利用海氣耦合模式(COAWST)研究颱風以及黑潮在台灣東部外海之交互作用

In this work, the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) model is used to hindcast typhoon Haiyan (2013), an extremely intense tropical cyclone striking Philippine in 2013. Given the record breaking intensity of Haiyan, the upper ocean condition underlying the severe storm is considered as relative favorable for storm intensification, in addition to existing favorable atmospheric conditions, which have been reported and confirmed in previous studies. However, out of expectation, our simulations indicate a systematic result (despite of model setting/coupling complexity) that Haiyan is not the combination/synergy of “worst conditions” from both atmospheric and oceanic frames. On the contrary, our results shed light on a possibility that Haiyan might have an even worse situation (develop to be more violent storms), given identical (favorable) atmospheric conditions. Subsequently, this possible over intensify is diagnosed/shown to be associated with an extra horizontal heat advection (U·▽T) resulting mainly from extremely strong current contributions tied to unusually northward shift of North Equatorial countercurrent (NECC) in La Nina years. The results shown in this study imply a horrible/inconceivable/inconvenient result that category-6 might not the real ceiling as our understanding for the present stage.