Notes from “Eddy Advective and Diffusive Transports of Heat and Salt in the Southern Ocean” by Lee et al. (2007)

• In this paper, the authors review briefly how to diagnose the mean, eddy advective and eddy diffusive transport of a tracer (Section 2).

• “To predict the direction of eddy advective heat transport, we use the eddy transport streamfunction and mean temperature”

• I do not understand this issue:

  Although the direction of advective heat transport cannot be uniquely defined in each individual isopycnic layer, the vertically integrated eddy advective heat transport can because the vertical integral of eddy mass transport is nearly zero at each point (this is why we use V_eddy rather than V_bolus).

Maybe I understand now. Using their Fig. 1 and the eddy advection of heat, the lower layer is defined as “cold” because we know it is colder than the above layer. If we do not know if the temperature is colder or warmer in the upper layer, then we cannot tell if the net eddy flux is poleward or equatorward. But this is true only if the temperature stays the same within the isopycnal layer. We can imagine that salt is important and the temperature increases equatorward, for instance, inside the layer. What happens in this case?

• Using scaling analysis, they come up with a rule of thumb to guess if the eddy advective and eddy diffusive flux are in the same direction depending on the relative slopes of the tracer contours and isopycnal surface (see their Fig. 8): if the tracer contours are steeper, then the two fluxes are in the same direction, and inversely.