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

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

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?

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

Hurricane Frances (2004) Model Obs Model Obs

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, 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

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

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 2005. For more information, contact Shuyi Chen at RSMAS/UM (schen@rsmas.miami.edu).