1. Coupled Atmosphere-Wave-Ocean Modeling
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. Param. of wave dissipation
ATMOS. MODEL
(MM5/COAMPS/WRF)
OCEAN MODEL
(HYCOM/3DPWP/ROMS)
WAVE MODEL
(WAVEWATCH III/WAM)
Roughness length
Wind-induced stress
Surface fluxes
SST
SSH & current velocity
Wave-Induced stress
Coupled Atmosphere-Wave-Ocean Modeling System for Hurricane Predictions
LES
Sea
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?

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: Others:
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,
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,
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,
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,

7. Conclusions and Challenges
Accurate 2-D wave spectra, fully coupled to atmosphere and ocean, is a key.
Ck/CD varies spatially in hurricanes, (actual wind) or (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. Coupled Atmosphere-Wave-Ocean Modeling
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)
RSMAS/UM real-time model forecasts of rainrate (mm/h, top-left), surface wind speed (m/s, bottom left, two highlighted contours are tropical storm and hurricane strength wind speeds), significant wave height (m, bottom right), and NDBC buoy observed (black) and model forecasted (red) SWH/wave period/wind (top-right) in Hurricane Katrina from 0000 UTC 27 Aug – 0000 UTC 30 Aug For more information, contact Shuyi Chen at RSMAS/UM