CBLAST-Hurricane Coupled Atmosphere-Wave-Ocean Modeling
Specific Objectives:
• Wind-Wave Coupling
• Effects of Sea Spray
• Atmosphere-Ocean Coupling
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.
Tools for hurricane research during the CBLAST (Coupled Boundary Layers Air-Sea Transfer) experiment
ATMOS. MODEL
(MM5/COAMPS/WRF)
OCEAN MODEL(HYCOM/3DPWP/ROMS)
WAVE MODEL
(WAVEWATCH III/WAM)
Roughness length
Wind-induced stress
Surface fluxes
SST
SSH
& c
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Indu
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Coupled Atmosphere-Wave-Ocean Modeling System for Hurricane Predictions
LESSea
Spray
Param. of spectral tail and drag coefficient
Param. of wave
dissipation
Source function?Drop size distribution?Effects on turbulence?
How do these affect exchange coefficients? What is the ratio of Ck and CD?
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
Obs
Model
Model
Obs
Hurricane Frances (2004)
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.
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
Future ResearchCoupled 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
Significant Wave Height (m)
Model Forecast of Hurricane Katrina (2005) (water depth)
RainRate
Surface Wind Speed (m/s)