On Dynamical Processes of Sea- and Land-Breeze Circulation

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Abstract
Response of a stably stratified Boussinesq fluid to differential heating with periodic time variation is investigated with linearized vorticity and thermodynamic equations. By introducing a suitable scaling, it is shown that the flow structures are controlled by a single non-dimensional parameter defined as Ω=ω*/N2/3(υ/l2)1/3 where ω* is the frequency of the thermal forcing, N is the buoyancy frequency, υ is the diffusion coefficient for heat and momentum and l is the horizontal scale of the heating (cooling) area. Internal gravity waves, conduction waves (propagating temperature perturbations governed by the equation of thermal conduction) and a steady heat island convection are regarded as basic physical phenomena contained in disturbances. When Ω is smaller than 1.3, the flow structures are not sensitive to Ω. They are essentially the same as that of the steady heat island convection. When Ω is greater than 1.3, horizontal and vertical scales of the disturbance are mainly controlled by the internal gravity waves and the conduction waves, respectively. SinceΩ is near 1.3 in the atmosphere, importance of the three basic physical phenomena is expected to be same in the sea- and land-breeze circulation observed in the atmosphere. By comparing these results with those of a numerical experiment and observational data at Osaka-city, non-linear effects near the sea-breeze front are discussed.

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