Diurnal Cycling: Observations and Models of the Upper Ocean Response to Diurnal Heating, Cooling, and Wind Mixing

摘要

A diurnal cycle occurs when solar heating warms and stabilizes the upper ocean. This limits downward penetration of turbulent wind mixing so that air-sea fluxes of heat and momentum are surface trapped during midday. The central problem is to learn how the trapping depth DT (mean depth value of the diurnal temperature and velocity response) is set by the competing effects of wind mixing and surface heating. In this data set the diurnal range of surface temperature Ts was observed to vary from 0.05 < Ts < 0.4 C, with most of the day-to-day variability attributable to variations of wind stress. Wind mixing causes a pronounced asymmetry of the Ts response by limiting the warming phase to only about half of the period that the surface heat flux is positive. The associated wind-driven current, the diurnal jet, accelerates downwind during the morning and midday. It is turned into the wind by the Coriolis force during early evening and is often erased by the following morning. (Reprints).