High-Resolution Simulation of Snowfall over the Korean Eastern Coastal Region Using WRF Model: Sensitivity to Domain Nesting-Down Strategy

摘要

The eastern coastal area of the Korean Peninsula, Yeongdong region, often experiences severe snowfall during the winter season. We studied the development mechanism of a snowfall case occurred in February 2014 using the Weather Research and Forecasting (WRF) model at the convection-permitting resolution of 1km. The model reasonably captured the observed snowfall, and three factors were discovered as important contributors to this snowfall case: a temperature contrast between land and ocean, a high-pressure system over the northeastern part of the Korean Peninsula, and the mountainous terrain. Cold and dry air blown from the high-pressure system gains heat and moisture when it passes over the East Sea enhancing the low-level instability. When the air mass reaches the coastline, updraft is generated by the density difference with the continental atmosphere and by the mountain slope. Further sensitivity experiments were conducted by adjusting strategies of nesting down (offline and online). Sensitivity experiments consist of three offline nesting experiments with different boundary condition update frequencies in 6, 3 and 1h and one online nesting experiment that updates the boundary condition every integration time step. The major snowfall along the mountain range located in the middle of domain does not change significantly regardless of the nesting frequency. The offline nesting causes unphysical discontinuities of precipitation along the north and east sides of lateral boundary where wind blows in, which are caused by the absence of condensed hydrometeor variables in the lateral boundary condition. The domain nesting strategy tested in this study has dramatically impacted on the upper troposphere structure in the model: artificial fluctuations at the upper troposphere in the offline nesting simulations were significantly alleviated in the online nesting simulation.