Diabatic upwelling in the Tropical Pacific: Seasonal and subseasonal variability

Part of this upwelling arises from water flowing along isotherms sloping up to the east, but it also includes water mass transformation and consequent diabatic (cross-isothermal) flow (w(ci)) that is a key element of surface-to-thermocline communication.

In this study we investigate the mean seasonal cycle and subseasonal variability of cross-isothermal flow in the cold tongue using heat budget output from a high-resolution forced ocean model. Diabatic upwelling is present throughout the year with surface-layer solar-penetration-driven diabatic upwelling strongest in boreal spring and vertical mixing in the thermocline dominating during the rest of the year. The former constitutes warming of the surface layer by solar radiation rather than exchange of thermal energy between water parcels.