Origin, evolution and structure of meso-α-scale lows associated with cloud clusters and heavy rainfall over the Korean peninsula

An investigation was conducted to describe the locations of initial occurrence, evolution and structure of meso-alpha-scale lows (MLs) associated with cloud clusters and heavy rainfall over the Korean Peninsula using observation and reanalysis data. We selected 29 heavy rainfall events associated with MLs during the 10-year period of 2001-2010. The locations of initial ML occurrence are widely spread from the eastern flank of the Tibetan Plateau to the Yellow Sea. These locations are grouped into 3 regions: 1) the eastern flank of the Tibetan Plateau (R1, 6 cases), 2) central and eastern China (R2, 16 cases), and 3) the Yellow Sea (R3, 7 cases). Initial MLs tend to occur within a deep trough over the eastern flank of the Tibetan Plateau (R1 cases) or a long trough extended northeastward from the southeast of the Tibetan Plateau along the northwestern rim of the western Pacific subtropical high (a majority of R2 cases and two R3 cases). Horizontal temperature gradients are weak over the areas of initial MLs. Meso-alpha-scale lows tend to develop in the lower troposphere (e.g., below 700 hPa) in an environment of existing cyclonic vorticity. And they are accompanied by anticyclonic vorticity in the upper troposphere. The speed of ML movement varies with each case and with the location of ML. The average speeds of ML movement are 32.4, 37.2 and 40.4 km h(-1) for the R1, R2 and R3 groups, respectively. Meso-alpha-scale lows are shown to have a warm-core structure in general. They are tilted toward various directions with a majority of them (14 of 29 MLs) tilting northward with height.