A study on the diurnal variation of the snowfall structure in the western coastal region of the Korean Peninsula.

 On the western coastal region of the Korean Peninsula in the winter, heavy snowfall occurs due to air mass modification which is called the western coast snowfall. The western coast snowfall occurs through a mechanism similar to the lake effect snowfall that is formed over the Great Lakes in the North America. In the winter season, cold and dry northwesterly wind blowing from the south-eastern flank of the Siberian High is formed over the Yellow Sea. The cold and dry air mass from the continent gets heat and moisture from the ocean when it passes over the relatively warm sea surface, , which invigorate snow clouds. The snow clouds generated over the ocean flow into the western coastal region by the westerly winds, hence predicting when the snow clouds flow into the land is important for snowfall forecast. Although the western coast snowfall can persist for several days when the synoptic environment is maintained, diurnal fluctuations in snowfall inflow appears during the snowfall cases. In this study, the diurnal variation of snowfall inflow on the western coastal region was investigated by analyzing of the dynamic/thermodynamic factors affecting the diurnal variation. The western coast snowfall shows snowfall inflow into the land in the evening, then inflow decreases after sunrise, with the snowfall becoming concentrated over the ocean, and the snowfall inflow increases after sunset. The diurnal variation of the snowfall inflow structure appears with the diurnal variation of the dynamic/thermodynamic structure according to the solar radiation diurnal cycle. During the evening, as the temperature of the lower troposphere over the land decreases due to radiative cooling, the lower troposphere thermal stability increases. After sunrise, the planetary boundary layer (PBL) height grows due to radiative heating, and the wind in the lower troposphere weakens, limiting the snowfall inflow to 9 LST, where both factors affect simultaneously. In addition, as the lower troposphere temperature over the land decreases, the land-sea horizontal temperature contrast increases, and the density wall of the colder land blocks the inflow of the snowfall. On the other hand, during the daytime, the lower troposphere temperature of the land rises due to radiative heating and the thermal stability decreases. As the horizontal temperature contrast decreases and the PBL height decreases after sunset, the lower troposphere wind becomes stronger, which allows the snowfall penetrates into the land. According to the time lag in heating/cooling by radiation of the lower troposphere, it is analyzed that the time point of snowfall inflow interruption (increasing) appears after sunrise (sunset).

 

Acknowledgement

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government(MSIT) (No. 2021R1A4A1032646).