MOM4: the Ocean Model for CFSRR

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MOM4 the Ocean Model for CFSRR

• Jiande Wang Xingren Wu
• David Behringer and Hua-Lu Pan

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Outline

• Main feature of MOM4
• What we did and doing on MOM4
• Preliminary results from coupled run

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Whats MOM4

• The Modular Ocean Model (MOM4) is a numerical
  representation of the oceans
• hydrostatic primitive equations developed by
  GFDL. It is designed primarily as a tool for
  studying the ocean climate system.

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Release Version of MOM4

• Jan, 2004 MOM4p0a
• Mar, 2004 MOM4p0b
• Aug, 2004 MOM4p0c
• Dec, 2004 MOM4cDec10
• Jun, 2005 MOM4d
• Final version MOM4p0
• this is what we are using now

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Main Feature

• Coded in Fortran90, units are KMS
• Re-engineered Parallel infrastructure (MPI)
• All I/O is handled via NetCDF, will support IEEE
  format output in the future.
• Only contains one cpp-preprocessor option
  (ifdefs), (MOM3 has 300-400 ifdefs).
• Upside clean up the logic in the separate
  modules, code more readable, short compiling
  time.
• Downside increase code maintenance. System
  structure becomes complicated (80 directories).
• 2D horizontal domain decomposition. No memory
  windows or slabs. Increase computation efficiency.

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Numerical/dynamic characteristics

• Generalized orthogonal horizontal coordinator.
  Support both standard spherical coordinator and
  tripolar grid (no polar filter required, full
  Arctic Ocean).
• Z-coordinator vertically. Only support B-grid
  currently.
• Partical cell for bottom topography
• Non-Boussinesq explicit free surface (Greatbatch
  et al. 2002).
• explicit fresh water flux
• McDougall et al. (2003) equation of state with in
  situ density a function of local potential
  temperature, salinity and hydrostatic pressure.
• Various kind of tracer advection schemes.
• KPP vertical mixing (Large et al. 1994)
• Chlorophyll based shortwave penetration (Morel
  and Antoine, 1994)
• runoff process

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SeaWiFS Chlorophyll (Sweeney et al. 2005)
Note the large value near coasts and equatorial
pacific and Atlantic which are associated with
high level of biological activity
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Impact of runoff from Amazon on sea surface
salinity
MOM3
MOM4
Including of runoff process revealed detail
structure of salinity near the river mouth
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Model configuration

• Horizontal resolution
• (1). 1 degree zonally, 1/3 degree in tropics,
  gradually increasing meridionally to 1 degree 30N
  and 30S.
• (2). 0.5 degree zonally, 1/4 degree in tropics,
  gradually increasing meridionally to 0.5 degree
  30N and 30S
• Vertical resolution
• 40 layers, 10 meters depth in the up 200
  meters.

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What we did and doing with MOM4

• Simple test (platform compatibility and
  reproductively)
• Ocean only forced by R2
• OceanIce forced by R2
• Ocean data assimilation (Dave Behringer)
• OceanIceGFS coupled model

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Results from coupled run SST
Less than 1 degree of SST bias in most of
tropical region
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Seasonal cycle of SST
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GODAS
Depth
MOM4
MOM4-GODAS
Small temperature bias in equatorial Pacific
region
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MOM4
OISST
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Summary

• MOM4 has been tested in EMC climate group as a
  component for the coupled system with encouraging
  results.