03-ginis ihc 2012
TRANSCRIPT
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Advancing NOAA’s HWRF prediction systemthrough enhanced physics of the air-sea coupling
and ocean model initialization
Isaac Ginis
B. Thomas, R. Yablonsky, T. Hara, B. Reichl, C. Hughes
University of Rhode IslandV. Tallapragada, H. Tolman (NOAA/NCEP)
J.-W. Bao, C. Fairall, L. Bianco (NOAA/ESRL)R. Tuleya (ODU)
Interdepartmental Hurricane Conference, March 2012
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• HWRF fully coupled Atmosphere-Ocean-Wave
system will include:
– a triple-nested (27/9/3km) HWRF atmospheric model,
– POM or HYCOM ocean model, and
– a multi-grid WAVEWATCH III wave model.
HWRF Coupled Model Structure
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Air-Sea Interface Module
Image courtesy of Fabrice Veron
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• Sea state (wave) dependent drag coefficient
• Wave-induced Stokes drift and upper ocean
mixing
• Wave-induced Coriolis-Stokes effect
• Princeton Ocean Model initialization upgrade
Discussion Outline
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• In the air-sea interface module, the momentum flux(drag coefficient) is calculated using the wave modeloutput and a wave-boundary layer model.
• We have examined two momentum flux models,developed at University of Rhode Island (URI) and
University of Miami (UM) as potential candidates forthe air-sea interface module.
Sea State Dependent
Drag Coefficient
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Evaluation of Wave Spectrum in WW3 and itsImpact on Drag Coefficient in the URI flux model
resolvedparameterized
New tail
H i I (2004) Si l i i h
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Hurricane Ivan (2004) Simulation with
WAVEWATCH and H*Wind Forcing
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Sea-State Dependent Drag Coefficient
WW3 Tail
New Tail
Only data for U10 > 20 m/s are shown
D C ffi i t d
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Drag Coefficient and
Wind Stress - Wind Misalignment
Only data for U10 > 20 m/s are shown
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Stokes Drift Due to Surface WavesUnder Hurricane Conditions
• Surface wave motions introduce net masstransport, “Stokes drift”, which has the effect oftilting and organizing the upper ocean turbulenteddies. The resulting turbulence is called
“Langmuir turbulence”.
• In hurricanes, of particular interest is the
conditions in which wind is misaligned with wavesat angles greater than 90o. In such cases theStokes drift may suppress Langmuir turbulenceand consequent sea surface cooling.
Mi d L Ki ti E
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Mixed Layer Kinetic EnergyMeasurements in Hurricanes
Courtesy of Eric D’Asaro
Lagrangian floats deployed ahead of Hurricane Gustav (2008)found reduced vertical kinetic energy in the mixed layer behindthe storm.
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Stokes Drift Calculations in IdealizedHurricane
• We examine the vertical profile of Stokes driftunder idealized hurricanes.
• WAVEWATCH is used to calculate directional
wavenumber spectra under stationary andtranslating hurricanes (at 5 ms-1 and 10 ms-1),with a Rm=70 km and Vm=45 ms-1.
• Stokes drift is calculated from the surface downto 240 m depth.
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Angle difference between wind direction
and Stokes drift direction at z=k peak-1
Angle exceeds90o behind atranslatinghurricane.
UT=0 UT=5 m/s
UT=10 m/s
km km
km
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Coriolis–Stokes Effect
Figure from Polton et al. (2005)
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surface boundary condition is modified:
Ocean Momentum Equations and
Coriolis–Stokes Forcing
Coriolis-StokesForcing
Wave effect onmomentum flux (Fanet al., 2010) already
included in ASIM
Momentum fluxinto the ocean ≠
wind stress!
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UT=5 m/s UT=10 m/s
Coriolis–Stokes Forcing UnderIdealized Moving Hurricane
Only data for U10 > 20 m/s are shown
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UT=5 m/s UT=10 m/s
Coriolis–Stokes/Wind Stress RatioUnder Idealized Moving Hurricane
Only data for U10 > 20 m/s are shown
P i t O M d l
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Princeton Ocean ModelInitialization Upgrade
• POM is the ocean component of the GFDL,GFDN, HWRF operational models
• It is initialized differently in different oceanbasins:
– Atlantic: GDEM climatology, feature-basedinitialization
– Eastern Pacific: GDEM monthly climatology in GFDLand HWRF, but NCODA in GFDN
– Western Pacific and other ocean basins: NCODA inGFDN
NCEP’ RTOFS ( ti l i 10 25 2011)
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http://polar.ncep.noaa.gov/global/
NCEP’s RTOFS (operational since 10.25.2011)based on 1/12o Global HYCOM
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2011 Atlantic Hurricane Season
http://www.nhc.noaa.gov/2011atlan.shtml
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10/25/11: RTOFS-Global vs. Feature-based
SST
75-m T
RTOFS-Global Feature-based w/GFS SST
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10/25/11: RTOFS-Global vs. Feature-based
Cross-section
SSH
RTOFS-Global Feature-based w/ GFS SST
S
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Summary
• In the process of developing of the Air-Sea
Interface Module for HWRF we examined – 1) sea state dependent momentum flux,
– 2) Stokes drift effect on upper-ocean mixing, and
– 3) Coriolis-Stokes forcing
• Modeling results suggest that behind thehurricane the Stokes drift may suppress
Langmuir turbulence and consequent seasurface cooling.
S
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Summary
• Coriolis-Stokes forcing may reduce momentum
flux into the ocean by 15% of the wind stressnear the radius of maximum wind and to theright of the hurricane center.
• Plans for 2012:
– Implement the air-sea interface module (ASIM) intothe coupled HWRF-WAVEWATCH-POM/HYCOMsystem. Insure that all components of ASIM aremodular and can be transitioned to other TC coupledmodels, including COAMPS-TC.
– Test the ocean model initialization in GFDL/POM andHWRF/POM based Global RTOFS.
Ocean Observations Needed for
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Ocean Observations Needed forCoupled Atmosphere-Wave-Ocean
Model Evaluations
• Directional wave spectra (to be available fromWSRA measurements)
• Temperature and current measurements withinthe hurricane core regions. Only a few available
in the Atlantic.