Pressure Gradients and Winds in Cook Strait

Abstract

Wind channeling effects in a major strait have been studied using pressure data from seven meteorological stations in and around Cook Strait, New Zealand. The data were analyzed using pairs of stations to obtain pressure differences and groups of three stations to give vector gradients. Wind data from a hill site in the channel have been used as a measure of the wind in Cook Strait. Wind directions have a range of orientations relative to the pressure gradient but are almost parallel to it for a substantial amount of the time, rather than approximately perpendicular to it as is the case in the open ocean. The balance of terms in the equation of motion perpendicular to the wind direction indicates that flow curvature is important in Cook Strait. In the balance of terms along the wind direction, the acceleration term is usually larger than the friction term in the entrance regions. With southerly wind directions, the pressure gradient direction in the southern entrance zone to the strait has an unusual relation to the wind direction and varies over a wide range. This latter feature is attributed to the reactions set up between the mountains and the varying orientations of the incident airstream.