The Influence of Fetch on Whitecap Coverage as Deduced from the Alte Weser Lightstation Observer’s Log

Some 1500 visual observations of whitecapping as logged at the Alte Weser Light-station offshore from Bremerhaven in the period from September 1970 to May 1972 were made available by Dr H. Gienapp of the Deutsches Hydrographisches Institut. Each observation included estimates of the fraction of the waves with whitecaps (F), the average width of these white- caps (B), and the wavelength of the swell (L). The mean whitecap coverage (W) for each observation was estimated using Eq. 1, and each observation was $${\rm{W = FB}}{{\rm{L}}^{ - 1}}$$ assigned a fetch category: infinite (azimuth 308°- 340°), 131 observations; open North Sea (256°- 308°, 340°-358°), 235 observations; limited (358°- 053°, 247°-256°), 250 observations; or extreme limited (053°-247°), 831 observations.