CBLAST-Hurricane Coupled Atmosphere-Wave-Ocean Modeling

1. CBLAST-Hurricane Coupled Atmosphere-Wave-Ocean Modeling • A goal of CBLAST is to better understand how hurricanes interact with the ocean, and to use this to improve hurricane forecast models. • Through CBLAST we have improved our knowledge about the processes which fuel hurricanes (heat from the ocean), as well as the frictional forces (drag on the sea surface) which mix the ocean and result in extreme ocean waves. • Specific Objectives: • Wind-Wave Coupling • Effects of Sea Spray • Atmosphere-Ocean Coupling

2. Tools for hurricane research during the CBLAST (Coupled Boundary Layers Air-Sea Transfer) experiment

3. Coupled Atmosphere-Wave-Ocean Modeling System for Hurricane Predictions ATMOS. MODEL (MM5/COAMPS/WRF) OCEAN MODEL (HYCOM/3DPWP/ROMS) Surface fluxes SST Param. of wave dissipation LES Sea Spray SSH & current velocity Wind-induced stress Wave-Induced stress Roughness length WAVE MODEL (WAVEWATCH III/WAM) Param. of spectral tail and drag coefficient Source function? Drop size distribution? Effects on turbulence? How do these affect exchange coefficients? What is the ratio of Ck and CD?

4. Research Progress • Wind-Wave Coupling Parameterization • Fully coupled atmosphere-wave-ocean model simulations of hurricanes (e.g., Bonnie, Floyd, Lili, Fabian, Isabel, Frances, Katrina) and comparisons with CBLAST observations • Publications

5. Hurricane Frances (2004) Model Obs Model Obs

6. Recent Publications BAMS issue on CBLAST: Chen, S. S., J.F. Price, W. Zhao, M.A. Donelan, E.J. Walsh, 2007: The CBLAST-Hurricane Program and the next-generation fully coupled atmosphere-wave-ocean models for hurricane research and prediction. BAMS, 311-317. Black, P.G., E.A. D’Asaro, W.M. Drennan, J.R. French, P.P. Niiler, T.B. Sanford, E. Terrill5, E.J. Walsh and J. Zhang, 2007: Air-Sea Exchange in Hurricanes: Synthesis of Observations from the Coupled Boundary Layer Air-Sea Transfer Experiment, BAMS, 357-374. Edson, J., T. Crawford, J. Crescenti, T. Farrar, J. French, N. Frew, G. Gerbi, C. Helmis, T. Hristov, D. Khelif, A. Jessup, H. Jonsson, M. Li, L. Mahrt, W. McGillis, A. Plueddemann, L. Shen, E. Skyllingstad, T. Stanton, P. Sullivan, J. Sun, J. Trowbridge, D. Vickers, S. Wang, Q. Wang, R. Weller, J. Wilkin, D. Yu, and C. Zappa, 2007: The Coupled Boundary Layers and Air-Sea Transfer Experiment in Low Winds (CBLAST-LOW). BAMS, in press. Others: Houze, R. A., S. S. Chen, B. Smull, W.-C. Lee, M. Bell, 2007: Hurricane intensity and eyewall replacement. Science, 315, 1235-1239. Chen, S. S., J. Knaff, F. D. Marks, 2006: Effect of vertical wind shear and storm motion on tropical cyclone rainfall asymmetry deduced from TRMM. Mon. Wea. Rev., 134, 3190-3208.

7. Conclusions and Challenges • Accurate 2-D wave spectra, fully coupled to atmosphere and ocean, is a key. • Ck/CD varies spatially in hurricanes, 0.4-0.8 (actual wind) or 0.6-1.0 (gradient wind, which is similar to Emanuel 1995 in a storm-average). • CD and Ck for U10 > 30 m/s • Wave-breaking and sea-spray remains to be an unresolved issue and need to be further examined in the coupled model (e.g., link to 2-D spectra and breaking parameters, etc.). • Better understanding of the physical processes • Accurate surface flux (especially enthalpy flux) and PBL measurements to evaluate model results and improve model parameterizations • Lack of good model initial conditions • Need robust and efficient data assimilation system

8. Future Research Coupled Atmosphere-Wave-Ocean Modeling • Exploring various data assimilation (e.g., hybrid EnKF and 4DVar) for the coupled models • Improving sea spray parameterization with explicit link to surface waves (e.g., 2D spectra and breaking parameters) • Implementing and testing the coupled parameterizations in COAMPS and WRF

9. Model Forecast of Hurricane Katrina (2005) (water depth) RainRate Surface Wind Speed (m/s) Significant Wave Height (m)