The Effect of Latitude on the Sea Breeze

Abstract

Long-term (five-day) integrations of a nonlinear numerical model of the sea breeze at the equator, 20°N, 30°N and 45°N indicate the importance of latitude on the sea breeze circulation. During the hours of strong heating when friction is largest and the static stability is smallest, a local sea-breeze frontal circulation develops in a similar way at all four latitudes. Evaluation of the terms in the circulation theorem indicates the dominance of the solenoid term (horizontal pressure gradient force) associated with the strong temperature contrast during this period. During the rest of the period, however, the pressure gradient and frictional forces weaken, the static stability increases, and the Coriolis force is dominant (except at the equator). Therefore, quite different circulations evolve at the different latitudes. At the equator, the absence of the Coriolis force results in a sea breeze at all times. At the other latitudes, the Coriolis force is responsible for producing the large-scale land breeze. At 20°N, the slower rotation of the horizontal wind after sunset produces a large-scale land breeze that persists until several hours after sunrise. At 30°N, the inertial effects produce a maximum land breeze at about sunrise, and the land breeze is strongest at this latitude. At 45°, the rotational rate of the horizontal wind after sunset is faster, so that the maximum land breeze occurs several hours before sunrise. These results indicate that the Coriolis force may be more important than the reversal of horizontal temperature gradient from day to night in producing large-scale land-scale land breeze away from the equator. The results pertaining to the large-scale circulation are in general agreement with Rotunno's linear theory, which predicts a fundamentally different behavior of the sea-breeze circulation depending upon whether the Coriolis parameter is greater or less than the frequency of the diurnal heating cycle.