# Altitude Adjusted Corrected Geogmagnetic Coordinates

Altitude adjusted corrected geomagnetic (AACGM) coordinates are an extension of corrected geomagnetic (CGM) coordinates that more accurately represent the actual magnetic field. In AACGM coordinates points along a given magnetic field line are given the same coordinates and thus are a better reflection of magnetic conjugacy.

The coordinate system was originally defined by *Baker and Wing* [1989]
in order to compare conjugacy of data from SuperDARN radars located in
Goose Bay, Labrador and Halley Bay, Antarctica. Subsequent updates to the
technique focused on the equatorial region and the south Atlantic anomaly
*Bhavnani and Hein*, 1994; *Hein and Bhavnani*, 1996; *Heres
and Bonito*, 2007].

The software available here uses a new set of AACGM coefficients that more
accurately represent AACGM coordinates. The software and coefficients are
referred to as AACGM-v2 in order to distinguish the results from other
software and coefficients. It is provided without warranty. Details of the
techniques used to derived the new coefficients are described by
*Shepherd*, 2014.

In addition to the software, an online calculator is available for conversions between geographic and AACGM-v2 coordinates: AACGM-v2 calculator

### AACGM Coefficients

Download |
Release |
Description |

aacgm_coeffs-12.tar | 20150207 | Coefficient files for the years 1900-2020 based on the IGRF-12 model. |

IDL v2.4 | 20170601 | tar file that contains IDL software, a test program
and a README file. You must set two
environment variables to run this software. v2.4: inverse MLT
and dipole tilt functions and minor bug fixes, see
release notes for details. |

C v2.4 | 20170601 | tar file that contains C software, a test program
and a README file. You must set two
environment variables to run this software. v2.4: inverse MLT
and dipole tilt functions and minor bug fixes, see
release notes for details. |

### General Notes

The latest coefficients (2020) are derived using the secular variation of
the IGRF-12 model. Small changes in the IGRF-12 2010 coefficients (now DGRF)
result in small changes to AACGM-v2 coordinates beginning in 2005.

Please send questions, comments and bugs to simon *dot* shepherd
*at* dartmouth *dot* edu.

### References

Baker, K. B. and S. Wing (1989), A new magnetic coordinate system for
conjugate studies at high latitudes, *J. Geophys. Res., 94*(a7),
p. 9139, doi:10.1029/JA094iA07p09139.

Bhavnani, K. H. and C. A. Hein (1994), An improved algorithm for computing altitude dependent corrected geomagnetic coordinates, Phillips Lab., Geophys. Dir., Hanscom Air Force Base, Mass., PL-TR-94-2310.

Hein, C. A. and K. H. Bhavnani (1996), An expanded altitude algorithm for computing altitude-dependent corrected geomagnetic coordinates, Phillips Lab., Geophys. Dir., Hanscom Air Force Base, Mass., PL-TR-96-2274.

Heres, W. and N. A. Bonito (2007), An alternative method of computing altitude adjustment [sic] corrected geomagnetic coordinates as applied to IGRF Epoch 2005, Air Force Research Lab., Space Vehicles Dir., Hanscom Air Force Base, Mass., HA-TR-2007-1190.

Shepherd, S. G. (2014), Altitude-adjusted corrected geomagnetic coordinates:
Definition and functional approximations, *J. Geophys. Res. Space
Physics*, *119*, 1–21, doi:10.1002/2014JA020264.
preprint (note that figure numbers
may not have been processed correctly.)