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Young C. Kwon, Robert Tuleya, Hua-lu Pan, Vijay Tallaparagada, William Lapenta and Steve Lord

Implementation of New Air-Sea Exchange Coefficients(Cd/Ch) into the Operational HWRF Model: Impact on Hurricane Intensity Forecast Skill. Young C. Kwon, Robert Tuleya, Hua-lu Pan, Vijay Tallaparagada, William Lapenta and Steve Lord (EMC/NCEP/NWS/NOAA). Motivation.

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Young C. Kwon, Robert Tuleya, Hua-lu Pan, Vijay Tallaparagada, William Lapenta and Steve Lord

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  1. Implementation of New Air-Sea Exchange Coefficients(Cd/Ch) into the Operational HWRF Model:Impact on Hurricane Intensity Forecast Skill Young C. Kwon, Robert Tuleya, Hua-lu Pan, Vijay Tallaparagada, William Lapenta and Steve Lord (EMC/NCEP/NWS/NOAA)

  2. Motivation • The HWRF model showed the strong positive intensity bias during the 2008 and 2009 season • Because the main energy source and sink of hurricanes are enthalpy and momentum fluxes from the ocean, sensitivity tests of air-sea exchange coefficients are performed to improve the intensity forecast skill of HWRF by reducing the intensity bias • Test results show that the observation based Cd (Powell 2003) and Ch (CBALST 2007) combination produced the best performance

  3. Cd Profiles vs wind speed operational 2003 Powell Ch Profiles vs wind speed operational CBLAST

  4. Ratio of Ch to Cd for Operational and Modified HWRF Configurations Operational HWRF Modified (test)

  5. Experiment Design Cases: Total of 154 runs Hurricane Fay: 2008.08.15.18 – 2008.08.24.00 (33 runs) Hurricane Gustav: 2008.08.25.12 – 2008.09.01.18 (30 runs) Hurricane Hanna: 2008. 08.28.06 – 2008.09.07.00 (39 run) Hurricane Ike: 2008.09.01.12 – 2008.09.14.06 (52 runs) HWRF Configurations: 1) H48N: Operational HWRF (blue) 2)H5_5: Modified Ch/Cd (purple) Cd: 2003 Powell Ch: CBALST (Jun Zhang et al, 2007)

  6. Avg Intensity Error Reduction of intensity error Max. Improvement: ~ 22% (4.3kt) Avg Track Error No impact on track error

  7. Intensity Bias Reduction in HWRF intensity bias for longer lead time guidance Standard Deviation

  8. Number of superior performance

  9. Intensity Error (IKE) Max. Improvement: ~ 35% (8.0kt) Track Error (IKE)

  10. Fay Intensity Error (FAY) Max. Improvement: ~ 24% Track Error (FAY) Fay

  11. Intensity Bias Standard Deviation

  12. Summary • The observation based Cd and Ch improve the intensity forecast skill of HWRF model about 20% • The positive intensity bias of HWRF reduce about half at the 4-5 day forecast • The track forecast skill remains the same with change of Cd and Ch

  13. Future plan 1. Changing momentum Zo and thermal Zo instead of directly modifying Cd /Ch (Bob Tuleya, Issac Ginis) Zom from wave mode ouput  HWRF surface physics  surface fluxes 2. Conduct experiments to improve the boundary layer physics of HWRF (J. Han GFS physics member)

  14. Coupled-Wave model output Courtesy to Isaac Ginis

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