Different Behaviours of the Ross and Weddell Seas Surface Heat Fluxes in the Period 1972–2015

Abstract

Operational analyses and re-analyses, provided by ECMWF for the period 1972–2015, were used to investigate the behaviour of the surface heat fluxes between ocean and atmosphere, estimated via empirical formulae, over the Ross and Weddell Seas. The presence and thickness of sea ice cover, which strongly affects ocean-atmosphere interactions, was estimated through Special Sensor Microwave Imager and Special Sensor Microwave Imager Sounder brightness temperatures. Because of the lack of ice information before 1992, daily averaged ice and snow thickness obtained from the 1992–2012 dataset has been used as a ‘climatological year’ for the 1972–2015 period. The heat loss in the Ross Sea reached its maximum in 2008 (−98 W∙m−2) and its minimum (−58 W∙m−2) in 1980, while in the Weddell Sea, it ranged between −65 W∙m−2 (1999) and −99 W∙m−2 (2015). Results showed that the surface heat fluxes behaviour in the two seas moved from opposite to synchronous during the study period. The wavelet analysis was applied to evaluate if this result might be linked to the signature of global climate variability expressed by El Niño Southern Oscillation (ENSO) and Southern Annular Mode (SAM). The synchronous behaviour of the surface heat fluxes in the Ross and Weddell seas, observed since 2001, coincides with a change in the energy peak associated to the time scale of the SAM variability, which moved from 32 to 64 months during 1990s. This change generates a common energy peak for the SAM and ENSO with a lagged in phase relationship between the signals, possibly influencing the behaviour of the surface heat fluxes.