Understanding the annual cycle in global steric height

Abstract

Steric variability in the ocean includes diabatic changes in the surface layer due to air-sea buoyancy fluxes and adiabatic changes due to advection, which are dominant in the subsurface ocean. Here the annual signal in subsurface steric height (η′below 200 db) is computed on a global scale using temperature and salinity profiles from Argo floats. The zonal average of Δη′ over a season (e.g., ηMarch′-ηDecember′) is compared to the wind-forced vertical advection contribution (Δηw′) both in the global ocean and in different basins. The results show agreement that extends beyond the tropics. The estimate of Δηw′ is based on the Ekman pumping and assumes that the seasonal vertical velocity is constant over the depth range of interest. This assumption is consistent with annual isopycnal displacements inferred from Argo profiles. The contribution of horizontal advection to Δη′is significant in some regions and consistent with differences between Δη′ and Δηw′. Key Points Annual dynamical subsurface ocean variability is described globally The oceanic annual response is in balance with the wind-forcing The vertical structure of annual variability is slowly-varying. © 2013. American Geophysical Union. All Rights Reserved.