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A model study of the seasonal circulation in the Gulf of Maine

A model study of the seasonal circulation in the Gulf of Maine. Author: Huijie Xue, Fei Chai, and Neal.R.Pettigrew. 1.Introduction. Topography Basins(200m isobath separated). 1.Introduction. Circulation Seasonal variation  Georges eddy, late April summer gulfwide Winter

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A model study of the seasonal circulation in the Gulf of Maine

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  1. A model study of the seasonal circulation in the Gulf of Maine Author: Huijie Xue, Fei Chai, and Neal.R.Pettigrew

  2. 1.Introduction • Topography • Basins(200m isobath separated)

  3. 1.Introduction • Circulation • Seasonal variation Georges eddy, late April summer gulfwide • Winter • Jordan Basin in 1987 • Dynamical factors=> winds winter cooling river discharge Inflow from Scotian shelf Deep inflow of the slope Water (NEC) Tidal mixing Upstream over Scotian shelf(0.35sv for Halifax) • Aim of the paper

  4. 2.Ocean Model • Princeton Ocean Model (POM) • Domain 550km*800km Resolution open boundary 3*4~6*7km • rivers • Time steps 9sec& 414sec topography: Bedford Institute of oceanography (1200m isobar) deep water(ETOPO5)

  5. 2.Ocean Model • Monthly Climatology: July East Coast Forecast System (ECFS) resolution 20km cyclonic over Georges Bank Salinity 33.5&35 (reason) (why no matter)?

  6. 2.Ocean Model • Climatology (Surface forcing): • COADS wind (strength, direction) net inward heat flux net freshwater flux

  7. 3.Model Spinup • With only atmosphere forcing (position of sites) • 3 year kenetic energy variation(20% 1st,2% 2nd) • annual cycle established • Elevation (trend, reason), SST (faster in summer, NEC), Salinity (adjustment time scale)

  8. 4. Seasonal Circulation of the Gulf of Maine • open boundary influence little to interior circulation • atmospheric forcing induced seasonal circulation (spin up, form, maximum, shrink, offshore) • 100m follows the general pattern, topography(200m isobath, basins), cyclonic gyres( stratification explanation: penetration)

  9. 4. Seasonal Circulation in the Gulf of Maine • Two experiments (last 6mon)  • with heat flux, but changing wind direction; • with wind, but with no heat flux) • result: wind: little influence heat flux plays an important role (what’s the role)

  10. 5. Effects of river discharge on the seasonal circulation • combined discharge (single-cell-width channel ) • flows in Mouth of Saint John River, seasonality of the salinity

  11. 5. Effects of river discharge on the seasonal circulation 1st experiment annual cycle enhanced（summer higher, WMC, winter cooler-reason） salinity cycle becomes clear (WMC lowest-reason) ,Seasonality at the four points(seasonality)

  12. 5. Effects of river discharge on the seasonal circulation • generally unaffected • April (offshore), June (near shore, offshore) stronger, other periods weaker, December alike，shrink • 100 meter: weaker (reason)

  13. 6. Effect of the M2 tide on the Seasonal Circulation Mount Desert Land trend of coamplitude 0 phase line(100m isobath), 90 phase line agree well with observation

  14. 6. Effect of the M2 tide on the Seasonal Circulation • strong effect on water-properties • Water level higher nearshore • EMC (temperature decreases, minimum salinity increases) • WMC (minimum salinity change little, period shorter-reason) • GSC (shorter, increases in salinity) Generally the result of mixing increases the salinity 2nd Experiment

  15. February, October-December (reason), Georges Bank 6. Effect of the M2 tide on the Seasonal Circulation

  16. 7. Discussions and Summary--Discussions • description • Problems Strength Direction • Reasons (ECFS) ECFS interfere • Dilution/set-down of sea-surface elevation, causing a southwestward • flows from SJ River (next page)

  17. 7. Discussions and Summary--Discussions Without tides Tidal mixing Low salinity missing With tides Seasonality cyclonic Too high salinity SJ river partially responsible

  18. 7. Discussions and Summary--Summary • Conclusions: • surface heat flux plays an important role in regulating the annual cycle of GOM circulation • river discharge helps to establish a clear annual cycle in surface salinity • M2 tides contributes to the seasonal circulation in several ways as generating the Georges Bank gyre and Browns Bank gyre, and enhancing the coastal current through tidal rectification and tidal mixing. Moreover, the tidal mixing results in the spindown of the circulation and tend to increase the salinity along the coast.

  19. Thanks !

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