EXCHANGE PROCESSES BETWEEN THE BAÍA DE TODOS OS SANTOS AND THE EASTERN BRAZILIAN SHELF: THE IMPACT OF DOWNSCALING FROM A 1/12 OCEAN FORECASTING SYSTEM TO A BAY/COASTAL REGIONAL SYSTEM Marta-Almeida M, Mauro Cirano, Lessa, GC, Aguiar, AL, Amorim FN International Coordination Workshop (ICW4) of the Coastal and Shelf Seas Task Team (COSS-TT)/ARCOM Pilot Workshop 31 August to 04 September 2015 Lisbon, Portugal
Introduction A very high-resolution modeling configuration for a multi corner domain was created for the estuary of Baía de Todos os Santos (BTS), Brazil, and adjacent coastal waters The grid is a result of a downscaling strategy from a REMO 1/36 x 1/36 regional grid that uses boundary and initial conditions from global HYCOM/NCODA (1/12 x 1/12 ) Baía de Todos os Santos and the adjacent shelf and oceanic region. The main geographic features and landmarks are depicted.
Regional Grids METAREA V METAREA V - Brazilian responsibility (WMO-IOC/JCOMM) for marine forecasts and warnings: E grid 1/36 o (289 x 409 grid points) 32 Sigma levels Winds and atmospheric fluxes from CFSR Tides from TPXO Rivers from Dai et al. (2009) Boundary and initial conditions from global HYCOM/NCODA
BC E 1/36 o grid The region has the narrowest shelf along the Brazilian continental margin (< 10 km) It is influenced by: Tides SEC The latitudinal excursion of the South Equatorial Current bifurcation, which impacts the WBC system and associated meso-scale activity Seasonal winds The passage of frontal systems Local topography (Salvador Canyon) (see CSR, Amorim et al., 2011, 2012, 2013) The shelf break is represented by the 70 m isobath (bold black line), followed by the 200 m, 500 m, 1000 m, 2000 m, 3000 m and 4000 m.
E 1/36 o grid Summer (January) Winter (July) Seasonality of the mean surface circulation. Extracted from Amorim et al. (2013).
E 1/36 o grid IS SB BC wind January January NBUC Inner shelf Shelf break July Mean alongshore currents at 14 S show the BC (top 150 m) and NBUC (below) during January and a reverse of the upper circulation during July Time series of the currents (surface in black) show that the system is more baroclinic during summer and influenced by winds and WBC dynamics at the shelf-break
The high resolution grid Grid design A multi-corner grid was adopted to eliminate shadow regions Grid cell varying from 300 m (bay) to 1200 m (coastal region)
Bathymetry: gray (parent model grid), red (original), black (high resolution grid). The isobaths are 70 m, 1000 m, 2000 m and 3000 m The high resolution grid Grid design A multi-corner grid was adopted to eliminate shadow region Grid cell varying from 300 m (bay) to 1200 m (coastal region) Downscaling strategy: L1 is the bathymetry convergence layer L2 is the nudging convergence layer
The high resolution grid Results Sea Level Evaluation of the results based on sealevel, currents and the thermohaline structure Sea-level: Semi-diurnal components explain 98.5% of the variability
The high resolution grid Results Sea Level The sub-tidal seasonal and anomaly signals measured at the GLOSS station show high correlation, indicating the model configuration is dealing with high skills with forcings other than tidal (atmospheric surface forcing and lateral open boundaries forcing from the parent model) A multi-corner grid was adopted to eliminate shadow region Grid cell varying from 300 m (bay to 1200 m ) R = 0.70 R = 0.86
The high resolution grid Results Depth averaged currents The M 2 tidal ellipses compare well with observations where the modeled bathymetry is close to the real bathymetry At T2, the scaled ellipse (red) compares much better with observations
The high resolution grid Results River Discharge The area of study is inserted in a region where the monthly climatological river discharges are relatively small (total inflow < 200 m 3 /s). Climatological rivers discharges used in the model simulation. The dashed line represents all the rivers with the exception of Paraguaçu river.
The high resolution grid Results River Discharge While a monthly climatology was initially used, care has to be take for rivers that have their discharge regulated by dams, which is the case of the largest individual river inflow in the region Monthly mean inflow (blue) and discharge (red) of the Pedra do Cavalo dam at the Paraguaçu river. The bottom panels illustrate the time series of January and May averaged discharge. The year 1999 is highlighted since it was in January and late May/early June of 1999 that the thermohaline observations took place.
The high resolution grid Results River Discharge The salinity autumn/winter case validation (wet season) shows that even with climatological river discharges, the model is capable of reproducing the main aspects of the stratification observations model
Summary and Future plans Summary A first realistic modeling configuration was created and validated for the Baía de Todos os Santos, Brazil and adjacent coastal/shelf region The configuration is robust, showing skill for reproducing free surface, currents and thermohaline fields of the shelf-estuary configuration, in time scales from tidal to seasonal A complete and detailed manuscript was submitted for Ocean Modelling (SI on Coastal Ocean Modelling) Future Plans Inclusion of daily riverine discharge and variable bottom drag Use of higher resolution atmospheric forcing The implementation of intertidal capabilities, inclusion of estuarine regions and small embayments inside the bay
References Amorim FN, Cirano M, Soares ID, Lentini CAD. Coastal and shelf circulation in the vicinity of Camamu Bay (14 S), Eastern Brazilian Shelf. Continental Shelf Research, 2011, 31, 108-119. Amorim FN, Cirano M, Soares ID, Campos EJD, Middleton JF. The influence of large-scale circulation, transient and local processes on the seasonal circulation of the Eastern Brazilian Shelf, 13 S. Continental Shelf Research, 2012, 32, 47-61. Amorim FN, Cirano M, Marta-Almeida M, Campos EJD. The Seasonal Circulation of the Eastern Brazilian Shelf between 10 S and 16 S: a modeling approach. Continental Shelf Research, 2013, 65, 121-140.
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