Evidence for atmosphere-ocean meridional energy transport compensation in the past decades

We present evidence of compensation between the atmosphere and ocean's meridional energy transport variations, also known as Bjerknes compensation. Motivated by previous studies with mostly numerical climate models, we analyze compensation using a range of atmosphere and ocean reanalysis datasets. We show that Bjerknes compensation is present at almost all latitudes from 40 degrees North to 70 degrees North in the Northern Hemisphere from interannual to decadal time scales. In contrast to results from some numerical climate models, which attribute the compensation to variations of eddy energy transports in the atmosphere in response to changes of ocean heat transport and sea ice at multi-decadal time scales, we find a response of the zonal mean of poleward energy transport to ocean heat transport variability that leads to compensation. This is apparent in a meridional shift of the Ferrel Cell at midlatitudes at decadal time scales in winter. This shift in the cell itself is driven by changes in the eddy momentum flux and related baroclinicity. The oceanic response to atmospheric heat transport variations associated by the shift is primarily wind driven. In summer, there is hardly compensation and the proposed mechanism is not at work. Interestingly, these results are robust among all reanalysis datasets and can provide a benchmark for climate modelling studies.