Vertical Circulation Revealed by Diurnal Heating of the Upper Ocean in Late Winter. Part II: Modeling

Abstract

A heat budget for observations at current meters in the mixing layer beneath a freely drifting spar buoy showed that the buoy must be in a convergence zone, where transport of warm water downwards enhances the diurnal heating effect. The convergence zone is probably associated with Langmuir circulations due to the strong, steady wind experienced before and during the 6-day deployment. This paper describes a two-dimensional numerical model of a Langmuir cell imposed on a mixed layer. The processes of advection and mixing occure Separately at each time step, after surface heat fluxes have been absorbed. Since momentum is not allowed to mix, we consider the evolution of the temperature field when a diurnal heating cycle is imposed, and determine the influence of the imposed circulation on the heat budget of the mixing layer. To obtain the amplitude and phase observed in the diurnal heating signal, a vertical velocity of 1 cm s?1 is required in the model.