An East Asian Cold Surge: Case Study

Abstract
Since a cold surge is a hazardous weather phenomenon in east Asia, the rapid population increase and economic growth over the past two decades require improvement in forecasting cold surges and their related weather events over this region. However, without a better understanding of these events, this task cannot be accomplished. A cold surge with a well-defined cold front passing through Taiwan was selected to illustrate its impact on the east Asian weather system. This case is typical of a large portion of surges occurring in the region. Major findings of this study are as follows. Coupling with the upper ridge–trough structures of the wave train straddling the eastern seaboard of northeast Asia, cold surges occur sequentially. A cold front with a prefront high pressure zone is formed by the new surge outflow interacting with the anticyclone of the aging surge. The warm moist air advected northeastward along the cold front assists the development of the new surge's low center, while the prefront high pressure zone facilitates the formation of a double-cell structure in the local Hadley circulation. The southeastward propagation of the cold front is driven by the eastward-propagating short-wave trough through the couplets of both new and aging cold surges. The surface weather conditions in the low-elevation zones of Taiwan are modulated by the cold surge flow, but the high-elevation areas may be affected instead by the tropical southeast Asian high. Despite the success of the prior and post-WMONEX (Winter Monsoon Experiment) research in exploring the tropical–midlatitude interaction, the close interaction of cold surges with local weather systems and the planetary-scale circulation in east Asia, illustrated by the case study presented, provides another dimension of cold surge research.