OS23C-01
A Numerical Study of the Impact of Changes in Antarctic Sea-Ice on the Brazil Malvinas Confluence Region
The Brazil Malvinas Confluence (BMC) region , where the warm and salty southward flowing Brazil current encounters the cold and less saline northward flowing Malvinas current, is considered one of the most energetic of the world ocean. This study investigates the sensitivity of the BMC, considered here from 38-44°S, to changes in extreme Antarctic sea-ice concentration using the NCAR-CCSM3 coupled model. Three simulations with 150 years for sea ice concentration (SIC) with maximum (MAX), minimum (MIN) and control climatologies (CTRL) from satellite-derived data were analyzed to determine the response of the ocean circulation to sea-ice extent forcing. The SST values for the SIC MIN experiment exhibit temperature 1°C warmer than the SST for the SIC CTRL experiment results around 42°S. However, the SST results for SIC CTRL shows temperature of 1.5°C warmer than the values for the results obtained using SIC MAX for the same location. It is also seen in the mean temperature of the upper 500m also at 42°S that the higher temperatures in the SIC MIN experiment are associated with a southward displacement of the BMC. Analyses of the barotropic transport shows an intensification of 5Sv in the SIC MAX western boundary circulation at 44°S relative to the SIC CTRL results. Differences in the transport for, SIC MIN relative to the control experiment is only 2Sv. The transport intensification observed is directly correlated with the intensification of the winds in the SIC MAX. Correlations between the wind stress curl and the barotropic transport, for the SIC MAX, MIN and CTRL in the BMC region is -0.68, -0.83 and -0.85, respectively.
OS23C-02
Seasonal Variability Of The Meridional Transport Along The Northeastern Brazilian Edge
The dynamics of the southern band of the South Equatorial Current (sSEC) near to Brazilian shelf is investigated using recent field observations and a regional numerical modelling approach. Ocean measurements were obtained from five moorings deployed by German CLIVAR (Climate Variability and Predictability Program) cruises (March 2000-May 2003) along a crossshore line at 11° S. The Regional Ocean Model (ROMS) is used to simulate the circulation and thermohaline structures within the ocean area comprised between 5° S-25° S and 20° W-47° W. This integration domain was covered by an isotropic 1/12° horizontal grid and 40 terrain-following layers. The numerical results confirm a seasonal migration of the core sSEC divergence along the Brazilian edge, as well as its depth dependence with a maximum northward shift in July at 180 m layer, while a maximum southward displacement occurs in November at this same depth. This intrannual variability coincides with the North Brazil Undercurrent (NBUC) seasonality at 11° S such as moorings measurements, Empirical Orthogonal Function (EOF) and numerical results show a minimum NBUC strength during November (field data = 14.7 Sv; model = 19.1 Sv), a maximum northward transport in July (field data = 29.8 Sv; model = 29.8 Sv), and a quasi-semestral periodicity of the NBUC core (EOF1 = 97%). Furthermore the North Atlantic Deep Water (NADW) variability observed at the deeper colder layers (and reproduced by the model) seems to be linked to upstream instability from eddies passage in the Deep Western Boundary Current (DWBC). The variability is decomposed into two separate modes accounting for 69% and 25% of the total variance in the lower and upper NADW layers, respectively. Numerical results and EOF indicated a cycle of 60-70 days (EOF1 = 69%) for the core of the DWBC at 1900 m depth. According to simulations the upstream DWBC flow is reinforced between 7° S- 10° S during austral winter, thus enhancing anticyclonic eddies generation along 10° S-17° S, whereas upstream DWBC flow is reduced during the austral summer, when downstream eddies is less pronounced. A counterflow offshore from NBUC was identified in the numerical results and EOF analysis at 500 m depth (EOF2 = 25%). The EOF for (T-V) fields exhibit temperature strongly coupled to the velocity current at the core of the DWBC for the first year of data, which reveals that this two fields are synchronized each two months.
OS23C-03
The oceanic response due to atmospheric forces in global scale - an observational and numerical approach with emphasis in the South Hemisphere
The oceanic and atmospheric intraseasonal variability has been studied in global scale with emphasis on South Hemisphere through a general descriptive analysis. The possible connections of both systems (ocean and atmosphere) have been investigated. Sea surface temperature (SST), meteorological wind fields, short wave radiation and latent and sensible heat fluxes data have been statistically treated to identify and analyze the intraseasonal oscillations characteristics of the interface ocean-atmosphere. Through these determinations the ocean model response of the Princeton Ocean Model (POM) is being evaluated in global scale in the intraseasonal band. The oceanic model has been forced using superposition of wind and heat flux averages (so the surface currents and the termohaline circulation are maintained) with general characteristics of the intraseasonal anomalies. These anomalies were determined through statistic data treatment in specific periods in order to compare climatological situations with those ones forced with the presence of intraseasonal perturbations that propagate over the ocean.
OS23C-04
Intraseasonal Variability Of Tropical And South Atlantic - Observation And Modeling
Intraseasonal variability on the Tropical and South Atlantic has been analyzed through the use of SST and surface wind data respectively from TMI and QuikScat satellite missions and also through numerical modeling on basin scale with Princeton Ocean Model. The intrinsic intraseasonal ocean variability and the correspondent co- variability with atmosphere were evaluated in terms of SST and surface wind anomaly fields and their cross wavelet transforms, both for observations and modeled results. Observations related to the tropical area revealed that: (i) the presence of intrinsic ocean intraseasonal variability (30-40 days) mainly from July to October associated to TIW activity with strong influence over surface winds, i.e., dominance of ocean over atmosphere in longer intraseasonal periods and (ii) atmospheric driven intraseasonal ocean variability from February to May with smaller intraseasonal periods. Besides, the extra-tropical areas with permanent strong temperature gradients (Brazil-Malvinas Confluence as well as Agulhas Current) presented a similar behavior, but not necessarily during the same months. In a general way, the numerical experiments with POM with 0.5 degree resolution could capture the intrinsic ocean behavior in both tropical and extra-tropical regions, which means that the physical mechanism has been well represented by the model.