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			 **   THE GEM MESSENGER   **
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						     Volume 6, Number 8 
						     March 14, 1996

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ANNOUNCEMENT OF ALTITUDE ADJUSTED CORRECTED GEOMAGNETIC COORDINATES
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From: Kile Baker (JHU/APL) and Fred Rich (Phillips Laboratory)

WWW reference:  http://sd-www.jhuapl.edu/RADAR/AACGM.html

Many members of the space science community have been using the PACE
(Polar Anglo-American Conjugate Experiment) magnetic coordinate system
(hereafter referred to as the PGM system).  This was a coordinate 
system based on Corrected Geomagnetic Coordinates (CGM), another 
popular magnetic coordinate system for space science use.  The PGM 
system was defined to be the same as CGM at 0 km altitude.  At other
altitudes the PGM system was defined so that the latitude and 
longitude were invariant along a magnetic field line.

A new version of this coordinate system has been prepared for the 
Space Forecasting Center.  Because the system has found application
beyond the PACE program, this updated version has been renamed the 
Altitude Adjusted Corrected Geomagnetic Coordinate System (AACGM).

The new software has a much higher accuracy than the original PGM 
system and also runs much faster.  The new version provides coordinate
systems based on the IGRF 1990 and 1995 magnetic field models.  The
original PGM system was derived from IGRF 1985 plus secular terms to
give a 1988 field model.

The basic FORTRAN routines to convert from geographic to AACGM (and
vice versa) for the 1995 model, can be obtained from Phillips
Laboratory via anonymous ftp.  Connect to ph4000.plh.af.mil;  change
directory to AACGM and get the file SFCNEW95.FOR.

Alternatively, if you want both the 1990 and 1995 coordinates as well as 
routines for calculating magnetic local time and interface routines to 
allow the software to be used from IDL, you can get the software from
The Johns Hopkins University Applied Physics Laboratory.  If you have
a World-Wide-Web browser, such as Netscape, you can find out more 
about the coordinate system by connecting to the URL 
           http://sd-www.jhuapl.edu/RADAR/AACGM.html.  
You can also download the software via the web.  If you want to 
download the software via ftp, connect to SuperDARN-ftp.jhuapl.edu;
change directory to darn/hp/pgm.  If you can read a tar archive, you
can simply get the file AACGM.tar.  Alternatively you can get each 
of the individual files in the darn/hp/pgm directory.  The software
at this site includes a UNIX makefile which can be easily modified 
for different systems.

If you decide to download this software we would request that you 
send a mail message to Kile_Baker at jhuapl.edu and rich at plh.af.mil to
let us know that the system is being used.  It will also help us 
provide you with support for any bug fixes or improvements.

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