Analysis on the temporal and spatial distribution of the wave height during Typhoon RANANIM with altimeter data

To improve the monitoring and forecasting of typhoon wave height,is an important measure to mitigate typhoon disasters.At present,typhoon waves are obtained by numerical simulation.But due to the applicability of the model itself and the inaccuracy of the initial forecasting field,the resulted wave heights are relatively low compared to the satellite data.The development of satellite altimetry provides powerful information for the study of wave height fields.The significant wave height data from GFO,TOPEX/Poseidon,Jason-1 and Envisat are merged to analyze the temporal and spatial features of the wave height of Typhoon RANANIM,and the relationships between the wave height and the wind speed are studied with QuickSCAT data.The amalgamated data used here are the effective wave height data collected by GFO,TOPEX/Poseiden\Janson-1 and Envisat in August 5~13,2004 and method of successive correction is used.The key of this method is to determine the initial guess wave field and to choose the radius.The initial guess field is based on surface fitting method.The initial radius R is determined according to the study region and the spatial scale of significant wave height.As the moving path of typhoon is basically in the mid-latitude region and the spatial scale of wave induced by typhoon is great,1 000 km is selected the initial radius R.With the increase of the number of iteration R deceases with a reducing step of 200 km and the number of iterations is 3 or 4.At the same time,since the fusion results are influenced by the size of filter windows,the one-day wave field is needed and the amount of data is relatively scarce,tests show that 11×11 filter window size would be proper when the grid size is 0.5°×0.5°.It is shown that(1) the fusion results could reveal the moving path of the typhoon;(2) as RANANIM evolved from a tropical storm into a powerful typhoon,the wave height was getting higher and higher,with the average from 5.5 m to 8.5 m and the maximum from 6.5 m to 10.6 m;(3) the spatial distribution of wave height is basically in accordance with the center of typhoon;(4) the range and radius of wind speed over 15 m/s is in accordance with that of wave height over 3 m.