National Oceanic and
Atmospheric Administration
United States Department of Commerce


FY 2010

The annual range of southern hemisphere SST; Comparison with surface heating and possible reasons for the high-latitude falloff

Chiodi, A.M., and D.E. Harrison

J. Climate, 23, 1994–2009, doi: 10.1175/2009JCLI3154.1 (2010)

Globally, the seasonal cycle is the largest single component of observed sea surface temperature (SST) variability, yet it is still not fully understood. We here examine the degree to which the structure of the seasonal cycle of Southern Hemisphere SST can be explained by our present understanding of surface fluxes and upper ocean physics. It has long been known that the annual range of Southern Hemisphere SST is largest in the mid-latitudes, despite the fact that the annual range of net surface heat flux peaks well poleward of the SST peak. The reasons for this discrepancy (“fall off of annual range of SST”) are determined here through analysis of net surface heat flux estimates, observed SST and mixed layer depth data, and results from experiments using two different 1-dimensional ocean models. Results show that, (i) the classical explanations for the structure of the annual range of SST in the Southern Hemisphere are incomplete, (ii) current estimates of surface heat flux and mixed layer depth can be used to accurately reproduce the observed annual range of SST, and (iii) the prognostic mixed layer models used here often fail to adequately reproduce the seasonal cycle at higher latitudes, despite performing remarkably well in other regions. This suggests more work is necessary to understand the changes of upper ocean dynamics that occur with latitude.

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