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Dynamics of Spencer Gulf: Effects of Evaporation, Heating and Tides Carlos Teixeira & John Middleton 2012 ROMS/ TOMS Workshop – 22/10/2012.

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Presentation on theme: "Dynamics of Spencer Gulf: Effects of Evaporation, Heating and Tides Carlos Teixeira & John Middleton 2012 ROMS/ TOMS Workshop – 22/10/2012."— Presentation transcript:

1 Dynamics of Spencer Gulf: Effects of Evaporation, Heating and Tides Carlos Teixeira & John Middleton 2012 ROMS/ TOMS Workshop – 22/10/2012

2 During summer, gulf and shelf waters have similar density and there is no exchange. Contours of near-bottom salinity (16-23 June Lennon et al. 1987) During winter, the gulf waters are cooled and become denser than the shelf waters. This dense water flows out to the adjacent shelf. The exchange occurs as pulses with ~14 days period due to the spring-neap tide modulation. Background Spencer Gulf is a large inverse estuary.

3 Sea Surface Temperature from satellite measurements Summertime Scenario Previous works suggested that the upwelled waters in the shelf block the gulf outflow during summer.

4 Objective: Explain the exchange between the Spencer Gulf and the shelf.Explain the exchange between the Spencer Gulf and the shelf. The importance of the fresh water flux, heat flux and tides to the circulation within the gulf and to the water exchange;The importance of the fresh water flux, heat flux and tides to the circulation within the gulf and to the water exchange;

5 Fresh Water Flux (E-P),Fresh Water Flux (E-P), FWF + Net Heat FluxFWF + Net Heat Flux FWF + NHF + TidesFWF + NHF + Tides Numerical experiments: Methodology: Simulations of increasing complexity, where only one parameter is changed at a time and the results compared and contrasted.Simulations of increasing complexity, where only one parameter is changed at a time and the results compared and contrasted.

6 ROMS model ROMS model 5 x 5 Km horizontal resolution, 30 sigma levels 5 x 5 Km horizontal resolution, 30 sigma levels Started from rest, temperature and salinity from CSIRO CARS2006 dataset; Started from rest, temperature and salinity from CSIRO CARS2006 dataset; Chapman and Flather Radiation BC’s; Chapman and Flather Radiation BC’s; Salinity and temperature clamped to CARS data and total volume conservation; Salinity and temperature clamped to CARS data and total volume conservation;

7 FWF (E – P) Model forced only with climatologically monthly averages of evaporation – precipitation from OAFLUX + MetStationsModel forced only with climatologically monthly averages of evaporation – precipitation from OAFLUX + MetStations Temperature kept constant;Temperature kept constant; Model ran for 10 years;Model ran for 10 years;

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9 Fresh Water Flux

10 Eddies due to baroclinic instability The slope in the density field produce an excess of potential energy.The slope in the density field produce an excess of potential energy. Diameter ~ 20 Km and propagate at a rate of 4 km/ dayDiameter ~ 20 Km and propagate at a rate of 4 km/ day

11 Up-gulf velocities from year 2 to 10. Eddies related to 14 to 32 days periods;Eddies related to 14 to 32 days periods; Occurring throughout the year;Occurring throughout the year; More energy during summer time;More energy during summer time;

12 FWF + NHF Model forced with climatologically monthly averages of FWF plus NHF from OAFLUX + MetStationsModel forced with climatologically monthly averages of FWF plus NHF from OAFLUX + MetStations

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14 Fresh Water + Net Heat Flux Fresh Water Flux

15 Up-gulf velocities from year 2 to 10. Eddies again related to 14 to 32 days periods;Eddies again related to 14 to 32 days periods; Now, concentrated during wintertime;Now, concentrated during wintertime;

16 FWF + NHF + Tides Model forced with climatologically monthly averages of FWF plus NHF plus tides from TPX07.2Model forced with climatologically monthly averages of FWF plus NHF plus tides from TPX07.2 Four most important tidal constituents (M2, S2, O1, K1) used to force the model.Four most important tidal constituents (M2, S2, O1, K1) used to force the model. **The region present a “dodge” tide with no tidal currents for 2-3 days during neaps (~ every 14 days).

17 M2 Tidal Amplitudes Spencer Gulf M2 Tidal Phases Spencer Gulf

18 Evaporation + heat flux Evaporation + heat flux + tides

19 Modeled Density summertime Modeled Density wintertime

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22 Up-gulf velocities from year 2 to 10. Eddies now related to 14 days periods;Eddies now related to 14 days periods; Again concentrated during wintertime;Again concentrated during wintertime;

23 Tidal turbulence break down the stratification during spring tides. Tidal turbulence break down the stratification during spring tides. During neap (dodge) tides stratification is build and baroclinic instability is created leading to eddies. During neap (dodge) tides stratification is build and baroclinic instability is created leading to eddies.

24 1 = 5 cm s -1 Spring-Neap tidal cycle modulate the circulation;Spring-Neap tidal cycle modulate the circulation; Highest speeds during neaps when density gradients are larger;Highest speeds during neaps when density gradients are larger;

25 Summary Evaporation is able to keep the salinity in the gulf constant;Evaporation is able to keep the salinity in the gulf constant; Production of eddies throughout the year due baroclinic instabilities;Production of eddies throughout the year due baroclinic instabilities; Highest densities and velocities during summertimeHighest densities and velocities during summertime Heat flux force a time modulation of the density and the circulation;Heat flux force a time modulation of the density and the circulation; No exchange with the shelf during summer;No exchange with the shelf during summer; Eddies only during wintertime;Eddies only during wintertime; Highest densities and velocities during wintertime;Highest densities and velocities during wintertime; Spring-neap tidal cycle modulates the intensity of the stratification and the circulation;Spring-neap tidal cycle modulates the intensity of the stratification and the circulation; Density (and salinity) has a large increase;Density (and salinity) has a large increase; Eddies only during wintertime now with 14 days period;Eddies only during wintertime now with 14 days period; Highest velocities during neap tides;Highest velocities during neap tides;

26 Observational Side: 6 months of ADCP and near bottom CTD data (SAIMOS)6 months of ADCP and near bottom CTD data (SAIMOS)

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29 Summary The results support the existence of eddies; Summer blockage of the gulf-shelf exchange; Spring-neap modulation of the circulation and exchange with the shelf. The presence of eddies in Spencer Gulf is new and in line with their Mediterranean cousins, we suggest the eddies here be named Speddies.

30 Thanks!!


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