LOAD_CGM
Name
LOAD_CGM
Purpose
This procedure loads the Correctd Geomagnetic Grid (CGM) for all
latitude and longitudes for a given year. The grid can be binned
on geomagnetic or geographic. Also returned are LSHELL and Bz.
Category
SNOE, mapping, coordinates, magnetic
Calling Sequence
LOAD_CGM, Data
Inputs
None
Optional Inputs
None
Keyword Parameters
YEAR: Set this to the year of the CGM model to use
[ VALID: 1998 through 2002 ]
[ DEFAULT: 1999 ]
GRID: Set this to the grid that the data should be binned on
[ VALID: 'geo' or 'mag' ]
[ DEFAULT: 'geo' ]
B_ONLY: Set this keyword to only return the magnetic field strength
SNOE_COORDS: Set this keyword to return the data on the SNOE
coordinate system (-180 to 180 longitude, rather than 0 to 360)
Outputs
Data: This procedure returns an array of geographic latitude,
longitude, geomagnetic latitude, longitude, Bz (magnetic field
strength), and Lshell, gridded on the requested coordinate
systems.
The data array returned is a FLTARR( 361, 181, 6 ).
The 3rd dimension is [ gLat, gLon, mLat, mLon, Lshell, Bz ]
Each of these is FLTARR( 361 lon, 181 ), or (Lat,Lon).
The longitudes run from 0 to 360 or -180 to 180 if /SNOE_COORDS set
**The latitudes run from -90 to 90. Up-side down.**
Lat having 360 and Lon having 180 is counter-intuitive, but
think of it this way: The latitude ring on the globe at the
equator has 360 possible longitude values. A longitude column
on a globe has only 180 possible values. See the EXAMPLES
section, maybe it will help.
Restrictions
Requires the CGM datasets (in !snoe.p.base+'other/CGM/')
Procedure
* See code.
* http://nssdc.gsfc.nasa.gov/space/cgm/cgm.html
* http://nssdc.gsfc.nasa.gov/space/model/models/igrf.html
This websites have interactive ways to test and verify the data.
Example
LOAD_CGM, data
LOAD_CGM, data, year=1999, grid='mag', /SNOE
To print the geographic coordinates of the geomagnetic north pole:
LOAD_CGM, data, grid='mag'
print, data[ 180, 90+90, 0:3 ] ;;; = [glat,glon,mlat,mlon] @ [90,0] magn
To print the geographic coordinates of the geomagnetic south pole:
LOAD_CGM, data, grid='mag'
print, data[ 180, 90-90, 0:1 ] ;;; = [glat,glon,mlat,mlon] @ [-90,0] magn
To print the magnetic coordinates of Boulder (40N, 105W):
LOAD_CGM, data, grid='geo'
print, data[ 105, 90+40, [2,3] ]
Modification History
Written by: Ted Fisher, 2000.
2002-07-23; KDM; Added documentation
2002-07-25; KDM; Switched path to !SNOE.p.base
2002-09-18; KDM; Switched to /SWAP_IF_LITTLE_ENDIAN so its portable