THE ATMOSPHERIC FORCING AS A SOURCE FOR OCEAN MESOSCALE ACTIVITY

SIMIONATO, C. G.

Pretoria, Sudáfrica

Conferencia; 5th. International Conference on Southern Hemisphere Meteorology and Oceanography; 1997

AMS

            Orlanski and Polinski (1983) show that mesoscale atmospheric forcing can be an important source for ocean mesoscale variability. The Brazil-Malvinas Confluence is characterized a high variability over a wide range of spatial and temporal scales and its continental counterpart is one of the with highest cyclogenetic activity within the Southern Hemisphere, cyclones been generated in the Patagonic region and in eastern South America. This last cyclogenesis have a frequency of 8 to 10 high intensity events by year and many more of lower intensity; Patagonic cyclogenesis is usually even more frequent and intense. During these events winds can reach more than 35 knots, and the spatial scale of the storms is of several hundred of kilometers.               Due to the scale of these phenomena, to the fact that they are strongly influenced by the Cordillera de los Andes and to their explosive nature, their forecast through general circulation models is difficult, and it is improbable to observe them in their real magnitude in data derived from analysis. This data are usually used to force ocean models which, in turn, fail to reproduce the magnitude of the observed oceanic variability in the area.               Because of the cloud cover associated to these cyclones it is not possible to use satellite data to observe the situation in the ocean during these events, but an analysis of weekly analyzed satellite SST data for the region shows that in weeks when a cyclone passes over the Confluence area, a variation in the oceanic temperature of the order of up to more than 1°C is produced, suggesting that storms have an important and persistent effect on the mesoscale oceanic range.               The goal of this study is to show by means of a nested high resolution numerical model, that the atmospheric mesoscale activity can be an important source for oceanic mesoscale variability. A situation occurred on November 10-12, 1989 was chosen for being one of the most intense of the last decades and haven been reproduced with a high resolution atmospheric numerical model by Seluchi and Saulo (1996).               Model succeeded on representing qualitatively and quantitatively well the pattern of the perturbation observed  on data. An analysis of the results of this high resolution numerical simulation and a persistence  study will be discussed in the full paper.