Hi-
This message went to the list owner instead of the list, but
is relevant. It's a quite ingenious method for accomplishing
the task. Thanks, Bill!
However, this only works for grids in a non-lat/lon
projection like the CONUS grids. As Dave S. noted, the IDV doesn't
handle the derivative of lat/lon correctly (since distance between
lon lines varies).
We hope to add some new formulas for things like geostrophic
and ageostrophic winds (and fix the lat/lon problem) in the
coming months. It didn't make it into the 2.1 release unfortunately.
So many things, so little time. ;-)
Don Murray
------- Forwarded Message
To: "HansPeter Roesli" <satmet.hp@xxxxxxxxxx>
cc: <owner-idvusers@xxxxxxxxxxxxxxxx>
From: "Fingerhut, William A @ LSC" <William.Fingerhut@xxxxxxxxxxx>
Subject: RE: ageostrophic component from operational (u,v) fwind ields
Organization: UCAR/Unidata
Keywords: 200612081544.kB8FiEXX013963
I have a cludgy jython method that computes geostrophic wind,
which one could easily modify or 'use' to compute the ageostrophic wind.
To use it, I first select a dataset (model data);
then use a formula: geoWind(height_grid)
which uses the jython method:
#
# geostrophic wind
#
def geoWind(h):
from ucar.unidata.data.grid.DerivedGridFactory import *
z=3D0.*h
o=3Dz-1
vg=3D100.*DerivedGridFactory.createHorizontalAdvection(h,o,z)
ug=3D-100.*DerivedGridFactory.createHorizontalAdvection(h,z,o)
return DerivedGridFactory.createTrueWindVectors(ug,vg)
The constant 100 includes the correct constant for the geostrophic wind,
a constant latitude, and a scaling factor. The constants, 0 and 1,
allow me to use the existing code to calculate each partial derivative
of height.
If anyone has another method, I would like to hear about it.
Bill
< Bill Fingerhut, Professor PHONE: 802-626-6257 >
< Meteorology Dept FAX: 802-626-9770 >
< Lyndon State College >
< Lyndonville, Vt 05851 >
< >
< EMAIL: william.fingerhut@xxxxxxxxxxxxxxx >
< bfingerhut@xxxxxxxxxxxxxxxx >
< WWW: http://apollo.lsc.vsc.edu/ <http://apollo.lsc.vsc.edu/>
< >
< disclaimer: I know nothing - I only work here. >
*************************************************************
Don Murray UCAR Unidata Program
dmurray@xxxxxxxxxxxxxxxx P.O. Box 3000
(303) 497-8628 Boulder, CO 80307
http://www.unidata.ucar.edu/staff/donm
*************************************************************
