Model Vertical Coordinates and Levels and Nesting

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Model Vertical Coordinates and Levels and Nesting
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Model Vertical Coordinates

• Earliest models were in z or p.
• A problem near terrain (complex boundary
  conditions where model level intersected
  mountains)
• Next innovation were terrain-following
  geometriessigma coordinates. Sigma p and z.
  Still heavily used today.
• Also used potential temperature (theta
  coordinates, eta coordinateslike p) and hybrids
  (such as sigma-p/theta)

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Model Levels

• Modern models generally have been 35 and 100
  levels.
• Generally NOT uniform in height.
• Virtually all have many model levels near the
  surface to define the PBL.
• Many have higher density of levels near the
  tropopause as well.

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ECMWF Levels
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Nesting

• If one has lots of computer power and a global
  model, no worry about horizontal boundary
  conditions or nesting
• But if want to run at high resolution over a
  limited domain, can use nestingrunning a
  separate model domain at high resolution embedded
  in a lower-resolution simulation.
• Can have one way or two way nesting.

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Next Generation Models May Not Have Separate Nests
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Problem What kind of physics parameterization
can handle multiple resolutions at SAME TIME?
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