George Halliwell, Nick Shay

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Evaluation of the Simulated Ocean Response to
Hurricane Ivan in Comparison to High-Quality
Ocean Observations

• George Halliwell, Nick Shay
• Rosenstiel School of Marine and Atmospheric
  Science
• University of Miami, Miami, FL
• William Teague
• Naval Research Laboratory, Stennis Space Center,
  MS

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GOALS

• Improve ocean model response to TC forcing in a
  complex oceanographic environment
• Improve coupled TC prediction models
• Especially intensity forecasts
• Improve hindcasts of the ocean response during
  and after individual storms
• e.g., oil and gas industry
• Improve our scientific understanding of the ocean
  response to TC forcing

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Ocean Model Improvement

• Ocean models still require evaluation and
  improvement of TC response
• Requires high-quality observations
• Requirements
• Accurate initialization
• Ocean features (currents, warm- and cold-core
  eddies)
• Vertical T, S, density structure
• Ocean Heat Content (OHC) distribution
• Improve air-sea flux parameterizations
• Improve vertical mixing

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APPROACH

• Evaluate HYbrid Coordinate Ocean Model (HYCOM)
  against high-quality ocean observations
• Future ocean component of HWRF model
• Uncoupled ocean response simulations
• Isolate ocean model sensitivity given constant
  forcing
• Will complement evaluation of the coupled HWRF
  model
• Initial Focus - Hurricane Ivan (Sept. 2004)
• Initial OHC distribution important to SST
  response
• High-quality ADCP velocity moorings
• Naval Research Laboratory SEED project

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Observed SST Response to Ivan
Microwave satellite (Remote Sensing Systems)
AVHRR (Walker et al, 2005)
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Ivan Intensity
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Hurricane Ivan Simulations (1)

• Gulf of Mexico domain
• 10 Sept. to 6 Oct. 2004
• Initial and boundary conditions
• Ocean nowcast-forecast system
• Alternative to feature-based analysis
• Several products available or under development
• Global Ocean Data Assimilation Experiment (GODAE)
• Test the U. S. Navy system
• Under development by NOPP consortium
• Couples HYCOM to the NCODA assimilation system

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Hurricane Ivan Simulations (2)

• Forcing
• Navy 0.5-degree NOGAPS atmospheric model
• Wind speed blended with higher resolution fields
  obtained from the NOAA/HRD HWIND product
• Wind stress calculated using Powell cd

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Ivan Analysis

• Importance of accurate initialization
• Evaluate ocean data assimilative hindcast
• U.S. Navy ocean nowcast-forecast system
  (HYCOM-NCODA)
• Sensitivity to vertical mixing parameterization
• K-Profile Parameterization (KPP)
• Mellor-Yamada level 2.5 closure (MY)
• Goddard Institute for Space Studies (GISS)
• Ocean current response
• ADCP moorings in north-central Gulf of Mexico

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SSH, 10 Sept. 2004
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Simulated SST Response to Ivan
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SST (C) Before and After Ivan
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Depth-Time Temperature Variability
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Ivan Analysis

• Importance of accurate initialization
• Evaluate ocean data assimilative hindcast
• U.S. Navy ocean nowcast-forecast system
  (HYCOM-NCODA)
• Sensitivity to vertical mixing parameterization
• K-Profile Parameterization (KPP)
• Mellor-Yamada level 2.5 closure (MY)
• Goddard Institute for Space Studies (GISS)
• Ocean current response
• ADCP moorings in north-central Gulf of Mexico

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SST Change, 10 to 17 Sept.
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SST (C) After Ivan
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Ivan Analysis

• Importance of accurate initialization
• Evaluate ocean data assimilative hindcast
• U.S. Navy ocean nowcast-forecast system
  (HYCOM-NCODA)
• Sensitivity to vertical mixing parameterization
• K-Profile Parameterization (KPP)
• Mellor-Yamada level 2.5 closure (MY)
• Goddard Institute for Space Studies (GISS)
• Ocean current response
• ADCP moorings in north-central Gulf of Mexico

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SEED Moorings and Ivan Path
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Summary

• Accurate initialization of the Loop Current,
  detached warm eddy, and two cold eddies by an
  ocean nowcast product was critically important to
  the Ivan ocean response simulations
• Cannot forget cold ocean features
• Response is sensitive to vertical mixing
  parameterization
• Three-dimensional dynamical processes are
  important
• Good qualitative comparison between observed and
  simulated currents at SEED moorings
• Simulated near-inertial currents decay too
  rapidly
• Ocean model improvement will require high-quality
  three-dimensional ocean observations