[1] This study analyzes and discusses data taken from oceanic and atmospheric measurements performed simultaneously at the Brazil-Malvinas Confluence (BMC) region in the southwestern Atlantic Ocean. This area is one of the most dynamical frontal regions of the world ocean. Data were collected during four research cruises in the region once a year in consecutive years between 2004 and 2007. Very few studies have addressed the importance of studying the air-sea coupling at the BMC region. Lateral temperature gradients at the study region were as high as 0.3°C km À1 at the surface and subsurface. In the oceanic boundary layer, the vertical temperature gradient reached 0.08°C m À1 at 500 m depth. Our results show that the marine atmospheric boundary layer (MABL) at the BMC region is modulated by the strong sea surface temperature (SST) gradients present at the sea surface. The mean MABL structure is thicker over the warmside of the BMC where Brazil Current (BC) waters predominate. The opposite occurs over the coldside of the confluence where waters from the Malvinas (Falkland) Current (MC) are found. The warmside of the confluence presented systematically higher MABL top height compared to the coldside. This type of modulation at the synoptic scale is consistent to what happens in other frontal regions of the world ocean, where the MABL adjusts itself to modifications along the SST gradients. Over warm waters at the BMC region, the MABL static instability and turbulence were increased while winds at the lower portion of the MABL were strong. Over the coldside of the BC/MC front an opposite behavior is found: the MABL is thinner and more stable. Our results suggest that the sea-level pressure (SLP) was also modulated locally, together with static stability vertical mixing mechanism, by the surface condition during all cruises. SST gradients at the BMC region modulate the synoptic atmospheric pressure gradient. Postfrontal and prefrontal conditions produce opposite thermal advections in the MABL that lead to different pressure intensification patterns across the confluence.

A new climatology of South Atlantic cyclones is produced to provide new insights into the conditions leading to genesis in different regions of the domain. Cyclones are identified and tracked based on the relative vorticity at 850 hPa computed from the NCEP-CFSR winds. The characteristics of the cyclones are obtained by diagnostic variables sampled within a radial distance from the cyclone centers to produce the spatial distribution of cyclone properties at the time of genesis. Also, cyclone centered composites are used to analyze the cyclone structure and evolution during their genesis. There are four main cyclogenesis regions in the South Atlantic Ocean: the Southern Brazilian coast (SE-BR, 30 • S), over the continent near the La Plata river discharge region (LA PLATA, 35 • S), the southeastern coast of Argentina (ARG, 40 • S-55 • S) and the Southeastern Atlantic (SE-SAO, centered at 45 • S and 10 • W). We found that cyclogenesis northward of 35 • S occurs mainly due to low-level forcing associated with moisture transport in the summer, and is associated with upper-level forcing in the winter due to a strong baroclinic environment. Southward of 35 • S, cyclones develop in a high baroclinic environment throughout the year with only a small influence from moist processes. The cyclone composites reveal that SE-BR and SE-SAO cyclones are associated with secondary development, the LA PLATA cyclones development is influenced by an orographic low in their early stages, and ARG cyclones are

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[1] The influence of the Brazil-Malvinas Confluence (BMC) region on the marine atmospheric boundary layer (MABL) is investigated through in situ data analysis of five different cruises (2004 to 2008) and numerical experiments with a regional atmospheric model. Two different groups of numerical experiments were performed in order to evaluate the relevance of static stability and hydrostatic balance physical mechanisms for the MABL instability. The first group used monthly climatological sea surface temperature (SST) as bottom boundary condition while the second used daily updated Advanced Microwave Scanning Radiometer-EOS SST data together with radiosondes and surface data assimilation. A reasonable agreement between numerical results and QuikSCAT wind data was observed through correlation coefficients and mean square error values. In terms of the horizontal structure of the MABL, stronger winds were found over the warm side of the BMC region as well as over the thermal front itself, which supports the coexistence of both modulation mechanisms. The analyzed patterns of surface atmospheric thermal advection showed a clear interaction between the synoptic and regional scales. The signature of the oceanic thermal front (almost meridionally oriented) on the air temperature at 2 m makes the temperature advection strongly determined by the zonal component of the wind. The analysis of momentum budget terms did not show a clear and reasonable explanation of the existence or predominance of the modulation mechanisms, and it also suggested the relevance of other effects, such as the idea based on unbalanced Coriolis force and turbulence/friction effects.Citation: de Camargo, R., E. Todesco, L. P. Pezzi, and R. B. de Souza (2013), Modulation mechanisms of marine atmospheric boundary layer at the Brazil-Malvinas Confluence region,

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