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Modelling the Ocean Response to a Tropical Cyclone on Australia's Northwest Shelf

Modelling the Ocean Response to a Tropical Cyclone on Australia's Northwest Shelf. Madeleine Cahill, CMAR Peter Craig, CMAR Mike Herzfeld - CMAR Lou Mason - UTas. Can we model the ocean response to tropical cyclones ?. Tropical cyclones: infrequent, small, energetic

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Modelling the Ocean Response to a Tropical Cyclone on Australia's Northwest Shelf

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  1. Modelling the Ocean Response to a Tropical Cyclone on Australia's Northwest Shelf Madeleine Cahill, CMAR Peter Craig, CMAR Mike Herzfeld - CMAR Lou Mason - UTas

  2. Can we model the ocean response to tropical cyclones ? • Tropical cyclones: infrequent, small, energetic • Dynamic atmospheric models have little skill in generating TCs • Observations of cyclones in Australia are generally land based • In situ observations of ocean response are rare. • Effects are devastating (oil rigs, coastal regions…)

  3. Ocean observations NWS – 1995 current meter deployment xcurrent meter mooring ADCP

  4. Path of TC Bobby

  5. SHOC - CSIRO’s Coastal Ocean Model • 3-D primitive equation hydrodynamic model • Arakawa C-grid • free surface • vertical z coordinates • a choice of turbulence closure schemes Our application • 4km & 20km horizontal grid resolution • 46 z-levels • k-e turbulence closure scheme • Horizontally uniform vertical temperature profile with a 20m mixed layer

  6. Tropical Cyclone Model Double vortex Holland model - track prescribed - radius to maximum winds determined by fitting to available wind and pressure observations

  7. Available marine wind observing sites

  8. Cyclone model fit to wind observations: Site 1

  9. Model fit to wind observations: site 2

  10. Tropical Cyclone Model ParametersRadius to maximum winds Central pressure deficit Two Holland wind fields:Bobby1 (blue),Bobby2 (pink)

  11. Holland wind fields - wind stressmagnitude ocean current vectors (pink)Bobby1 Bobby2

  12. Filtered current vector timeseriesADCP mooring in 125m (central site)

  13. Modelled ocean response at ADCP mooring Wind forcing: Bobby1 Bobby2

  14. Comparing response to two wind fields: Bobby1 (m) and Bobby2 (black) at the ADCP (125m) Alongshore component Cross-Shelf component

  15. Comparing response to Bobby1(m) and Bobby2(black) at offshore mooring (M2 in 300m) Alongshore component Cross-shelf component

  16. Filtered current vector timeseries Offshore mooring in 300m

  17. Modeled response at offshore mooring: windfield1 windfield2

  18. Velocities at ADCP location Observations (blue) v SHOC (mag)

  19. Conclusions • Model-data fit is starting to look pretty good • Model response is very sensitive to TC extent and location Further work • compare SHOC results with ROMS • explore the effect of different vertical mixing schemes (using temperature as well velocity for verification) • There are a further 11 TCs for which we have some current and temperature observations from the NWS.

  20. Thank you Email:madeleine.cahill@csiro.au Web:www.cmar.csiro.au

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