Abstract
A flood-producing heavy rainfall event occurred at the mountainous coastal region in the northeast of South Korea on 5–6 August 2018, subsequent to extreme heat waves, through a quasi-stationary mesoscale convective system (MCS). We analyzed the storm environment via a multi-data approach using high-resolution (1-km) simulations from the Weather Research and Forecasting (WRF) and in situ/satellite/radar observations. The brightness temperature, from the Advanced Himawari Imager water vapor band, and the composite radar reflectivity were used to identify characteristics of the MCS and associated precipitations. The following factors affected this back-building MCS: low-level convergence by the Korea easterlies (Kor’easterlies), carrying moist air into the coast; strong vertical wind shear, making the updraft tilted and sustained; coastal fronts and back-building convection bands, formed through interactions among the Kor’easterlies, cold pool outflows, and orography; mid-level advection of cold air and positive relative vorticity, enhancing vertical convection and potential instability; and vigorous updraft releasing potential instability. The pre-storm synoptic environment provided favorable conditions for storm development such as high moisture and temperature over the coastal area and adjacent sea, and enhancement of the Kor’easterlies by expansion of a surface high pressure system. Upper-level north-northwesterly winds prompted the MCS to propagate south-southeastward along the coastline.
Highlights
The eastern coastal region of South Korea has complex terrain with a narrow coastal area surrounded by the East Sea/Sea of Japan and a steep and long mountain range parallel to the coastline
At upper levels (Figure 3; middle and bottom panels), the Korean Peninsula was generally under the influence of a ridge with a warm-core high lingered over the Yellow Sea
We investigated a heavy rainfall event (HRE) that caused flash flooding at the mountainous coast in the northeastern part of South Korea, called Yeongdong, which was produced by a quasi-geostationary/back-building mesoscale convective system (MCS) with tapering cloud rarely observed in this region
Summary
The eastern coastal region of South Korea has complex terrain with a narrow coastal area surrounded by the East Sea/Sea of Japan (hereafter, ES) and a steep and long mountain range parallel to the coastline. This region, named Yeongdong, often experiences hazardous weather phenomena—generally associated with transport of moist air from the ES by the so-called “Korea easterlies” (hereafter, the Kor’easterlies), and their associated orographic lifting (e.g., [1,2,3,4]). Sometimes they present a tapering cloud system, encompassing deep cumulonimbi (usually brightness temperature TB < −40 ◦C) that form at an upwind base tip and spread horizontally to the downwind side one after another (i.e., back-building): heavy rainfall concentrates on a specific area when this system stagnates or travels slowly [12]
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