65th IHC Booklet/Program (pdf - 4.9MB) - Office of the Federal ...

Sensitivities of air-ocean-wave coupling on the prediction of Hurricanes Frances and Ivan
Sue Chen 1 , Travis Smith 2 , Saša Gaberšek 1 , Tim Campbell 2 , Shouping Wang 1 , James Doyle 1 , and
Rick Allard 2
1 Marine Science Division, Monterey
2 Oceanography Division, Stennis
Naval Research Laboratory
A series of model runs were conducted to exam the sensitivities of air-ocean-wave coupling on
the intensity and structure change of hurricanes Frances and Ivan as well as the associated ocean
and wave response. The hurricane model used for this study is the newly developed six-way airocean-wave
fully coupled COAMPS-TC. The coupling is achieved using the Earth System
Modeling Framework to couple the COAMPS-TC with the Navy Coastal Ocean Model (NCOM)
and Simulating WAves Nearshore (SWAN). Special in situ measurements of atmosphere, ocean,
and wave during the Coupled Boundary Layer Air-Sea Transfer Experiment (CBLAS) field
campaign sponsored by the Office of Naval Research were used to validate the model results.
For the simulations of Hurricane Frances, it is found using a higher resolution ocean grid
improved the magnitude of the trailing cold sea surface temperature anomaly forced by the
hurricane. The forecast sea temperature bias below the ocean mixed layer was further reduced
when the high-resolution ocean model initial condition was improved using the ocean data
assimilation in the ocean spin-up period. In addition, the significant wave height bias was
reduced if using the level-off wind stress value from CBLAS instead of the original generation 3
wind source term in SWAN. Including the wave feedback to the atmosphere also produced a
much higher value of momentum drag near the eyewall region. The overall intensity and track
forecast differences between the uncoupled and various coupled runs (one to six-way coupling)
were found to be as large as 18 m/s and 10 nautical miles, respectively.
For the hurricane Ivan study, a special ADCP data array collected by NRL is also used to
evaluate the shallow and deep water current response. Including the wave Stokes’s drift, wave
radiation stress, and wave bottom stress feedback improved the complex correlation coefficients
and mean directional error for the ocean current. The wave spectrum comparison between
SWAN and Scanning Radar Altimeter showed SWAN generated too much energy in long waves
which in turns produced a larger significant wave height bias. These preliminary results indicate
a more consistent treatment of momentum stress, sensible heat flux, and latent heat flux at the
air-sea interface may be needed in order to improve the forecast of the hurricane environment.
The development of a new unified air-sea interface module jointly with NOAA, University of
Miami, and University of Rhode Island founded by National Oceanographic Partnership Program
is discussed.
Poster Session – Page 12