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

Abstract

An investigation was conducted to describe the locations of initial occurrence, evolution and structure of meso-α-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-α-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-α-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.

Environment and Processes for Heavy Rainfall in the Early Morning over the Korean Peninsula during Episodes of Cloud Clusters Associated with Mesoscale Troughs

“…A heavy rainfall episode is defined by a 24-hour rainfall amount greater than 80 mm at a minimum of one station. Seventeen CCMT episodes have been selected for the 11-year period based on the definition of CCMTs by Shin and Lee (2015) (Table 1). It can be found from Table 1 that the maximum hourly rainfall amount occurs mostly during 0000 -1200 LST (LST = UTC + 9 hours) in 14 episodes, where 10 of them have maxima during 0300 -0900 LST (1800 -0000 UTC).…”

“…Heavy rainfall over the Korean peninsula during summer generally occurs over or near the northwestern edge of the western Pacific subtropical high (WPSH), where a wide band of southwesterlies can be found. As a meso-α-scale depression moves or develops along the northwestern edge of the WPSH, southwesterlies to the southeast of the depression become stronger (Shin and Lee 2015). Various studies have also found the importance of strong southwesterlies or low-level jets (LLJs) for heavy rainfall over the Korean peninsula (e.g., Kim et al 1983;Hwang and Lee 1993;Chen, S. et al 1999;Jung et al 2018).…”

“…A CC is defined as an oval-shaped cloudmass region, with an equivalent black-body temperature (TB) lower than -50°C, that is approximately larger than 100 km in diameter (Takeda and Iwasaki 1987;Lee and Kim 2007). Shin and Lee (2015) found that CCs over the Korean peninsula were associated with mesoscale depressions in the lower troposphere: 64 % of CCs were associated with meso-α-scale lows (CCMLs), which mainly originated from China, whereas 31 % of CCs were associated with mesoscale troughs, which mostly formed over the Yellow Sea and the west coast of the Korean peninsula. They used the term "mesoscale trough" for a mesoscale depression that did not develop into a system with a meso-αscale closed isobar.…”

Atmospheric Structure for Convective Development in the Events of Cloud Clusters over the Korean Peninsula

“…Cloud clusters are the major type of MCSs over the Korean peninsula, and Shin and Lee (2015) classified CCs into two types: those associated with meso-α-scale lows (CCMLs) and mesoscale troughs (CCMTs). The term "mesoscale trough" defines a mesoscale depression that does not develop into a meso-ɑ-scale closed-isobar system.…”

Domain‐size and top‐height dependence in regional predictions for the Northeast Asia in spring

“…For Northeast Asia, choosing a wide model domain may make the Tibetan Plateau (TP), Manchuria and the Kamchatka Peninsula (MK) included in the model domain. The TP can induce peculiar air flows due to strong radiative forcing related to its high elevation and vigorous dynamical forcing in steep slope regions at the lee side and stagnation regions over the eastern flank at the Sichuan Basin (SB) (e.g., Jiang, Li, Zhao, & Koike, ; Shin & Lee, ; Tao & Ding, ; Wang & Orlanski, ). Numerical simulations of such unique flow structures are challenging, and inaccurate simulations may produce unreliable predictions for Northeast Asia (Zhang, Li, Fu, Liu, & Li, , and references therein).…”