A possible effect of ENSO and SAM over surface heat budgets in the Ross and Weddell Seas

Operational analyses and re-analyses, provided by ECMWF for the period 1958-2010, were used to investigate the role of atmospheric forcing in the Ross and Weddell Seas. State variables have been used to estimate the surface heat fluxes via empirical formulae. Interactions between atmosphere and ocean are strongly influenced by the presence/absence of the ice cover. For this reason, SSM/I data were used to detect ice cover for the available period. Moreover a new algorithm was implemented to estimate the sea ice thickness from SSM/I brightness temperature in the study areas. The heat loss, in the Ross Sea, reaches its maximum in 2008 (-98 Wm-2) and its minimum (-65 Wm-2) in 1972. In the Weddell Sea it ranges between -67 Wm-2 (1990) and -96 Wm-2 (2008). The studied areas show synchronous or opposite variations depending on the period. Explanation of this behaviour may be linked to the signature of global climate variability expressed by El Niño Southern Oscillation (ENSO) and Southern Annular Mode (SAM) through their indices respectively SOI and SAMi. In order to detect any relationship the wavelet analysis was used. Main periods of variability of the two indices were evaluated. A change in the variability scale of the SAM was detected from 1993 to 2004, while other variability scales, from 1 year to about 5 years, are more stable for both phenomena. Successively, by means of cross-wavelet and wavelet coherence analyses, a different influence of the atmospheric phenomena over the seas was found. In particular short variability scales up to 2 years are usually more significant, and anti correlated, over the Ross Sea area. On the other hand longer variability periods of the indices seem to be more connected to the Weddell Sea surface fluxes with a change of the correlation sign in coincidence with the change observed in the SAMi typical variation scales.