CHGS method for numerical forecasting of typhoon waves——Ⅰ. Spectrum of waves in growing phase

Owing to the fact that the wind speed and direction of typhoon vary rapidly with time and space in typhoon fetch; the nearer to the typhoon eye the greater the wind velocity, and the shorter the wind fetch the smaller the wind time,as a result,the more difficult for the wind wave to fully grow.Hence.in typhoon wave numerical calculation it is impossible to use the model for a fully grown wave spectrum.Lately, the author et at.presented a CHGS method for numerical forecasting of typhoon waves, where a model for the growing wave spectrum was set up (see Eq.(2) in the text).The model involves a parameter indicating the growing degree of wind wave, i.e., the mean wave age β.When βvalue is small, the wave energy is chiefly concentrated near the peak frequency, so that the spectral peak gets hi gh and steep; with the increase of β the spectral shape gradually gets lower and gentler; when β=Ⅰ, the wave fully grows, the growing spectrum becomes a fully grown P-M spectrum.The model also shows a spectral "overshooting" phenomenon within the "balance zone".