RE: ageostrophic component from operational (u,v) wind fields

• To: IDV Users <idvusers@xxxxxxxxxxxxxxxx>
• Subject: RE: ageostrophic component from operational (u,v) wind fields
• From: Don Murray <dmurray@xxxxxxxxxxxxxxxx>
• Date: Fri, 08 Dec 2006 12:36:07 -0700

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
*************************************************************

• References:
  • ageostrophic component from operational (u,v) fwind ields
    • From: HansPeter Roesli
  • RE: ageostrophic component from operational (u,v) fwind ields
    • From: Fingerhut, William A @ LSC