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Modeling the Generation of Haida Eddies

Modeling the Generation of Haida Eddies. Emanuele Di Lorenzo 1 , Mike Foreman 2 , Bill Crawford 2 1 Scripps Institution of Oceanography, UCSD, San Diego 2 Institute of Ocean Sciences, Sidney BC. What are Haida Eddies?. Formed off Queen Charlotte Islands clockwise rotation

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Modeling the Generation of Haida Eddies

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  1. Modeling the Generation of Haida Eddies Emanuele Di Lorenzo1, Mike Foreman2, Bill Crawford2 1 Scripps Institution of Oceanography, UCSD, San Diego 2Institute of Ocean Sciences, Sidney BC

  2. What are Haida Eddies? • Formed off Queen Charlotte Islands • clockwise rotation • heights up to 40cm above background ocean • diameters up to 200km • depth to at least 1000m • warmer & fresher • can last more than two years

  3. Importance • carry plankton, larvae, & nutrients offshore • reduce productivity on shelf but increase productivity offshore • Pacific cod recruitment in Hecate Strait shows strong negative correlation with mean sea level previous winter • re-stock fish populations around seamounts • fishery managers would like predictive capability

  4. Overview • Background &importance • Previous studies • Model details • Simulations: • annual cycle • generation mechanism • sensitivity studies • Future work • Summary

  5. Previous Generation Studies • Thomson & Wilson (1987) • tidal residual eddy west of CSJ • Thomson & Gower (1998) satellite observations • baroclinic instability from reversal in poleward winds • Melson et al (1999) & Murray et al (2001) models (NRL) • baroclinic instability: • relaxation of poleward wind or Kelvin waves • BUT coastline omitted inland seas • Crawford et al. (2001) analysis • outflows past Cape St James • lab experiments of Cenedese & Whitehead (2000)

  6. Region of Interest & Data Locations

  7. Model Details • ROMS: • 8 km horizontal resolution • 20 vertical levels • no tides • NCEP or Faucher et al (1999) monthly average winds • radiation/relaxation to TS climatology on boundaries (Marchesiello et al, 2001) • initial & open boundary conditions from Levitus et al (1994) monthly climatology

  8. Annual Cycle Simulations • 12 year run with repeat annual cycle forcing of wind, boundary TS, & nudged surface heat flux

  9. Annual Cycle Simulations (cont’d) • Model phase lag comparison vs tide gauges • 0° = Jan 1 • max difference  1 month (30°) • model amps (cm) too small • coarse resolution, underestimated forcing (NCEP winds nearshore ?)

  10. 200 201 202 203 204 205 206 207 8.5 6.5 208 209 210 211 212 213 214 215 8.5 6.5 216 217 218 219 220 221 222 223 8.5 6.5 224 225 226 227 228 229 230 231 8.5 6.5 Eddy Generation Mechanism • Constant Jan forcing • 5-day time sequences of SSH & SST • distinct small eddies formed at 200, 205, 211, 216, 222 • all except 222 merge • strong eddies form during times of stronger southward flows east of CSJ

  11. Sensitivity Tests • All performed with constant Jan forcing: • average SSH from previous run • constant f: eddies formed but drift northward along topography • barotropic: no eddies formed, flow follows depth contours

  12. Sensitivity Tests (cont’d) • constant depth: no eddy • constant depth & artificial coast in Hecate: standing eddy - no detachment/drift westward • but meanders in northward flow do produce eddies that drift westward • 2nd order advection instead of 3rd: strong eddies not formed - anticyclonic circulation quickly dissipates • lots of animations on http://horizon.ucsd.edu/movies/haida

  13. Future Work • finer resolution • tides & buoy winds • tidal speeds over 1m/s east of CSJ  residual eddies • better nearshore winds • simulation of 1997-98 El Nino

  14. Summary • Haida Eddies generated by advection of buoyant water around Cape St. James • in winter when winds are toward NW • with strong flows, several smaller eddies can merge • important biologically • previous model simulations incomplete BUT “baroclinic instability” from wind relaxation may be generation mechanism elsewhere along shelf • ROMS • reproduced seasonal signal & revealed relevant generation processes • further studies planned with higher resolution, better winds, & tides • more details in Di Lorenzo et al, submitted to DSRII

  15. Acknowledgements • Rick Thomson: current meter & CTD data • Josef Cherniawsky: TP data • Patrick Cummins, John Morrison, Frank Whitney: helpful discussions • Trish Kimber: figures • partial funding from NOAA/NASA (EDL), SSF/DFO (MF & BC)

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