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Controlling Factors of the Radius of Maximum Winds in HWRF

This study explores the impact of initial vortex size, diffusion, and diabatic heating on the radius of maximum winds in the HWRF model. Findings suggest significant sensitivity to initial conditions and vertical diffusion. Further research is required for optimal operational physics.

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Controlling Factors of the Radius of Maximum Winds in HWRF

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  1. Controlling Factors of the Radius of Maximum Winds in HWRF 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) Presented at The 65th Interdepartmental Hurricane Conference Miami, FL, 02 March 2011

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

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

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

  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) 9 km Model grid spacing: dx = dy = 0.06, 0.02 (~9 km, ~ 3 km) kx = 43 (NMM sigma-p levels) 3 km 55o 55o

  6. Sensitivity to the size of the initial vortex Minimum SLP Max. Surface Wind speed Pressure-Wind Relationship Radius of Maximum Surface Wind 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)

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

  8. Sensitivity to Horizontal Diffusion Max. Surface Wind Speed Pressure-Wind Relationship Minimum SLP Radius of Maximum Surface Wind 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)

  9. Sensitivity to Horizontal Diffusion: 60-72 hour Azimuthally Averaged Tangential and Radial Wind Speed and Circulation Vectors Default Hor. Diffusion 0.5 × Hor. Diffusion 1.5 × Hor. Diffusion 4.0 × Hor. Diffusion 2.0 × Hor. Diffusion

  10. Sensitivity to Vertical Diffusion Minimum SLP Max. Surface Wind speed Pressure-Wind Relationship Radius of Maximum Surface Wind 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)

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

  12. Sensitivity to Diabatic Heating Max. Surface Wind speed Pressure-Wind Relationship Minimum SLP Radius of Maximum Surface Wind 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)

  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. Sensitivity to Diabatic Heating (cont’d) Minimum SLP Max. Surface Wind speed Pressure-Wind Relationship Radius of Maximum Surface Wind Black Filled Squares = Ferrier Orange Squares= WSM5 Pink Squares= WSM6 Dark Red Squares= Thompson Black Open Squares = Knaff and Zehr (2007)

  15. Sensitivity to Diabatic Heating (cont’d) WSM5 Ferrier (control) WSM6 Thompson

  16. Summary There is a significant sensitivity of RMW to the size of the initial vortex. 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.

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