Pezzi, L. P., M. F. L. Quadro, J. Lorenzzetti, A. Miller, E. B. Rosa, L. N. Lima, U. A. Sutil, R. de Camargo and R B. Souza, 2018:

Do oceanic SACZ episodes modulate SST via upper-ocean dynamics and thermodynamics?

Journal of Climate, sub judice.

Abstract. The South Atlantic Convergence Zone (SACZ) is an atmospheric phenomenon occurring in the austral summer and is characterized by the persistence of a northwest-southeast-oriented cloud band. Its presence causes sea surface cooling. Here we investigate the interaction processes between atmosphere and Southwestern South Atlantic (SWA) concerning air-sea fluxes during intense episodes of oceanic SACZ. We are interested in dynamic and thermodynamic coupling mechanisms and how they are balanced during these episodes. Using regional ocean and atmosphere coupled models we show that during oceanic SACZ episodes there is an ocean surface cooling. A heat budget balance is made over the ocean mixed layer, whose variable depth is estimated at each model´s grid point. The surface atmospheric circulation and the presence of cloud cover band over SWA promote the sea surface cooling via dynamic and thermodynamic mechanisms, which are same order of magnitude. SST decreases on regions underneath oceanic SACZ positions, near the Southeast Brazilian coast, at South Brazil Bight (SBB) and offshore. Also another singular feature found in this study is the presence of an atmospheric cyclonic vortex at both, surface and above at 850 hPa, near 24°S and 45°W. This atmospheric circulation is established by oceanic SACZ and provokes this sea surface temperature (SST) decrease to the southwestward from where SACZ is positioned. This shows that the dynamical effect of the atmospheric surface circulation associated with the oceanic SACZ, are not restricted to the region well underneath it. The presence of cooled sea surface waters underneath this cyclonic vortex seems to be produced by the induced divergent Ekman transport.

Preprint (pdf)