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The wave spectral properties in the centimeter to decameter (cmDm) wavelengthrange is of great interest to ocean remote sensing and studies of ocean surfaceprocesses including the surface roughness, air-sea energy and momentumexchanges, wave breaking, and whitecap coverage. For more than six decades, thecmDm wave components are generally considered to be in the equilibrium range,and its spectral function has a constant slope: -5 or -4 in the 1D frequencyspectrum, and -3 or -2.5 in the 1D wavenumber spectrum. Some variations of theequilibrium spectrum models include varying the frequency spectral slope from 4to 5 at some multiple of the spectral peak frequency, or incorporating athreshold velocity in the reference wind speed. Extensive efforts are thendevoted to quantifying the spectral coefficient of the equilibrium spectrumfunction. The observed wind wave spectral slopes in the ocean environment,however, are rarely constant. The variable spectral slope is indicative of thenonequilibrium nature of surface wind waves in the field. As a result the waveproperties in field observations are significantly different from thoseinferred from assuming a constant spectral slope. From signal-to-noiseconsideration the surface slope measurements are much more sensitive than theelevation data for the study of cmDm waves. Recently, several large datasets oflow-pass-filtered mean square slope (LPMSS) have been reported in support ofthe Global Navigation Satellite System Reflectometry (GNSSR) tropical cyclonewind sensing effort. Combining the LPMSS observations with a spectrum modelthat accommodates a variable spectral slope, this paper seeks to quantify theconnection between the variable spectral slope and the spectral properties ofcmDm waves.

Variable Spectral Slope and Nonequilibrium Surface Wave Spectrum