Evidences of Typhoon/Hurricane Swell Doppler Effect

摘要

The typhoon/hurricane determines usually the designed wave for maritime structures. According to all wave hindcast techniques, the typhoon/hurricane wave is mainly influenced by the central pressure and the radius of maximum wind speed, i.e. the strength of typhoon/hurricane. There is only a minor effect due to the moving speed. However, a distant typhoon/hurricane may generate very high swell height as the typhoon/hurricane is approaching a station(Liang, 2003). This is explained through the wave energy flux increase, which is the same as the well-known Doppler effect. The wave height modification factor ? is equal to (TD / TD’)1/2 , in which TD is the swell appearance time period for a stationary typhoon and TD’ that for a moving typhoon. TD’ is less than TD as the typhoon is moving to the wave station. Once TD’ is negative, the latter wave overruns the former one. Then ? is assumed to be 1.414, as it is due to the typhoon strength increase. This is based on the energy superposition of two equal wave height components. ? is assumed to be 4, as it is due to the typhoon approaching speed. As TD’ is much smaller than TD , ? may be very large. In this paper, ? is also assumed to be less than4. These assumptions are basically empirical.