研究目的
To determine the wavelength trend of propagating swell, offering new insight into the swell dissipation rate for wave modelling.
研究成果
The wavelength of a swell increases when propagating from the storm source but may decrease beyond 10000 km due to interference from local wind in the westerlies from the other hemisphere. Beyond 4000 km, the wavelength can be approximately regarded as constant. These findings suggest that swell dispersion should be considered in swell dissipation calculations.
研究不足
The study is limited by the interference of local wind on the westerlies, which affects the accuracy of wavelength measurements beyond 10000 km. The dispersion of a swell should not be neglected when calculating the swell dissipation.
1：Experimental Design and Method Selection:
The study uses ENVISAT ASAR wave mode data and WaveWatch III (WW3) wave model product to observe and analyze swell wavelength trends. A backward and forward tracing strategy is employed to acquire swell observation sequences.
2：Sample Selection and Data Sources:
ENVISAT ASAR level-2 preprocessed (L2P) Delayed mode (GDR) product from the GlobWave project and hindcast wave information from WW3 forced by wind from the NCEP Climate Forecast System Reanalysis (CFSR) are used.
3：List of Experimental Equipment and Materials:
ENVISAT ASAR, a microwave sensor operating at C band with wave mode for global surface wave observation.
4：Experimental Procedures and Operational Workflow:
Storm sources are determined by calculating the local extremum with a gridded SWH field. Swell tracks are traced forward in space and time from these sources, using specific criteria for selecting SAR swell observations.
5：Data Analysis Methods:
The observed wavelengths are normalized by the wavelength of the source or by the SAR observed wavelength nearest to 4000 km, and linear and nonlinear regression is applied to show the trend.
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