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The Extratropical Transitions of Danielle and Earl (1998)

The Extratropical Transitions of Danielle and Earl (1998). Ron McTaggart-Cowan J.R. Gyakum, M.K. Yau. The Extratropical Transitions of Danielle and Earl (1998) – sensitivity to remnant vortex modifications. Ron McTaggart-Cowan J.R. Gyakum, M.K. Yau. Outline. Motivation and ET background

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The Extratropical Transitions of Danielle and Earl (1998)

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  1. The Extratropical Transitions of Danielle and Earl (1998) Ron McTaggart-Cowan J.R. Gyakum, M.K. Yau

  2. The Extratropical Transitions of Danielle and Earl (1998) – sensitivity to remnant vortex modifications Ron McTaggart-Cowan J.R. Gyakum, M.K. Yau

  3. Outline • Motivation and ET background • Case description • Important upstream features • Important downstream features • PVmc introduction • Importance of remnant vortex • Discussion

  4. Outline • Case description • Important downstream features • PVmc introduction • Importance of remnant vortex • Discussion

  5. ET Background • 50% of Atlantic hurricanes ET • The resulting storm is often more intense than the hurricane • ETs are very hard to forecast in real time

  6. Case Description • Danielle reaches five intensity maxima – 55 ms-1 • Earl develops in the Gulf of Mexico and only reaches Category 2 before landfall Danielle Earl

  7. Case Description • Both storms transition and reintensify rapidly between 0000 UTC 5 September and 0000 UTC 7 September Earl: water vapour image from 1200 UTC 6 September

  8. Case Description • Both storms transition and reintensify rapidly between 0000 UTC 5 September and 0000 UTC 7 September Danielle: infrared image from 1200 UTC 6 September

  9. Case Description • The MC2 model is used to sim-ulate the ETs of Danielle and Earl • Traditional synoptic diagnostics provide insight into the transition process • 250 hPa winds, 1000-500 hPa thickness, and SLP serve as an introduction to the case

  10. Case Description • The MC2 model is used to sim-ulate the ETs of Danielle and Earl Valid 0000 UTC 5 Sept 00 h

  11. Case Description • The MC2 model is used to sim-ulate the ETs of Danielle and Earl Valid 1200 UTC 5 Sept 12 h

  12. Case Description • The MC2 model is used to sim-ulate the ETs of Danielle and Earl Valid 0000 UTC 6 Sept 24 h

  13. Case Description • The MC2 model is used to sim-ulate the ETs of Danielle and Earl Valid 1200 UTC 6 Sept 36 h

  14. Case Description • The MC2 model is used to sim-ulate the ETs of Danielle and Earl Valid 0000 UTC 7 Sept 48 h

  15. Review of PV • Ertel PV (1954) • Conserved for adiabatic, inviscid flows • Invertible given: • Boundary conditions • Balance equation • Background state 400 hPa PV Valid 0000 UTC 5 Sept

  16. Upstream Features • PV features are identified and removed • Sensitivity of ET to each feature is determined

  17. Upstream Features • The upstream trough is the most important feature • The ex-hurricane plays a secondary role

  18. Downstream Features • Simultaneous ET and intensifica-tion simulated with MC2 model • The dynamic tropopause (DT, 2PVU) potential temperature describes the upper-level dynamics • Near-surface potential (850 hPa) temperatures act as surrogate PV at lower levels

  19. Downstream Features • Simultaneous ET and intensifica-tion simulated with MC2 model Valid 0000 UTC 5 Sept 00 h

  20. Downstream Features • Simultaneous ET and intensifica-tion simulated with MC2 model Valid 1200 UTC 5 Sept 12 h

  21. Downstream Features • Simultaneous ET and intensifica-tion simulated with MC2 model Valid 0000 UTC 6 Sept 24 h

  22. Downstream Features • Simultaneous ET and intensifica-tion simulated with MC2 model Valid 1200 UTC 6 Sept 36 h

  23. Downstream Features • Simultaneous ET and intensifica-tion simulated with MC2 model Valid 0000 UTC 7 Sept 48 h

  24. Downstream Features • With a benign downstream state, the transition is tropical mode Valid 0000 UTC 7 Sept 48 h

  25. Downstream Features • With only a simplified NA jet/front, the transition is baroclinic mode Valid 0000 UTC 7 Sept 48 h

  26. PVmc Introduction • Our upstream study found small sensitivity to the remnant TC • Removal of both dry dynamics and moisture is required • Moist Component PV links dynamics and moisture in a balanced way

  27. PVmc Introduction 850 hPa PVmc and winds (kts) for control initial conditions • PVmc highlights regions of dynamic and thermodynamic importance 00 h

  28. Remnant Vortex • Combining PV and PVmc modifications allows for the complete removal of the TC remnants • The tropical mode ET (Danielle) should be more sensitive to the moisture modifications

  29. Remnant Vortex Control Danielle Removed 850 hPa geopotential heights (3 dam) and specific humidity (g/kg) in the initial conditions before (left) and after (right) the complete removal of ex-hurricane Danielle. 00h

  30. Remnant Vortex Control Danielle Removed 850 hPa geopotential heights (3 dam) and specific humidity (g/kg) valid 1200 UTC 5 September before (left) and after (right) the complete removal of Danielle. 12h

  31. Remnant Vortex Control Danielle Removed 850 hPa geopotential heights (3 dam) and specific humidity (g/kg) valid 0000 UTC 6 September before (left) and after (right) the complete removal of Danielle. 24h

  32. Remnant Vortex Control Danielle Removed 850 hPa geopotential heights (3 dam) and specific humidity (g/kg) valid 1200 UTC 6 September before (left) and after (right) the complete removal of Danielle. 36h

  33. Remnant Vortex Control Danielle Removed 850 hPa geopotential heights (3 dam) and specific humidity (g/kg) valid 0000 UTC 7 September before (left) and after (right) the complete removal of Danielle. 48h

  34. Remnant Vortex • Removal of Danielle results in much weaker in-situ development Control Danielle Removed Sea level pressure and sensible heat flux (Wm-2) valid 0000 UTC 6 September 24h

  35. Remnant Vortex • Small positive heat fluxes ahead of Danielle may lead to some deepening Control Danielle Removed Sea level pressure and latent heat flux (Wm-2) valid 0000 UTC 6 September 24h

  36. Remnant Vortex Control Earl Removed 850 hPa geopotential heights (3 dam) and specific humidity (g/kg) in the initial conditions before (left) and after (right) the complete removal of ex-hurricane Earl. 00h

  37. Remnant Vortex Control Earl Removed 850 hPa geopotential heights (3 dam) and specific humidity (g/kg) valid 1200 UTC 5 September before (left) and after (right) the complete removal of ex-hurricane Earl. 12h

  38. Remnant Vortex Control Earl Removed 850 hPa geopotential heights (3 dam) and specific humidity (g/kg) valid 0000 UTC 6 September before (left) and after (right) the complete removal of ex-hurricane Earl. 24h

  39. Remnant Vortex Control Earl Removed 850 hPa geopotential heights (3 dam) and specific humidity (g/kg) valid 1200 UTC 6 September before (left) and after (right) the complete removal of ex-hurricane Earl. 36h

  40. Remnant Vortex Control Earl Removed 850 hPa geopotential heights (3 dam) and specific humidity (g/kg) valid 0000 UTC 7 September before (left) and after (right) the complete removal of ex-hurricane Earl. 48h

  41. Remnant Vortex • Removal of Earl results in a strong development, but with weakened frontal structures Control Earl Removed 850 hPa potential temperature and 300 hPa PV valid 1200 UTC 6 September 36h

  42. Remnant Vortex • Removal of Earl results in a strong development, but with weakened frontal structures Control Earl Removed 850 hPa potential temperature and 300 hPa PV valid 0000 UTC 7 September 48h

  43. Remnant Vortex • Baroclinic mode (Earl) is insensitive to vortex removal • Tropical mode (Danielle) is influenced by the structure of the remnant TC

  44. Discussion • Two transition modes identified: tropical and baroclinic • Upstream trough is necessary and sufficent for baroclinic mode ET • Tropical mode ET also requires remnant TC vortex • Downstream jet modulates the transition mode

  45. Discussion • Advanced diagnostic tools are required for the investigation of ET dynamics and thermo-dynamics …

  46. Summary • The simultaneous transition and reintensification of Danielle and Earl is simulated • Two distinct modes of transition are found: baroclinic and tropical • Baroclinic mode transitions are found to be less sensitive to remnant vortex removal

  47. Discussion The sensitivity of extratropical transition events to the removal of the remnant TC feature depends strongly on the mode of transition

  48. Dynamic tropopause (2 PVU) and 850 hPa equivalent potential temperature

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