1. Hurricane structure and intensity change : Effects of wind shear and Air-Sea Interaction M é licie Desflots Rosenstiel School of Marine & Atmospheric Science 4600 Rickenbacker Causeway, Miami, FL, 33149-1098

2. What controls Hurricane Intensity ? Inner core (eye and eyewall) dynamics and rainbands (Theoretical and modeling work, e.g., Montgomery& Kallenbach 1997, Schubert et al. 1999, and recent field program – RAINEX, Houze et al. 2006, Chen 2006) Environmental conditions -vertical wind shear (e.g., Frank&Ritchie 1999, Black et al. 2002, Rogers et al. 2003, Chen et al. 2006, Desflots and Chen 2006) -moisture distribution -sea surface temperature (upper ocean heat content), surface properties, etc. (Theoretical, observational, and modeling work, e.g., Emanuel 1995, Bao et al. 2000, and recent results from CBLAST, Black et al. 2006, Chen et al. 2006)

3. Outline  Model and data  Effect of vertical wind shear on hurricane intensity  Importance of air-sea interaction for hurricane intensity (sensitivity to sea-spray parameterization)  Conclusions

4. Model ATMOS. MODEL (MM5) OCEAN MODEL (3DPWP) WAVE MODEL (WAVEWATCH III) Wave-induced stress Surface wind Heat & Moisture fluxes SST Current velocity Wave-Induced stress

5. Data Storm Name Storm Year Number of match Erika199710/17 Bonnie199823/25 Floyd19996/6 Fabian20034/4 Frances20042/2 Jeanne20043/3 Dennis20055/5 Rita200515/17 79 co-located dropsondes +AXBT Data  68

6. Effect of vertical wind shear on hurricane intensity

7. Effect of Vertical Wind Shear on TCs’ intensity e.g. Simpson and Riehl 1958; Gray 1968; Willoughby 1984; Marks et al 1992; Franklin et al. 1993; Jones 1995,2000a, 2000b; DeMaria 1996; Gamache et al. 1997; Frank and Ritchie 2001; Black et al. 2002; Corbosiero and Molinary 2002; Rogers et al 2003; Wong and Chan 2004 ; Lonfat 2004; Chen et al. 2006 Mechanisms: 1) vortex tilt and 2) shear-induced secondary circulation Low shear High shear Shear-Induced Rainfall Asymmetry (Chen et al. 2006) (Global composite from TRMM and SHIPS data)

8.  MM5: the 5 th generation high resolution, non- hydrostatic PSU/NCAR mesoscale model  Multi-nested, vortex- following domains with grid resolution of 15,5,1.67, 0.55 km, respectively  28 vertical sigma-levels Model description

9. Model initialization  Initialized at 0000 UTC, 10/01/02, integrated for 72 hrs.  NCEP global 1°x1° analysis is used as initial and lateral boundary conditions  Time varying SST from SSMI/satellite (1/4°)  A vortex relocation procedure, similar to Liu et al. (1997), is used at the initial time.

10. Track

11. Intensity landfall Best Track 5 km 1.67 km 0.55 km

13. Evolution of the Intensity of Hurricane Lili (2002) Time landfall Sea Level Pressure Radius Tangential Velocity in m/s Rain Rate in mm/h

14. Shear Analysis from MM5 (1) (2) (1) (2) Vertical wind shear vector Storm motion

15. Vortex Tilt/ Temperature perturbations T/W at 550 hPa Rain rate 10/02 21Z 10/03 03Z 10/02 13Z

16.  Combine effect of the increasing vertical wind shear and the vertical wind shear direction created a rainfall asymmetry  The vertical wind shear weakened the storm’s intensity Effect of Vertical Wind Shear on Hurricane Lili

17. Importance of the of air-sea interactions for hurricane intensity

18. Hurricanes intensity and Air-Sea Interaction Ocean coupling by reducing the amount of available heat fluxes reduces the storm intensity (e.g., Chen et al. 2006) Sensitivity to sea spray parameterization in a coupled model (e.g., Bao et al. 2000, Kepert, 2001)

19. Importance of Air-Sea Fluxes in Hurricane Intensity Energy source (enthalpy) and sink momentum/dissipation) for hurricanes The balance between the two can potentially affect hurricane intensity They are a good constraint to develop and evaluate coupled air-sea models for hurricane intensity forecasting

20. Air-Sea Fluxes formulation Momentum flux Sensible Heat flux Latent Heat flux In a turbulent boundary layer the turbulent fluxes can be approximated to bulk fluxes :

21. Behavior of the exchange coefficients at high wind speed The drag coefficient levels off at high wind speed (Powell et al. 2003; Donelan et al. 2004) 10 3 C E CBLAST Observations: Black et al. (2006), Drennan et al. (2006), French et al. (2006) C D

22. Total Surface Heat Fluxes Uncoupled model Coupled model Bulk fluxes estimates from GPS dropsondes and AXBTs

23. Air-Sea temperatures Coupled ModelObservations SST Sea-air temperature difference

24. Are the total heat fluxes correlated to hurricane intensity or local wind speed ? Wind speed in m/s Erika 970908 Bonnie 980821 Bonnie 980824 Bonnie 980825 Bonnie 980826 Floyd 990913 Floyd 990914 Fabian 030902 Fabian 030903 Fabian 030904 Frances 040901 Jeanne 040925 Dennis 050709 Dennis 050710 Rita 050922 Rita 050923 ****** XxXx Tropical Storm Cat. 1-2 Major hurricanes FR FL RL RR

25. Air-sea Fluxes in the eyewall Floyd (1999) Frances (2004) Bonnie (1998) Lili (2002) Heat fluxes SLP

26. Air-sea Fluxes coupled eyewall Floyd Bonnie FrancesLili

27. Air-sea Fluxes within 200km radius Lili (2002) Floyd (1999) Frances (2004) Bonnie (1998) Heat fluxes SLP

28. Effect of Sea Spray on surface heat fluxes Fairall et al. 1994 : The effect of sea spray on the surface energy transports over the ocean. Global Atmos. Ocean Syst., 2, 121-142 Bao et al. 2000 : Numerical Simulations of Air-Sea Interaction under High Wind Conditions Using a Coupled Model : A study of Hurricane Development, Mon. Wea. Rev.,128, 2190-2210 On the sensible heat flux : -The sea spray droplet cools from the sea temperature to the air temperature (or to Tw’) and gives up sensible heat TO the atmosphere - to evaporate the sea spray some sensible heat flux FROM the atmosphere is required - frictional terms due to waves On the latent heat flux : - when the sea spray evaporates it gives up some latent heat flux TO the atmosphere

29. Sensitivity to sea spray Frances without Sea SprayFrances with Sea Spray Air-sea Fluxes in the eyewall Air-sea Fluxes within 200km radius SLP Heat fluxes

30. Conclusions Strong wind shear-induced asymmetry in rainfall (convective heating) and vortex circulation is a major limiting factor on hurricane intensity Observed surface enthalpy flux has a large storm-to-storm variability as well as spatial variability within each storms Storm-averaged total surface enthalpy flux is not a good predictor of hurricane intensity or intensity change Inner-core (eye and eyewall) structure and dynamics dominate the rapid intensification process, which is sensitive to the surface enthalpy flux in the eyewall region Coupled atmosphere-wave-ocean model can produce the general characteristics of observed surface fluxes. However, parameterizations of the air-sea fluxes remain to be a challenge, especially sea spray due to the lack of observations in high winds.

31. Part of this work was supported by a research grant from the Office of Naval Research (N00014-01-1-0156) My advisor : Dr. Shuyi Chen My committee members : Drs. David Nolan, Mark Donelan, James Price, Frank Roux and Will Drennan Drs. Wei Zhao, Jian-Wien Bao Mike Black for help to process the dropsondes HRD and CBLAST program for collecting precious data Jun Zhang for helpful discussion Thank to all the people who helped me one way or another Acknowledgements