Microphysical Characteristics of Snowfall in Seoul, South Korea and Their Changes with Meteorological Conditions

Abstract

In this study, the microphysical characteristics of snowfall in Seoul, South Korea and their changes with meteorological conditions are examined using about 6-year observation data from a Parsivel disdrometer. The snow particle size distribution (PSD) exhibits convex-down shapes, being better represented by gamma distributions than exponential distributions. As snowfall rate increases, the snow PSD broadens and its peak rises. The changes in gamma PSD parameters with snowfall rate differ between the mean PSD and 1-min PSDs. The volume-weighted mean diameter D_m much more rapidly increases with snowfall rate in comparison with D_m in Beijing, China and Pyeongchang, South Korea, suggesting the relative importance of aggregation in Seoul. 77% of snowfall in Seoul occurs when northwesterly blows at the 850-hPa level. This snowfall is associated with west-high/east-low pressure patterns, large air–sea temperature differences (~ 19 °C), and shallow (≤ 2.5 km) precipitation systems, suggesting a large contribution of sea-effect snowfall from the Yellow Sea. The northwesterly-type snowfall with lower temperatures (≤ 25th percentile, COLD) and with higher temperatures (≥ 75th percentile, WARM) at the 850-hPa level is compared in the same intensity range of 0.5–1 mm h⁻¹. Compared with the WARM snowfall, the COLD snowfall has relatively broad PSDs and less-rimed snow particles. The COLD snowfall is associated with relatively large wind shear, small static stability, low temperatures of − 21 to − 9 °C, and low humidity in the lower atmosphere, which is attributed to relatively strong northwesterly resulting in relatively strong cold and dry advection. This implies that enhanced aggregation by stronger turbulence and dendritic growths can contribute to the broader PSDs and that weakened riming for the lower temperatures might be associated with the less-rimed snow particles.