A Study on the Variation of Heavy Snowfall Intensity Associated with the Interaction between Atmosphere and Ocean Surface

Abstract

With the increase in the sea surface temperature (SST) all over the world and around the Korean Peninsula, the atmosphere-ocean interaction in winter is causing frequent heavy snows along the west and south coasts of Korea. The drop in the number of disasters in winter caused by dangerous meteorological phenomena requires forecasting technology based on the synoptic meteorological analysis and meso-scale numerical simulation model. In this study, three recent heavy snow cases in the west and south coasts (continental polar air mass, migratory anticyclone and middle latitude cyclone) were analyzed in view of synoptic meteorology, and three types of SST (NCEP/NCAR SST, RTG SST and OSTIA) sensitivity tests were conducted based on weather research and forecasting (WRF) to interpret the influence of the atmosphere-ocean interaction on the snowfall intensity. The results of the synoptic meteorological analysis showed that when the cold and dry continental high pressure was extended, heavy snow occurred at dawn when the upper atmosphere cooled. In particular, when the continental high pressure was extended and the upper pressure trough passed through, heavy snow occurred due to the convergence region formed in the west coast area, sometimes in the inland of the Honam area. In addition, it was verified that the changes in the humidity coefficients in the upper and lower layers are important data for the determination of the probability, start/end and intensity of heavy snow. However, when the area was influenced by the middle-latitude low pressure, the heavy snow was influenced by the wind in the lower layer (925 hPa and 850 hPa), the equivalent potential temperature, the convergence field, the moisture convergence and the topography. SST sensitivity tests were conducted for the two cases of heavy snow in the west and south coasts of Korea (Extension of continental high pressure, 30 December 2010, Case 2010; and Effect of migratory low pressure, 28 December 2012, Case 2012). The results showed that NCEP/NCAR SST was generally balanced by latitude, but OSTIA and RTG SST were distributed along the coastline. Because NCEP/NCAR SST was excessive simulated for the west coast area prior to the SST sensitivity test, the snowfall was also excessive simulated. In Case 2010 (30 December 2010), OSTIA had the best numerical simulation with diverse atmospheric conditions, and the maximum difference in the numerically simulated snowfall between NCEP/NCAR SST and OSTIA was 20 cm. Although there was a regional difference in the snowfall according to the difference in the SST in the OSTIA and RTG SST numerical tests, it was not as significant as in the previous results. A higher SST led to the numerical simulation of larger snowfall, and the difference was greatest near Buan in the west coast area. Case 2012 (28 December 2012) had a smaller difference in snowfall according to the SST than Case 2010. However, the numerically simulated snowfall based on NCEP/NCAR SST and OSTIA significantly differed near Jiri Mountain due to the topographical effect, and the difference was 1-2 cm in other areas. In addition, in the sensitivity test with OSTIA and RTG SST, the spatial difference of the snowfall was less than 1 cm. When the low pressure that developed in the south sea passed the Korean Peninsula, it passed through the warm south sea and caused precipitation rather than snowfall, and it did not significantly influence the snowfall after it reached the land. Its influence was also limited to the coastline in the west sea. Thus, SST was found to be a very important factor of the heavy snowfall in the west and south coasts. In the case of snowfall due to a low atmospheric pressure, it is expected that the snowfall development mechanism will be identified while considering not only the two-dimensional SST distribution but also the topographical factors and the types of precipitation.