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Influence of the monsoon variability and sea surface temperature front on the explosive cyclone activity in the vicinity of Japan during northern winter


 The possible impact of the winter monsoon intensity and sea surface temperature (SST) gradient on the activity of explosively developing extratropical cyclones around Japan is investigated using the Weather Research Forecasting model. Two independent long-term integrations over 18 winters from 1993/94 to 2010/2011 are conducted using prescribed observed SST data (OS run) and spatially smoothed data (SS run). The OS run is successful in reproducing the spatial distributions of the explosive cyclone activity in the vicinity of Japan under both strong and weak winter monsoon conditions. Under strong monsoon conditions, the Kuroshio, the Kuroshio Extension, and the Japan Sea subpolar fronts give rise to enhanced near-surface baroclinicity through the increase in heat and moisture fluxes from the ocean surface, resulting in frequent occurrence of the explosive cyclone activity along those fronts.

 日本近海で急速に発達する温帯低気圧(爆弾低気圧)の活動に与える冬季モンスーン強度と海面水温(SST)勾配の影響を領域気象モデル(WRF)を用いて評価した。 1993/94年冬季から2010/11年冬季までの18冬季間の長期積分を実行し、下部境界条件として観測されたSSTを与えた実験(OSラン)と勾配を平滑化したSST実験(SSラン)の2種類の 数値実験結果を比較した。OSランはモンスーンの強弱に対応した爆弾低気圧活動を良く再現しており、Yoshiike and Kawamura (2009)の結果と矛盾していなかった。
 モンスーンが強い環境条件下では、黒潮・黒潮続流フロント、日本海亜寒帯フロントが海面からの熱・水蒸気フラックスの増加を通して下層傾圧性を強めており、 結果的にSSTフロントに沿って低気圧活動が活発化することが見出された。  

*Please refer to the following manuscript.
*詳細は下記論文を参照してください。
Iizuka, S., M. Shiota, R. Kawamura, and H. Hatsushika (2013): Influence of the monsoon variability and sea surface temperature front on the explosive cyclone activity in the vicinity of Japan during northern winter. SOLA, 9, 1-4.

fig5.jpg

Fig. 5 (a) Composite map of the horizontal gradient of 900-hPa equivalent potential temperature under the strong monsoon conditions for the OS run, along with the explosive cyclone tracks. The shading interval is 0.5 K/100km. (b) As in Fig. 5a but for the SS run. (c) Composite difference in the horizontal gradient of 900-hPa equivalent potential temperature under the strong monsoon conditions between the OS and SS runs (former minus latter). The shading interval is 0.2 K/100km. (d) As in Fig. 5c but for the surface turbulent heat flux. The shading interval is 20 W m-2.