From: Tom Roche <Tom_Roche_at_nyahnyahspammersnyahnyah>

Date: Tue Jan 08 2013 - 12:12:37 MST

Date: Tue Jan 08 2013 - 12:12:37 MST

summary: is the "height"

* returned by stdatmus_p2tdz

* input to stdatmus_z2tdp

geometric? and is it above ground level (AGL), above mean sea level

(AMSL) or other? (Apologies for any lack of meteorological literacy.)

details:

I'm working toward a 3D-regrid of source data that is horizontally

global and spherical (lon-lat) and vertically hybrid sigma-pressure

(hσp) toward a target that must be regional (over CONUS) and Cartesian

(LCC). (I must merge a netCDF data variable--N2O concentration--into a

target file containing concentrations of many other species, but not

N2O.) Unfortunately ESMF_regrid(...) cannot do this directly; I must

first convert my source/input to a Cartesian grid.

I can convert hσp -> pressure using NCL::pres_hybrid_ccm

http://www.ncl.ucar.edu/Document/Functions/Built-in/pres_hybrid_ccm.shtml

and pressure -> "height" using NCL::stdatmus_p2tdz

http://www.ncl.ucar.edu/Document/Functions/Built-in/stdatmus_p2tdz.shtml

*> If p is a scalar, then a one-dimensional array of length 3 will be
*

*> returned. Element (0) will contain the temperature [C]; (1) will
*

*> contain the density [kg/m^3] and (2) will contain height [m].
*

But I'm wondering,

* is this height geometric? (which presumably I need for a Cartesian

transform). I'm guessing it is, from the units, but would like to be

sure.

* if geometric, what is the reference datum for that height? I'm hoping

it's MSL, but need to be sure.

Presuming the height is AMSL, then presumably by

1. cropping the source grid to the horizontal bounds of my target grid

2. converting the source hσp to geometric height AMSL (gh_AMSL) via

(pcode) (stdatmus_p2tdz(pres_hybrid_ccm(hσp)))[2]

I could convert my global source to a Cartesian form suitable for

ESMF_regrid'ing into horizontal over CONUS LCC with vertical gh_AMSL.

Call that "the intermediate grid."

I can also determine the target layers' gh_AMSL more directly: in

addition to specifying the hσp of layer middles and tops, the target

also specifies the mean (surface) terrain elevation (AMSL) for each

gridcell, and the height AGL for the middle and top of each (gridcell,

layer) tuple. Presuming the intermediate and target gh_AMSL match (to

some reasonable precision) I could then in good conscience merge the

concentrations from the intermediate grid into the target grid.

Am I missing something?

TIA, Tom Roche <Tom_Roche@pobox.com>

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Received on Tue Jan 8 12:12:57 2013

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