1. Jian-Wen Bao (NOAA/ESRL/PSD) Sara A. Michelson (NOAA/ESRL/PSD) S. G. Gopalakrishnan (NOAA/AOML/HRD) In Collaboration with Frank Marks (NOAA/AOML/HRD) Vijay Tallapragada (NOAA/NCEP/EMC) Controlling Factors of the Radius of Maximum Winds in HWRF Presented at The 65 th Interdepartmental Hurricane Conference Miami, FL, 02 March 2011

2. Outline 1. Motivation and methodology 2. Sensitivity to the size of the initial vortex 3. Sensitivity to vertical and horizontal diffusion 4. Sensitivity to diabatic forcing 5. Summary

3. Courtesy of M. Shapiro Motivation: a holistic understanding of the HWRF model characteristics

4. Courtesy of M. Shapiro Motivation: a holistic understanding of the HWRF model characteristics

5. Methodology: idealized case study f plane located at 12.5ºN A prescribed axisymmetric vortex: — maximum sfc tangential wind: 15 m/s — radius of sfc maximum wind: 90 km Quiescent environment thermally corresponding to the Jordan sounding with a constant sea surface temperature of 29ºC Initial mass and wind fields derived by solving the nonlinear balance equation for the prescribed vortex (Wang 1995, MWR) Model grid spacing: dx = dy = 0.06, 0.02 (~9 km, ~ 3 km) kx = 43 (NMM sigma-p levels) 9 km 3 km 55 o

6. Yellow Squares = Initial vortex:50 km Lime Green Squares = Initial vortex:70 km Magenta Squares = Initial vortex:90 km Light Blue Circles = Initial vortex:110 km Brown Circles = Initial vortex:130 km Purple Squares = Initial vortex:150 km Black Squares = Knaff and Zehr (2007) Sensitivity to the size of the initial vortex Minimum SLPMax. Surface Wind speedPressure-Wind Relationship Radius of Maximum Surface Wind Boundary Layer Scheme Radiation Scheme Convective Parameterization Scheme Microphysics Scheme GFSNCARSASFerrier

7. Initial vortex radius: 90 kmInitial vortex radius: 50 km Initial vortex radius: 150 km Sensitivity to the size of the initial vortex: 60-72 hour Azimuthally Averaged Tangential and Radial Wind Speed and Circulation Vectors Initial vortex radius: 70 km Initial vortex radius: 110 kmInitial vortex radius: 130 km

8. Sensitivity to Horizontal Diffusion Magenta Squares = Default Horizontal Diffusion Blue Squares = 0.5 × Horizontal Diffusion Green Squares = 1.5 × Horizontal Diffusion Gray Squares = 2.0 × Horizontal Diffusion Dark Brown Squares= 4.0 × Horizontal Diffusion Black Squares = Knaff and Zehr (2007) Max. Surface Wind SpeedPressure-Wind Relationship Radius of Maximum Surface Wind Boundary Layer Scheme Radiation Scheme Convective Parameterization Scheme Microphysics Scheme GFSNCARSASFerrier Minimum SLP

9. Sensitivity to Horizontal Diffusion: 60-72 hour Azimuthally Averaged Tangential and Radial Wind Speed and Circulation Vectors 0.5 × Hor. Diffusion1.5 × Hor. DiffusionDefault Hor. Diffusion 4.0 × Hor. Diffusion 2.0 × Hor. Diffusion

10. Sensitivity to Vertical Diffusion Magenta Squares = Default Light Blue Squares= 2 × DKU, 2 × DKT Brown Squares= 0.5 × DKU, 1 × DKT Dark Blue Squares=0.5 × DKU, 0.5 × DKT Black Squares = Knaff and Zehr (2007) Max. Surface Wind speedPressure-Wind Relationship Radius of Maximum Surface Wind Boundary Layer Scheme Radiation Scheme Convective Parameterization Scheme Microphysics Scheme GFSNCARSASFerrier Minimum SLP

11. Default 2 × DKU and 2 × DKT 0.5 × DKU and 0.5 × DKT0.5 × DKU and 1 × DKT Sensitivity to Vertical Diffusion: 60-72 hour Azimuthally Averaged Tangential and Radial Wind Speed and Circulation Vectors

12. Sensitivity to Diabatic Heating Black Filled Squares = GFS BL scheme, GFDL Radiation scheme, Ferrier, SAS on both domains Dark Green Squares= GFS BL scheme, GFDL Radiation scheme, Ferrier, SAS on outer domain. No convection scheme on domain2 Black Open Squares = Knaff and Zehr (2007) Max. Surface Wind speedPressure-Wind Relationship Radius of Maximum Surface Wind Minimum SLP

13. Sensitivity to Diabatic heating: 60-72 hour Azimuthally Averaged Tangential and Radial Wind Speed and Circulation Vectors SAS convection scheme on outer domain, none on domain2 SAS on both domains

14. Black Filled Squares = Ferrier Orange Squares= WSM5 Pink Squares= WSM6 Dark Red Squares= Thompson Black Open Squares = Knaff and Zehr (2007) Max. Surface Wind speedPressure-Wind Relationship Radius of Maximum Surface Wind Boundary Layer Scheme Radiation Scheme Convective Parameterization Scheme GFSGFDLSAS Sensitivity to Diabatic Heating (cont’d) Minimum SLP

15. Ferrier (control) WSM5 WSM6Thompson Sensitivity to Diabatic Heating (cont’d)

16. Summary 1.There is a significant sensitivity of RMW to the size of the initial vortex. 2.RMW’s sensitivity to vertical diffusion is much greater than the horizontal. 3. The slope of RMW is also dependent on the variation in diabatic forcing. 4. Further observational analysis and theoretical understanding are needed to determine an “optimal” operational physics.