Winds in the Strait of Gibraltar

Automated meteorological observations were made from October 1985 to September 1986 in the narrows of the Strait of Gibraltar. Additional surface and upper-air measurements were made in the Strait from May to July 1986. The main wind events in summer were mostly mesoscale levanters (winds from the east through the Strait), and a lesser number of synoptic-scale levanters and westerlies. During mesoscale levanters, the wind speed increased and the pressure decreased from Gibraltar downstream through the narrows as far as Tangier. A mesoscale low and the highest winds were found over the axis of the Strait, north of Tangier. High-velocity (20 m s(-1)) winds occurred only under 1-km height. The air-temperature profile became progressively warmer moving from Gibraltar towards Tangier. A weak air-temperature inversion decreased in height to the west of the narrows. Venturi flow as an explanation for the downstream increase of the low-level winds during a levanter is inconsistent with observations. A new model is proposed to explain the wind field associated with levanter winds in the Strait that includes some orographic blocking and low-level convergence into the narrows, some west-side divergence due to drag over water, and leeside heating that generates a leeside, mesoscale low pressure. The surface low accelerates the surface winds to their maximum strength well downstream of the narrows. A similar now regime has been observed recently in the sea-level channel between Hawaii and Maul.