Sensitivity of Snowfall Characteristics to Meteorological Conditions in the Yeongdong Region of Korea

Abstract

This study investigates the characteristics of cold clouds and snowfall in both the Yeongdong coastal and mountainous regions under different meteorological conditions based on the integration of numerical modeling and three-hourly rawinsonde observations with snow crystal photographs for a snowfall event that occurred on 29–30 January 2016. We found that rimed particles predominantly observed turned into dendrite particles in the latter period of the episode when the 850 hPa temperature decreased at the coastal site, whereas the snow crystal habits at the mountainous site were largely needle or rimed needle. Rawinsonde soundings showed a well-defined, two-layered cloud structure along with distinctive wind-directional shear, and an inversion in the equivalent potential temperature above the low-level cloud layer. The first experiment with a decrease in lower-layer temperature showed that the low-level cloud thickness was reduced to less than 1.5 km, and the accumulated precipitation was decreased by 87% compared with the control experiment. The difference in precipitation amount between the single-layered experiment and control experiment (two-layered) was not so significant to attribute it to the effect of the seeder-feeder mechanism. The precipitation in the last experiment by weakening wind-directional shear was increased by 1.4 times greater than the control experiment specifically at the coastal site, with graupel particles accounting for the highest proportion (∼62%). The current results would improve snowfall forecasts in complicated geographical environments such as Yeongdong in terms of snow crystal habit as well as snowfall amount in both time and space domains.

摘 要

结合数值模拟和3小时探空仪与雪晶照相观测,针对2016年1月29日至30日的降雪过程,本文研究了不同气象条件下,韩国永东沿海地区和山区的冷云降雪特征。作者发现,沿海站点850 hPa温度在降雪过程后期下降时,雪晶形状从凇附粒子主导变成以枝状粒子为主,而山区站点雪晶形状主要是针状或凇附针状。探空观测显示,本次降雪过程存在两层云结构,并伴随显著的风切变和低层云层上方的相当位温逆温。第一个低层温度降低的敏感性试验与参照试验相比,低层云厚减小到1.5 km以下并且降水量减少87%;第二个单层云试验和参照试验(两层云)相比,由于播种-供给机制的影响,降水量差异不明显;最后一个减弱风向切变的敏感性试验与参照试验相比,降水量增加1.4倍,沿海站点的霰粒子占比高达~62%。目前的研究结果将有助于改善复杂地形环境下(例如韩国永东)的降雪预报,包括对雪晶形状和降雪量时空分布的预报。