Covariability of SST and surface heat fluxes in reanalyses and CMIP3 climate models

The generation and dissipation of SST anomalies is modulated by the covariability of SST and surface heat fluxes. The heat fluxes, including the net flux and its radiative and turbulent components, and their connection to SST are investigated in the NCEP-NCAR and ERA-40 reanalyses and in the CMIP3 multi-model climate simulations. Simultaneous covariance patterns between SST and heat fluxes differ considerably between NCEP and ERA-40 reanalyses in the northern Pacific and Atlantic mid-latitudes. In those regions, the downward heat fluxes are negatively correlated with the SST anomalies in the NCEP reanalysis, while they are positively correlated with the SST anomalies in the case of ERA-40. The disparity is partially attributed to the different treatments of the air-sea interface in the two reanalyses. The covariance of temperature and heat flux differs substantially among the CMIP3 climate models but is generally small in the ensemble mean. Lagged covariances, by contrast, are broadly similar in the two reanalyses and among models, suggesting that heat flux feedbacks are comparable. Heat flux feedback is determined from the lagged cross-covariances together with the auto-covariance of SST. It is negative and is dominated by the turbulent component. Strongest feedbacks are found at mid-latitudes in both hemispheres, with largest values occurring in the western and central portions of the oceans with extensions to higher latitudes. The latter are also areas with high model-to-model variation.