EVALUATION OF UPPER OCEAN MIXING PARAMETERIZATIONS

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EVALUATION OF UPPER OCEAN MIXING PARAMETERIZATIONS

• S. Daniel Jacob1, Lynn K. Shay2 and George R.
  Halliwell2

1 GEST, UMBC/ NASA GSFC, Greenbelt, MD 20771 2
MPO, RSMAS, University of Miami, Miami, FL 33149
Alan Wallcraft (NRL Stennis) Chet Koblinsky (NOAA)
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Importance of Ocean Mixing

• Based on Observational Analysis (Jacob et al.,
  JPO 2000)
• Entrainment is the dominant mechanism in
  controlling mixed layer budgets.
• Mixed layer heat and mass budgets strongly depend
  upon the entrainment scheme used crucial for
  intensity prediction.
• Numerical Modeling (Jacob and Shay, JPO, 2003)
• Measured and simulated quantities based on
  different hypothesis are used to compute
  entrainment mixing.
• Bulk schemes in MICOM also indicated strong flux
  variability.

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Motivation HYbrid Coordinate Ocean Model (HYCOM)
Results
(Bleck 2002, Halliwell 2004)

• Configuration
• Domain Gulf of Mexico
• Resolution 0.07?
• 50 Levels/ Layers
• Closed Boundaries
• Initial Conditions
• Quiescent Conditions with Gilbert forcing
• SST Variability
• Significant in the directly forced region
• Large range in fluxes
• Sensitivity to precipitation

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Hycom Q Movie
Gaspar
KPP
MY2.5
PWP
5
2 Rmax
No Precip
Precip
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Objectives

• Evaluate and Validate Mixing Schemes to identify
  the most appropriate parameterizations for use in
  coupled prediction model.
• Schemes in the Hybrid Coordinate Ocean Model
• K Profile Parameterization (Large et al. 1994
  KPP)
• Gaspar (1988)
• Price et al. (1986 PWP) scheme.
• Mellor and Yamada (1974 MY2.5) Level 2.5 K-e
  scheme
• Canuto et al. (2001, 2002 GISS)
• Compare Simulations to Observations
• Gilbert (1988)
• Isidore (2002)
• Lili (2002)

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Project Schedule

• Model Configuration, set up, derivation of
  initial conditions and forcing February 2004.
• Gilbert simulations and comparison May 2004
• Isidore and Lili Simulations and comparison to
  observations Jan 2005
• Recommendation of the most appropriate mixing
  scheme for use in coupled prediction models. Aug
  2005.

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Model Configurations

• Gilbert (1988)
• Prior HYCOM/ MICOM configuration on Mercator grid
  at 0.07 resolution at the equator.
• Buffer zones at open boundaries relaxed to
  climatology.
• Simulations from 14 Sep 1988 to 20 Sep 1988.
• Isidore (2002) and Lili (2002)
• Domain includes Caribbean Sea and the Gulf of
  Mexico.
• Treated as a single case with 20 day integration
  for each mixing parameterization.
• Configured as a nest of the basin scale HYCOM
  that provides conditions at the open boundaries.

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Gilbert Initial Conditions

• Pre-storm variability due to a Loop Current Warm
  Core Eddy (LCWCE) Eddy F
• Sampled extensively by Minerals Management
  Service - Yearday 200/300 data.
• Propagated westward at 3 to 4 km/day (Average
  translation speed 5 km/day for Gulf eddies
  Vukovich and Crissman 1986).
• Possess distinct T-S relationship corresponding
  to the subtropical water mass. Shay et al.
  (1998) derived the T-S relationship for the Gulf
  Common Water and the Loop Current Eddy Water
  using historical and Yearday 200/300 data set.
• Realistic initial conditions are derived by
  combining the objectively analyzed day 200 data
  with the Levitus climatology.

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Temperature-Salinity Diagram
LCW
GCW
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Pre-Gilbert Sea Surface Height

• HYCOM is initialized following the methodology
  used by Jacob and Shay (2003).
• Location of pre-storm eddy (LCWCE F) is
  accurately reproduced.
• Depth of 26 C and 20 C isotherms compare well
  to observations.

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Isidore Initial Conditions

• Pre-storm variability due to the Loop Current in
  the Eastern Gulf of Mexico.
• As the source of eddies, the Loop Current Water
  possess the same distinct T-S relationship
  corresponding to the subtropical water mass.
• Realistic initial conditions from the 0.08 North
  Atlantic HYCOM. Courtesy of the Data Assimilative
  Ocean Modeling NOPP project of RSMAS, University
  of Miami and Naval Research Lab, Stennis Space
  Center.
• The location of boundary currents and eddies are
  reproduced accurately by the basin-scale nowcast/
  forecast system.
• Fields evaluated with respect to expendable probe
  data.

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Hycom Nowcast/Forecast System
(Smedstad et al. 2003)

• North Atlantic Hycom at 0.08 resolution
  extending from 28 S to 70 N. 26 levels/ layers
  in the vertical. High resolution surface forcing
  from FNMOC with Salinity relaxation at the
  surface. 3 buffer zones in the north and south
  relaxed to climatology.
• Satellite altimeter height anomalies from the
  MODAS operational system at NAVOCEANO.
• Mean Sea Surface Height from the 0.08 Atlantic
  MICOM.
• Vertical projection of surface height signature
  using the Cooper-Haines (1996) technique.
• Sea Surface Temperature not assimilated at
  present.

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Pre-Isidore Sea Surface Height 19 Sept 2002

• Pre-storm mesoscale variability is accurately
  reproduced in terms of simulated SSH.
• Corresponds to 19 Sept 2002 pre-storm experiment.

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Sea Surface Height Anomaly and Ocean Heat Content
19 Sept 2002
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Pre-Isidore Sea Surface Temp 19 Sept 2002

• Pre-storm sea surface temperatures in the
  assimilated fields are biased lower throughout
  the domain with 0.5 C in the Caribbean Sea and
  slightly higher elsewhere.

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Meridional Cross Section along 84 W
The depth of 26 and 20 C isotherms compare well
to profiler data in the Caribbean Sea.
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Meridional Cross Section along 86 W
Due to the lower SSTs, the depth of 26 and 20 C
isotherms are shallower compared to profiler data
by 10 m on the average in the central gulf of
Mexico.
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Zonal Cross Section along 24 N
The model captures subsurface structure
variability due to assimilated altimetric heights
well.
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Wind Forcing

• Gilbert (1988)
• Flight level reduced winds and buoy data in the
  core.
• ECMWF 6 hourly surface data provides large scale
  field.
• Combined using NOAA Hurricane Research Division
  HWIND program to produce wind forcing every 3
  hours.
• Constant air temperature and relative humidity
  with synthetic rain rates derived from wind field
  distribution.
• Isidore (2002) and Lili (2002)
• Flight level reduced winds and buoy data analyzed
  using HWIND available on regular grid (courtesy
  Dr. Mark Powell).
• FNMOC surface forcing provides the large scale
  forcing.
• Blended using the parameter matrix objective
  analysis technique of Mariano and Brown (1992)
  with cubic splines every 3 hours.

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Gilbert Wind Field Structure 16 Sep 88 06UTC
The double eyewall structure is captured
accurately by the analysis
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Lili Wind Field Structure 02 Oct 02 00UTC
The parameter matrix algorithm works well in
blending the large scale data with the HWIND
analysis.
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Summary and Future Work

• Initial Conditions and forcing are established to
  investigate the sensitivity of mixing
  parameterizations in upper ocean heat content
  simulations.
• While the Gilbert initial conditions compare well
  with pre-storm observations, the SST prior to
  Isidore is biased low in the model by an RMS
  difference of 1.1 C in the domain. Updated
  fields where SSTs are assimilated will fix this
  problem for the Isidore and Lili cases. With a
  RMS differences of about about 0.2 m/s, simulated
  current field compares well with profiler data.
  Detailed comparisons are in progress to validate
  the initial fields.
• The parameter matrix based objective analysis
  technique works well to blend the wind analysis
  data with large scale model fields. This will be
  further improved during the course of the
  project.
• The upper ocean response during hurricane Gilbert
  will be performed in the next phase followed by
  Isidore and Lili simulations.