On the rotation rate of the direction of sea and land breezes.

Abstract

Attention is drawn to the observational fact that the rate of turning of the direction of sea and land breezes is far from uniform over the diurnal cycle. A theoretical analysis of the problem is then undertaken for a two-dimensional sea and land breeze model. It is shown that the rate of local turAing equals the sum of three principal terms. The first term is -kf (f Coriolis parameter, k vertical unit vector), a term known from previous theoretical work; the second is the cross product of the horizontal mesoscale pressure gradient (approximately equivalent to the diurnal heating/cooling of the land relative to the sea) and the velocity of the breezes; the third involves the cross product of the horizontal large-scale pressure gradient, assumed not be affected by the diurnal heating, and the aforementioned velocity. All three terms represent rotation about the vertical but, while the first term is a constant, the other two are variable both in magnitude and sign. These two variable terms modulate the rate of turning in an important manner. Finally, the theoretical predictions are compared with observations and special situations are studied. (A)