A Numerical Study of Nocturnal Sea Breezes: Prefrontal Gravity Waves in the Compensating Flow and Inland Penetration of the Sea-Breeze Cutoff Vortex

Abstract

It is demonstrated in this numerical study that prefrontal perturbations may be triggered by a penetrating sea-breeze head into an existing nocturnal temperature inversion. The perturbations consist of the lower-layer wavelike perturbation and the upper-wave motion, both of which are manifested as rotor streaming. However, these prefrontal gravity waves take the form of the weak transient waves of a depression trapped in the ambient compensating flow field. The sea-breeze head dissipates as it penetrates inland into the nocturnal temperature inversion. At midnight, a horizontal vortex is completely detached from the feeder flow of the sea breeze. This isolated horizontal vortex is identified as the sea-breeze cutoff vortex. It is shown that the sea-breeze cutoff vortex may be evolved from a dissipating sea-breeze head. After the sea-breeze cutoff vortex is formed, it propagates farther inland as an isolated wave-type disturbance. Examination of the force balance suggests that the inertia and radiative energy loss are dominant in the processes of the sea-breeze cutoff vortex.