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Response of extratropical cyclone activity to the Kuroshio large meander in northern winter

 We examined possible responses of cyclone activities to the bimodal path states of the Kuroshio Current (i.e., large-meander (LM) and non-LM (NLM)) by using the long-term reanalysis data and the twentieth century hindcast experiment of atmosphere-ocean coupled model. Compared with a seasonal mean cyclone track frequency for the LM and NLM periods, a primary cyclone track shifts southward in association with the meander of Kuroshio Current. Composite analyses of the hindcast experiment showed remarkable atmospheric responses accompanying the Kuroshio LM. The Kuroshio LM causes a decrease in latent heat flux in the south of Japan and a southward shift of the near-surface baroclinic zone. Distinctive decreases in thermodynamic fluxes inhibit the rapid development of cyclones in the meander region, eventually inducing positive sea level pressure anomalies downstream from that region.

 大蛇行時と非大蛇行時を比較すると、黒潮が大蛇行している時には(所謂、南岸)低気圧の主経路は南偏しており、大気海洋結合モデルで再現された黒潮の大蛇行においても同様な大気応答が 生じていることが見出された。黒潮の大蛇行は日本南岸の潜熱フラックスを減少させると共に、地表付近の傾圧帯の南方への遷移の原因となっている。海面熱フラックスの著しい減少は 黒潮大蛇行海域の低気圧の急速な発達を抑制し、結果的に下流側の海面更正気圧の上昇をもたらしている。  

*Please refer to the following manuscript.
Hayasaki, M., R. Kawamura, M. Mori, and M. Watanabe (2013): Response of extratropical cyclone activity to the Kuroshio large meander in northern winter. Geophysical Research Letters, 40, doi:10.1002/grl.50546


Figure 3. Composite cyclone frequency (unit: count/month) in the 10 cold seasons (DJFM) for the Kuroshio (a) LM and (b) NLM period. Area enclosed by thick dashed line is used to determine a primary path of cyclones (triangles). Solid lines over ocean denote the composite SST (CI = 2℃).