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

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Presentation on theme: "The Extratropical Transitions of Danielle and Earl (1998) Ron McTaggart-Cowan J.R. Gyakum, M.K. Yau."— Presentation transcript:

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

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

3 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

4 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

5 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

6 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

7 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

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

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

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

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

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

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

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

15 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 Downstream Features

16 Simultaneous ET and intensifica- tion simulated with MC2 model 00 h Valid 0000 UTC 5 Sept

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

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

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

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

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

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

23 PV mc 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

24 PVmc Introduction PV mc highlights regions of dynamic and thermodynamic importance 850 hPa PV mc and winds (kts) for control initial conditions 00 h

25 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

26 Remnant Vortex ControlDanielle 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.

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

28 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

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

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

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