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Jian-Wen Bao Christopher W. Fairall Sara A. Michelson Laura Bianco

Evaluation and Improvement of Spray-Modified Air-Sea Enthalpy and Momentum Flux Parameterizations for Operational Hurricane Prediction. Jian-Wen Bao Christopher W. Fairall Sara A. Michelson Laura Bianco NOAA/ESRL/physical Sciences Division

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Jian-Wen Bao Christopher W. Fairall Sara A. Michelson Laura Bianco

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  1. Evaluation and Improvement of Spray-Modified Air-Sea Enthalpy and Momentum Flux Parameterizations for Operational Hurricane Prediction Jian-Wen Bao Christopher W. Fairall Sara A. Michelson Laura Bianco NOAA/ESRL/physical Sciences Division (in collaboration with Naomi Surgi and Young Kwon of NCEP/EMC) Presented at: The 62nd Interdepartmental Hurricane Conference Charleston, SC: March 5, 2008

  2. OUTLINE • Parameterization of sea-spray mediated sensible and latent heat fluxes • Parameterization of sea-spray modification of momentum flux • Implementation andtesting of the ESRL sea-spray scheme in the HWRF model • Summary and Preliminary Conclusions

  3. Parameterization of Sea Spray: Wind Speed DrivenFairall/Andreas/Kepert Early 1990’s Raw Direct sensible Raw Direct Latent Raw Droplet Sensible Raw Droplet Latent Net fluxes emerging from top of droplet layer Alpha accounts for SUBGRID feedback (droplet – T/q profile interactions)

  4. Feedback The thermal feedback is defined by distortions of the temperature and humidity profiles in the droplet –filled surface layer: δT and δq, which are determined by the source strength and residence time.

  5. Parameterization of the Sea-Spray Modification of Momentum Flux (e.g., Barenblatt 1996 and Lykossov 2001) where S is the spray concentration profile. Where the mean fall speed of droplets spray generation height empirical parameter

  6. Impact on the Exchange Coefficients

  7. Implementation in the HWRF model The subroutine of the NOAA/ESRL sea-spray parameterization is called by (and appended to the end of) module_bl_gfs.F A function routine (function qsat_spray) is added to module_gfs_funcphys.F Testing experiments have been conducted on Haze with Katrina (2005), Rita (2005), Emily (2005), Dennis (2005) and Helene (2006).

  8. max. wind speed min. sea-level pressure track Test with Katrina (2005)initial time: 0000 UTC 27 August 2005

  9. Test with Katrina (2005) control thermal thermal + momentum Valid at 0060 UTC 29 Aug 2005

  10. Test with Katrina (2005) thermal control thermal + momentum Valid at 0060 UTC 29 Aug 2005

  11. Summary and Conclusions • The impact of the sea-spray parameterization on the track forecast is negligible, despite the noticeable impact on the intensity. • Both the intensity and structure are influenced by the parameterized thermal and kinematic effects of sea spray. • The response of the storm intensity does not appear to be proportional to the change in the droplet source strength and feedback strength. • The errors in the HWRF model forecast can only be partially • attributed to the errors in the surface fluxes. • The performance of the sea-spray parameterization scheme in the HWRF model needs to be further evaluated and calibrated.

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