THE UPPER-OCEAN RESPONSE TO SURFACE HEATING

Moored observations of atmospheric variables and upper-ocean temperatu res from the Long-Term Upper-Ocean Study (LOTUS) and the Frontal Air-S ea Interaction Experiment (FASINEX) are used to examine the upper-ocea n response to surface heating. FASINEX took place between January and June 1986 at 27 degrees N, 70 degrees W while LOTUS took place between May and October 1982 at 34 degrees N, 70 degrees W. The frequency-dom ain transfer function between rate of change of heat and the net surfa ce heat flux is consistent with a one-dimensional heat balance between heating and convergence of vertical turbulent heat flux at timescales longer than the inertial. The observations satisfy the vertically int egrated one-dimensional heat equation and indicate that the response t o surface heating has been successfully isolated. Within the internal waveband, upward phase propagation in the response is inconsistent wit h a one-dimensional balance and the vertically integrated heat balance fails. The internal waveband response is explained as a balance betwe en rate of change of heat, mixing, and vertical advection. A simple mo del, which admits internal waves forced by an oscillatory surface buoy ancy flux, illustrates the competition between these three terms. Stra tification modulates the depth to which surface heating is mixed. The estimated eddy diffusivity may be considered a linear function of freq uency where the scaling constant reflects the mixed layer depth.