[CF-metadata] hybrid height

Jonathan Gregory j.m.gregory at reading.ac.uk
Sun Nov 13 13:50:24 MST 2005

Dear All

I believe that the current definition of the atmosphere hybrid height
coordinate in CF Appendix D is incorrect. To match what is used in the HadGEM1
model, the definition should be as below. Is anyone using the definition
which currently appears in the standard? If not I propose we should replace it.



standard_name = "atmosphere_hybrid_height_coordinate"


z(n,k,j,i) = a(k) + b(k)*orog(n,j,i)

where z(n,k,j,i) is the height above the geoid (approximately mean sea level)
at gridpoint (k,j,i) and time (n), orog(n,j,i) is the height of the surface
above the geoid at (j,i) and time (n), and a(k) and b(k) are the coordinates
which define hybrid height level k. a(k) has the dimensions of height and b(k)
is dimensionless.

The format for the formula_terms attribute is

formula_terms = "tau: var1 eta: var2 ztop: var3 zsurface: var4" formula_terms =
"a: var1 b: var2 orog: var3"

There is no dimensionless hybrid height coordinate. The hybrid height is best
approximated as a(k) if a level-dependent constant is needed.

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