溫帶氣旋湧浪預報初步研究

Abstract

美國、加拿大和阿拉斯加太平洋沿岸有時可以看到非常大的湧浪，湧浪的群速度很大，所以波高大的湧浪，他的能量通率也就很驚人，其破壞力不容忽視。過去有郵輪被海浪損毀的事件，因為溫帶氣旋是移動性風域，可能會如颱風產生巨大的突發的怪浪(Freak wave)，也許可以解釋一些無颱風時發生的海難，所以研究溫帶氣旋的湧浪推算是有意義的。 因為NWW3模式計算湧浪的結果不準，波高及週期都偏小。本研究探討北太平洋上的溫帶氣旋所造成的湧浪時，採取兩種方式：其一為SMB法，其二為NWW3經驗法。前者作法是，先決定風場的參數，再利用計算出風場的參數資料以SMB法求出波高及週期，利用能量守恆的原理，考慮傳遞距離以及角度擴展等因素求得波浪的到達時間及波高週期大小；後者作法是，先利用NWW3模式計算出波浪場的波高、週期及波向，如同前方法利用能量守恆的原理，考慮傳遞距離以及角度擴展等因素求得波浪的到達時間及波高週期大小。 結果得到使用SMB法時風場位置需選擇風場前緣；篩選風速資料時使用0.7倍最大風速為最佳；使用NWW3經驗法時波源位置需選擇0.9倍最大波高的浪場前緣；推算結果是以NWW3經驗法為較佳。

The huge swell sometimes happens in the Pacific Ocean along Alaska, Canada and America .The group velocity of swell is very large, then energy flux is amazing. The destructive power could not be ignored. Liners were damaged in the past. The Extra-Tropical Cyclone moves as a typhoon and may make Freak wave. It can interpret shipwrecks when there were no typhoon. Therefore, it is worth to study the extra-tropical cyclone swell forecasting . The result of NWW3 wave model is not accurate in forecasting swell, the wave height and the period are rather small. There are two kinds of methods: One is called SMB method, and the other is NWW3 method. In the former, parameters of wind field are determined first. Then the wave height and the period in the wind field are estimated by the SMB method. By using the energy conservation law and considering the distance and the angular spreading, empirical equqtions are obtained. For the latter the wave field is estimated by NWW3 at first. Then following the same principle, different empirical equqtions are obtained. As the result, it is better to use the front of wind field and the wind velocity larger than 0.7 times the maxinum in the SMB method. It is better to use the front of wave field and the wave hight larger than 0.9 times the maxinum in the NWW3 method. NWW3 method is better on swell forecasting.