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

urre

nt v

eloc

ityW

ave-

Indu

ced

stre

ss

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)