model vertical coordinates and levels and nesting
DESCRIPTION
Model Vertical Coordinates and Levels and Nesting. Model Vertical Coordinates. Earliest models were in z or p. A problem near terrain (complex boundary conditions where model level intersected mountains) - PowerPoint PPT PresentationTRANSCRIPT
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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
geometries…sigma coordinates. Sigma p and z. Still heavily used today.
• Also used: potential temperature (theta coordinates, eta coordinates—like 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 nesting—running 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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