Abstract
Statistical characteristics and composite synoptic-scale environmental conditions of explosive cyclones (ECs) over the Japan Sea and Kuroshio/Kuroshio Extension are examined and compared using ERA5 atmospheric reanalysis to give a better understanding of their differences. ECs over the Japan Sea frequently occur in late autumn and early winter and those over the Kuroshio/Kuroshio Extension mainly occur in winter and early spring. The maximum deepening rate, minimum central sea level pressure and explosive-developing lifetime of ECs over the Kuroshio/Kuroshio Extension are generally larger, lower and longer, respectively, than those over the Japan Sea. ECs over the Kuroshio/Kuroshio Extension formed over the East China Sea tend to develop more rapidly, and weak and moderate ECs generally begin to develop explosively over the sea to the east of the Japan Islands, while the strong and super ECs over the sea to the south of Japan Islands have longer explosive-developing tracks. Composite analysis shows that synoptic-scale environmental conditions favoring rapid EC development over these two regions are significantly different. ECs over the Japan Sea have stronger baroclinicity and cyclonic vorticity, but weaker water vapor convergence and upper-level jet stream than those over the Kuroshio/Kuroshio Extension. The key factor contributing to the baroclinicity is the cold air intrusion over the Japan Sea and the strong warm current heating over the Kuroshio/Kuroshio Extension. The potential vorticity shows anomalies in upper and low levels for both EC areas and extends further downwards over the Japan Sea.
Highlights
Explosive cyclones (ECs) are rapidly developing cyclonic systems whose central sea level pressure (SLP) drops more than or equal to 24 hPa within 24 h when adjusted geostrophically to 60◦ N [1]
The patterns of frequency distribution over these two areas are significantly different, with 45.3% ECs over the Japan Sea occurring in late autumn (November) and early winter (December) and 82.2% ECs over the Kuroshio/Kuroshio Extension occurring in winter (December, January and February) and early spring (March)
Results show that the Japan Sea and Kuroshio/Kuroshio Extension have the highest EC occurrences over the northern Pacific (Figure 1)
Summary
Explosive cyclones (ECs) are rapidly developing cyclonic systems whose central sea level pressure (SLP) drops more than or equal to 24 hPa within 24 h when adjusted geostrophically to 60◦ N [1]. Chen et al [13] and Yoshida and Asuma [8] pointed out that the Japan Sea and the northwestern Pacific along the Kuroshio/Kuroshio Extension are two favorable areas for rapid EC development. Yoshida and Asuma [8] and Zhang et al [2] suggested that the occurrence frequency of ECs shows evident seasonal variations for various regions over the northern Pacific; ECs over both the Japan Sea and the Okhotsk Sea peaked in November, whereas the maximum EC frequency over the northeastern Pacific is in January in Yoshida and Asuma [8] and December in Zhang et al [2]. Other statistical features over the Japan Sea and Kuroshio/Kuroshio Extension, such as the minimum SLP, explosive-developing lifetime, etc., are rarely examined
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