Some observations of air flow over the sea

Abstract

Abstract Wind speeds were measured over the sea at five heights up to 8 m. Though the fetch was limited, the wind profiles obtained are considered representative of flow over the sea. The wind speed varies logarithmically with height when the temperature gradient is small. Assuming that laboratory laws of flow are applicable, values of the roughness parameter z 0 are deduced. It is found that z 0 increases from about 0·02 cm in a wind of 5 m/sec to 0·25 cm at 9 m/sec. The relationship between wind speed and z 0 however is not unique for the state of the surface is determined by other factors beside wind speed. In inversion conditions the wind‐speed distribution departs from the logarithmic form a few metres above the surface. The results obtained are compared with those of some other workers. Bi‐directional vanes were used to obtain gustiness measurements at the site. While the vertical gustiness is found to be of similar magnitude to that over land surfaces of comparable roughness, the cross‐wind gustiness appears to be greater over the sea.