical winds. In stage I, although the numbers of particles have positive relationships with southwesterly winds both at the YPO and CPO, alternating updrafts and downdrafts appear to have accelerated the growth of particles with efficient aggregation processes only at the CPO. In stage II, relatively stronger updrafts were potentially triggered by the impinging northeasterly winds, which helped to generate heavier particles by riming at the CPO. Although there is a short distance between the YPO and CPO stations (∼10 km), the changed airflow associated with moving LPS is a key factor causing the variability in microphysical characteristics and precipitation in the Pyeongchang region. Significance Statement This study examines the variability in microphysical characteristics and their relationships with orographically modified three-dimensional (3D) winds. The fine-scale structural evolution of airflow and precipitation over complex terrain can be documented in the Pyeongchang region, South Korea, during the passage of a low pressure system (LPS) in winter. Although there is a short distance between the two analyzed stations (∼10 km), the changed airflow associated with moving LPS is a key factor causing the variability in microphysical characteristics and precipitation.