Diathermal heat transport in a global ocean Model

• Published in: Journal of Physical Oceanography
• Main Authors: Holmes, RM, Zika, JD, England, MH
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: American Meteorological Society 2019
• Subjects: 14 Life Below Water; anzsrc-for: 0405 Oceanography; anzsrc-for: 0911 Maritime Engineering; Pacific; Sea ice
• Online Access: http://hdl.handle.net/1959.4/unsworks_73548; https://doi.org/10.1175/JPO-D-18-0098.1

The rate at which the ocean moves heat from the tropics toward the poles, and from the surface into the interior, depends on diabatic surface forcing and diffusive mixing. These diabatic processes can be isolated by analyzing heat transport in a temperature coordinate (the diathermal heat transport). This framework is applied to a global ocean sea ice model at two horizontal resolutions (1/48 and 1/108) to evaluate the partioning of the diathermal heat transport between different mixing processes and their spatial and seasonal structure. The diathermal heat transport peaks around 228C at 1.6 PW, similar to the peak meridional heat transport. Diffusive mixing transfers this heat from waters above 228C, where surface forcing warms the tropical ocean, to temperatures below 228C where midlatitude waters are cooled. In the control 1/48 simulation, half of the parameterized vertical mixing is achieved by background diffusion, to which sensitivity is explored. The remainder is associated with parameterizations for surface boundary layer, shear instability, and tidal mixing. Nearly half of the seasonal cycle in the peak vertical mixing heat flux is associated with shear instability in the tropical Pacific cold tongue, highlighting this region's global importance. The framework presented also allows for quantification of numerical mixing associated with the model's advection scheme. Numerical mixing has a substantial seasonal cycle and increases to compensate for reduced explicit vertical mixing. Finally, applied to Argo observations the diathermal framework reveals a heat content seasonal cycle consistent with the simulations. These results highlight the utility of the diathermal framework for understanding the role of diabatic processes in ocean circulation and climate.