Presenter: Paige Martin (Lamont-Doherty Earth Observatory/Australian National University)

Description:
The ocean and the atmosphere are distinct fluids whose dynamics act at preferred time scales. Exactly how the two fluids interact across timescales and the primary mechanisms responsible for air-sea coupling remain an outstanding question. In this work, air-sea interaction is diagnosed via ocean surface temperature variance. Terms in the temperature variance budget are computed from daily output of the Community Earth System Model’s ocean component. Two model resolutions are compared – a high-resolution (0.1 degree) ocean that resolves eddies and a low-resolution (1 degree) ocean that is not eddy-resolving. Horizontal advection of temperature, surface heat fluxes, and diffusion are computed explicitly, and an inferred residual accounts for vertical advection and vertical mixing. With specific interest in organizing the drivers of variance by timescale, all computations are carried out in the frequency domain. In the high-resolution model, horizontal advection is the primary global driver of variance at all timescales in this study (1 day - 10 years), with the exception of the seasonal cycle which is dominated by surface heat fluxes. The spatial patterns of both terms indicate that the western boundary currents are the dominant regions of ocean temperature variance across nearly all timescales. In the low-resolution model without resolved eddies, the surface heat fluxes are shown to be the main driver of variance through subannual scales, largely due to enhanced equatorial dynamics. These results suggest that the ocean mesoscales play a major role in driving surface temperature variance at timescales from daily to interannual, and add to a growing body of literature indicating that resolving eddies in global climate models is essential to accurately capture climate variability.