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

Evaluation and Improvement of Ocean Model Parameterizations for NCEP Operations
Lynn K. Shay 1 , George. R. Halliwell, Jr. 2 , Benjamin Jaimes 1
(nshay@rsmas.miami.edu)
1 Division of Meteorology and Physical Oceanography, RSMAS, University of Miami
2 NOAA/AOML/POD
The research focused on testing model initialization schemes primarily in the Gulf of Mexico
(GOM) and processing data required for model evaluation. This dataset includes in situ Naval
Research Laboratory Acoustic Doppler Current Profiler (ADCP) data from Ivan and during
Katrina and Rita (courtesy of Minerals Management Service) as well as measurements acquired
during NOAA Hurricane Research Division Intensity Fluctuation Experiments (IFEX) in pre and
post Rita in 2005, and during Gustav and Ike (2008). All of these hurricanes have been shown to
have been affected by warm and cold ocean features in the GOM. Numerical experiments for the
Ivan case demonstrated the import of model sensitivity to vertical resolution, horizontal
resolution, vertical mixing, air-sea flux parameterizations (drag coefficients), ocean dynamics,
and the accuracy of the ocean initialization.
Analyses of the ocean response to hurricanes Katrina and Rita from in-situ (moorings, airborne
profilers) and satellite-based measurements have shown significant modulation of the oceanic
mixed layer cooling by the geostrophically balanced currents in both warm and cold eddies.
Using an idealized, isopycnic ocean model and wind fields derived from data acquired during
hurricane Katrina, aspects of the ocean response to tropical cyclones (TC) are investigated in the
eddies. It is found that rather than a function of the wind stress curl, the upwelling response is a
function of the curl of wind-driven acceleration of oceanic mixed layer (OML) geostrophic
currents: upwelling (downwelling) regimes prevail under the TC’s eye over cyclonic
(anticyclonic) eddies. Predominant isotherm downwelling, wind erosion over deep, warm, and
nearly homogeneous water columns, and dispersion of OML near-inertial energy only produce
OML cooling of ~1 o C in anticyclones, consistent with observations. By contrast, widespread
upwelling of the isotherms and wind-induced mixing over shallow OMLs with enhanced vertical
current shears produce OML cooling of ~4 o C in cyclones. For oceanic models to correctly
reproduce TC-induced OML cooling and feedback mechanisms to TC intensity, they must
accurately resolve mesoscale oceanic features, including position and thermal, density, and
velocity structures.
For this reason, ocean model improvement efforts at the National Centers must focus on
improving the model initialization through assimilation methods. During the summer of 2010,
an extensive data set was acquired in response to the Deep Water Horizon oil spill in the Gulf of
Mexico. The 3-dimensional snapshots from NOAA research aircraft of the upper ocean structure
captured the complex detachment/reattachment processes associated with Eddy Franklin from
the Loop Current.
Session 5 – Page 7