On the Rapid Intensification of Hurricane Wilma (2005)

1. On the Rapid Intensification of Hurricane Wilma (2005) Hua Chen Committee members: Dr. Da-Lin Zhang (Advisor) Dr. James Carton Dr. Chuan Liu (Dean’s Representative) Dr. Xin-Zhong Liang Dr. Kayo Ide Dr. Takemasa Miyoshi

3. Overview of Hurricane Wilma (2005) • Record intensity in the Atlantic basin – 882 hPa • Record intensification rate: 54 hPa/6 h, 83 hPa/12h, • and 97 hPa/24 h (RIDef: > 1.5 hPa/hr) • Record small eye size: 5 kilometer in diameter • Huge storm surge: 12 - 14 feet surge • Torrential rainfall: 1600 mm rainfall/24h at Yucatan peninsula • Above the mean fcst errors: track - 160 km/48 h, 250 km/72 h, and • large intensity underforecast (GFDL: 924 hPa and 50 m s-1).

4. Outline • Numerical prediciton • Model description • Model Verification • Diagnostic analysis • The upper level warm core • Small symmetric eyewall

5. Model Description (WRF-ARW) • Two-way, movable, quadruply nested (27/9/3/1 km),55 levels in the vertical; • Thompson et al. (2004) 3-ice cloud microphysics scheme; • The Betts-Miller-Janjic cumulus scheme for 27 and 9 km; • The YSU PBL scheme; • NOAH surface-layer physics; • Cloud-radiation interaction scheme; • Initial and boundary conditions: The GFDL’s then operational data, except for the specified daily SST; • Integration period: 0000 UTC 18 ~ 0000 UTC 21 October 2005 (72 h) for all the four meshes.

7. The best track (dashed) vs the 72-h predicted track (solid),SST (shaded), SST (00 Z 19 – 00 Z 18; contoured) Predicted Observed NASA/GSFC, 26 March 2012

9. Predicted reflectivity at 1-km altitude Visible Satellite picture A B C D 1900 UTC 18 OCT 1800 UTC 18 OCT

11. Verification against the flight-level observations RMW = 15 km RMW = 7 km Observed Predicted

12. Hypothesis – upper level warm core • An upper level warm core is important for RI; • The upper level warm core results from the descending air in the lower stratosphere due to convective bursts • This upper level warm core is protected by the symmetric divergent outflow at upper level from ventilation; • Convective bursts, driven by high SSTs, play an important role in generating the upper-level warm core.

13. Hypothesis – upper level warm core • An upper level warm core is important for RI; • The upper level warm core results from the descending air in the lower stratosphere due to convective bursts • This upper level warm core is protected by the symmetric divergent outflow at upper level from ventilation; • Convective bursts, driven by high SSTs, play an important role in generating the upper-level warm core.

14. a) Shadings: Temperature perturbation with respect to t = 0; Contours: Potentialtemperature Wind barbs all taken at the eye center. b) Total warming Warming above 380 K Warming below 380 K

15. t = 36 h 380 K 340 K

16. Efficiency of upper level warming Pt T1+∆T T1 T2 T2+∆T Pb Pa

17. Hypothesis – upper level warm core • An upper level warm core is important for RI; • The upper level warm core results from the descending air in the lower stratosphere due to convective bursts • This upper level warm core is protected by the symmetric divergent outflow at upper level from ventilation; • Convective bursts, driven by high SSTs, play an important role in generating the upper-level warm core.

18. RI Post-RI Pre-RI

19. t = 30 h, t = 30.08h The cloud field at z = 17.5 km and CBs. The red circle is the RMW at z = 1 km

20. Vertical cross section of cloud hydrometeors (shaded,g kg-1), storm-relative flow vectors, and vertical motion (downward/dashed every 1 m s-1 and upward/solid every 3 m s-1). NASA/GSFC, 26 March 2012

21. Hypothesis – upper level warm core • An upper level warm core is important for RI; • The upper level warm core results from the descending air in the lower stratosphere due to convective bursts • This upper level warm core is protected by the symmetric divergent outflow at upper level from being ventilated; • Convective bursts, driven by high SSTs, play an important role in generating the upper-level warm core.

22. b a Differences: t = 30 h • Higher altitude of warm core • at t =30 h; • Higher outflow layer at t=30 h; • Higher inflow layer at t=30 h; Common feature: • Warm core is located at the • same altitude as the outflow • layer t = 54 h

23. RI onset Z = 14 km Shading: θ Red contour: Upward motion Blue contour: Downward motion Black circle: RMW at Z = 1 km “W”: warm anomaly

24. Pre-RI Z = 14 km Shading: θ Red contour: Upward motion Blue contour: Downward motion Black circle: RMW at Z = 1 km “W”: warm anomaly

25. Internal gravity wave movie

26. Hypothesis – upper level warm core • An upper level warm core is important for RI; • The upper level warm core results from the descending air in the lower stratosphere due to convective bursts • This upper level warm core is protected by the symmetric divergent outflow at upper level from ventilation; • Convective bursts, driven by high SSTs, play an important role in generating the upper-level warm core.

27. The 18/6/2 km control simulation The SST-1 sensitivity simulation CTL: 3.5 hPh/hr SST-1: 1.9 hPa/hr NASA/GSFC, 26 March 2012

28. Time Series of the number of Intense updrafts 2-km control 2-km SST-1

29. Hypothesis – small symmetric eyewall • The small eye is important; • The symmetric patter is important

30. Hypothesis – small symmetric eyewall • The small eye is important; • The symmetric patter is important

31. Onset of RI Adapted from Schubert and Hack (1982)

32. AAM conservation • Gradient wind balance • solid body rotation

33. Hypothesis – small symmetric eyewall • The small eye is important; • The symmetric patter is important

34. Why does the eyewall becomes from asymmetric to symmetric?

35. Why symmetric pattern is important for RI?

36. How does the eye size contract fast in pre-RI stage? Shading: radar reflectivity contour: Vorticity “A”, “B” denote the rainbands.

37. Small symmetric eyewall forms!

38. Conclusion • WRF model reproduces reasonable well the track, intensity and storm structure given the reasonable configuration; • An upper level warm core is important for the storm to undergo RI because of its efficiency; • The upper level warm core results from the descending air in the lower stratosphere due to convective bursts • This upper level warm core is protected by the symmetric divergent outflow at upper level from ventilation; • Convective bursts, driven by high SSTs, play an important role in generating the upper-level warm core.

39. Conclusion -continued • The small eye size is important in determining RI; • The asymmetric pattern is hostile to RI because it induces tilting and the asymmetric divergent outflow advects warming away from the center; • The change of vertical wind shear with time is a key factor for the trigger of RI since it prevents the formation of a large symmetric eyewall at early stage.

40. Future work • Perform more clear SST sensitivity tests to identify its impact on convective bursts and associated warm core; • Microphysics sensitivity test.

41. Any questions?