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IMPACTS OF TURBULENCE ON HURRICANES (ONR-BAA-09-012) PI: Yongsheng Chen, York University, Toronto, Ontario, Canada Co-PIs: George H. Bryan and Richard.

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Presentation on theme: "IMPACTS OF TURBULENCE ON HURRICANES (ONR-BAA-09-012) PI: Yongsheng Chen, York University, Toronto, Ontario, Canada Co-PIs: George H. Bryan and Richard."— Presentation transcript:

1 IMPACTS OF TURBULENCE ON HURRICANES (ONR-BAA-09-012) PI: Yongsheng Chen, York University, Toronto, Ontario, Canada Co-PIs: George H. Bryan and Richard Rotunno, National Center for Atmospheric Research, Boulder, Colorado, USA NOPP Progress Report February 25, 2011

2 Agenda 1.Background 1.New work 1.Next steps

3 1. Background

4 Hurricane Simulation Models Fast, simple, but all effects of nonaxisymmetric motions must be somehow represented Axisymmetric Tangential velocity from an axisymmetric numerical model

5 Axisymmetric Model Sensitivity of Wind Speed to Mixing Length l h Bryan and Rotunno (2009 MWR)

6 What is ? There are no observations of radial turbulent fluxes in a hurricane

7 Marks et al. (2008, MWR) Reflectivity (dBZ) at 1726 UTC

8 Marks et al. (2008, MWR)

9 Davis et al. (2008 MWR) Radar Reflectivity at z=3km a)WRF b)WRF c)ELDORA Hurricane Simulation Models Three-Dimensional Mesoscale Forecast Model Vortex asymmetries computed, but effects of small-scale (< 1000m) turbulent motions must be somehow represented

10 y[ km ] WRF Model Idealized TC resolution study, 10-m Wind Speed t=9.75d max=61.5 max=121.7max=86.2 max=86.7 Rotunno et al. (2009 BAMS)

11 Regimes of Numerical Modeling* 1/ Δ meso 1/ Δ LES 1/ l Mesoscale limit LES limit the “terra incognita” k F(k) *Wyngaard (2004 JAS)

12 37km Turbulent fluxes computed, but high resolution (<100m) required Hurricane Simulation Models Large Eddy Simulation

13 Idealized TC: f-plane zero env wind fixed SST Nested Grids WRF Model Physics: WSM3 simple ice No radiation Relax to initial temp. Cd (Donelan) Ce (Carlson-Boland) Ce/Cd ~ 0.65 YSU PBL LES PBL Domain 6075km 1500km 1000km 333km 111km 37km 50 vertical levels  z=60m~1km Ztop=27km Rotunno et al. (2009 BAMS)

14 10-m Wind Speed 37km Max=85.5Max=82.3Max=83.7 instantaneous 1-min average max=121.7max=78.8 Rotunno et al. (2009 BAMS)

15 Vorticity Magnitude

16 10-m Tangentially Averaged Wind Speed vs Grid Interval Rotunno et al. (2009 BAMS)

17 2. New Work

18 Stretched structured grid In center: dx = dy =1.0km (cloud-resolving) 3D version of axisymetric model of Bryan and Rotunno (2009 MWR) 128 km Another approach for high-resolution is grid stretching

19 Reflectivity at surface (shaded) and w at 1 km AGL (contours) Compare axisymmetric results with 3D solutions at similar resolution (dx=dy=1km) on Cartesian grid

20 Axi. vs. 3D Sol’n Sensitivity to l h (using l v = 200 m) NOTE: in ARW: l h = Δx / 4

21 (m/s) at 1 km AGL (at level of maximum )

22 Summary of cloud-scale (dx=dy=1 km) 3D simulations Although 3D V max is systematically lower than that in the axisymmetric model, it is still very sensitive to parameterized horizontal diffusion In terms of typical mesoscale-model (e.g. WRF) parameters, hurricane intensity is sensitive to l h

23 Stretched structured grid In center: dx = dy =0.62km (Large Eddy Simulation) 3D version of axisymetric model of Bryan and Rotunno (2009 MWR) 49 km LES

24 w (m/s) at z = 1 km: dx= 1000m

25 w (m/s) at z = 1 km: dx= 62.5 m

26 Subgrid-scale tke: Resolved-scale tke:

27 with two different resolutions:

28

29 azimuthal averagegrid-scale TC Vortex grid-scale waves & turbulence Estimation of Eddy Viscosity for Mesoscale Models using LES Results

30 turbulence length scale ( l h ): 3D, dx= 62.5 m

31 sensitivity to horizontal turbulence intensity: max observed

32 New Work Summary Parameterized turbulence in the eyewall of hurricanes reduces hurricane intensity even with 3D cloud-resolving (dx=1km) resolution. Large Eddy Simulations using a different model and different resolution-enhancement technique produce results consistent with previous ones indicating that very high resolution (dx< 100 m) in three dimensions is required to simulate turbulent processes Analysis of the new LES indicates l h ~ 1000 m

33 3. Next Steps Higher-res LES, vary SST, moving hurricane…


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