Climatea Journal Club


Tuesday, November 14, 2017, 3:00pm to 4:00pm


Seminar Room, 429

Speaker: Xioating Yang

Xiaoting is going to lead a discussion on paper: “Vertical heat flux in the ocean: Estimates from observations and from a coupled general circulation model”. Here is her thoughts about the paper:

"The vertical heat transport of the ocean involves the terms associated with the time-mean circulation, eddy-induced motion, convection and small scale turbulent dissipation. In a changing climate, a small imbalance between these terms leads to a net heat uptake by the ocean, which accounts for more than 90 percent of the additional warming of the Earth and contributes to the global sea level budget through thermal expansion. The dominant balance in ocean vertical heat transport has been under debate for years. The paradigmatic diapycnal advective-diffusive balance between downward diffusion of heat and upwelling of cold abyssal water, is found to be in conflict with GCM and data assimilation analysis which indicates that when globally averaged, the downward heat transport associated with the mean circulation is largely balanced by the upward eddy-induced transport, whose residual is further balanced by diffusion, making the vertical heat transport by mean circulation a key component in this budget. This paper makes a novel attempt to diagnose vertical heat flux associated with the time-mean circulation from observational data sets, with the vertical velocity obtained by geostrophic vorticity balance, given an estimate of the absolute geostrophic velocity. Comparison with a non-eddy-permitting coupled atmosphere and ocean general circulation model shows reasonable agreement in the latitudinal distribution of vertical heat flux below 250 meters. This means that the most salient characteristics in the vertical heat transport can be inferred from observations by using geostrophic vorticity balance. The vertical heat flux is dominated by downward contribution from the Southern hemisphere, especially in the Southern Ocean. This downward heat flux is driven by Ekman vertical velocity which induces upward motion of Circumpolar Deep Water, which is cold relative to horizontal average at a given depth. “

cummins_et_al-2016-journal_of_geophysical_research_oceans.pdf8.58 MB