2004 LOM Workshop

Tuesday 2:00 - 2:20 p.m.

Coupled Modes of variability in the South Atlantic. A comparison of model results with observations

Edmo Campos, Roberto DeAlmeida, Reindert Haarsma, Rainer Bleck and Carlos Lentini
Instituto Oceanografico da Universidade de Sao Paulo
edmo@io.usp.br

ABSTRACT

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Coupled modes of variability in the South Atlantic were investigated with the output of the MICOM-CCM3 ocean-atmosphere model, run at the Los Alamos National Laboratory. The main objective was to compare the model patterns of variability, from interannual to multidecadal time-scales, with results of similar analyses with the NCEP data set. Using EOFs and Maximum Covariance Analysis (MCA) between SST and MSLP with zero lag, we found dipolar modes of SST variability very similar to those reported in the scientific literature in recent years. Spectral analysis of the dipole-like mode of SST variability in the model output shows two significative time-scales: one at 2.5 years and the othr at 27 years. The interannual time-scale is correlated with the ENSO signal while the multidecadal variability seems to be related to the Atlantic Meridional Overturning Circulation. Similarly to a previous study with NCEP data, lead-lag MCA between anomalous SST and atmospheric variables, with the model output, indicate the existence of two modes of variability of the atmospheric South Atlantic Convergence Zone (SACZ). One of these modes is a result of remote forcing while the other is a local response to the oceanic forcing. The differences between the two analyses are due to the different climatological states of the data and the model output: there is an excessive southward displacement of the Austral Summer ITCZ in the model result.

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LOM Users' Workshop, February 9-11, 2004