Term: sea_surface_primary_swell_wave_from_direction_at_variance_spectral_density_maximum

Unit: degree

Unit ref: UAAA

AMIP:

GRIB:

The quantity with standard name sea_surface_primary_swell_wave_from_direction_at_variance_spectral_density_maximum is the direction from which the most energetic waves are coming in the primary swell wave component of a sea. Swell waves are waves on the ocean surface and are the low frequency portion of a bimodal wave frequency spectrum. The primary swell wave is the most energetic swell wave in the low frequency portion of a bimodal wave frequency spectrum. The spectral peak is the most energetic wave in the wave spectrum partition. The phrase "from_direction" is used in the construction X_from_direction and indicates the direction from which the velocity vector of X is coming. The direction is a bearing in the usual geographical sense, measured positive clockwise from due north. The wave directional spectrum can be written as a five dimensional function S(t,x,y,f,theta) where t is time, x and y are horizontal coordinates (such as longitude and latitude), f is frequency and theta is direction. S has the standard name sea_surface_wave_directional_variance_spectral_density. S can be integrated over direction to give S1= integral(S dtheta) and this quantity has the standard name sea_surface_wave_variance_spectral_density.