[A-CG32] Extratropical oceans and atmosphere

[ACG32-P04] Atmospheric and Oceanic Conditions for the Strong Wintertime Cyclones in the Kuroshio Extension Region

*Taisei Ogawa¹, Masanori Konda¹, Akira Kuwano-Yoshida² (1.Graduate School of Science, Kyoto University, 2.Disaster Prevention Research Institute, Kyoto University)

Keywords:Extratropical Cyclone, East China Sea, Large-scale Atmospheric Circulation, Surface Heat Flux, Sea Surface Temperature, Statistical Analysis

We investigated the atmospheric and oceanic conditions in the early stage of wintertime extratropical cyclones which tended to develop rapidly in the Kuroshio Extension region. As most of such cyclones were generated over the East China Sea, we studied in detail the background fields as well as the structure of the cyclones formed over that region. At first, we classified the cyclones into three categories based on their intensities and tracks; strong, moderate, and weak types, respectively. The strong and the moderate types could be distinguished from the weak one by the warm and moist airflow caused by the lower-level anticyclone to the east of the formation region. It was also suggested that the formation of the anticyclone was influenced by the upper-level wave propagation related to the sea surface temperature in the South China Sea. The difference between the strong and the moderate types could be attributed to the strength of evaporation, which was enhanced by the advection of the cold and dry atmosphere from the northwest because of the upstream trough. Moreover, the evaporation in the southwest portion of the strong type cyclones became larger than that of the moderate ones, when they crossed the oceanic front between the Kuroshio and the East China Sea. These discrepancies between the conditions in the early stage of the strong and the moderate types possibly led to the difference in the total amount of the latent heat flux, and therefore the strength of the cyclones, before reaching the Kuroshio Extension region. These results suggested that the strength of cyclones in the Kuroshio Extension region could be influenced by the atmospheric and oceanic conditions in the early stage of their development.