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

General Notes

The latest AACCM-v2 coefficients (2025) are derived using the secular variation of the IGRF-13 model. Small changes in the IGRF-13 2015 coefficients (now DGRF) result in small changes to AACGM-v2 coordinates beginning in 2010.

Coefficients are derived for 5-year epochs from 1590-1895 using the magnetic field model described by Jackson et al., [2000].

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.

Finlay, C. C., S. Maus, C. D. Beggan, T. N. Bondar, A. Chambodut, T. A. Chernova, A. Chulliat, V. P. Golovkov, B. Hamilton, M. Hamoudi, R. Holme, G. Hulot, W. Kuang, B. Langlais, V. Lesur, F. J. Lowes, H. Luehr, S. Macmillan, M. Mandea, S. McLean, C. Manoj, M. Menvielle, I. Michaelis, N. Olsen, J. Rauberg, M. Rother, T. J. Sabaka, A. Tangborn, L. Toffner-Clausen, E. Thebault, A. W. P. Thomson, I. Wardinski, Z. Wei, T. I. Zvereva, and I. A. G. A. Wo (2010), International geomagnetic reference field: the eleventh generation, Geophys. J. Int., 183 (3), 1216, doi:10.1111/j.1365-246X.2010.04804.x.

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.

Jackson, A., A. R. T. Jonkers and M. R. Walker (2000), Four centuries of geomagnetic secular variation from historical records, Phil. Trans. R. Soc. Lond., 358, 957-990, doi:10.1098/rsta.2000.0569.

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.)

Thebault, E., C. C. Finlay, C. D. Beggan, P. Alken, J. Aubert, O. Barrois, F. Bertrand, T. Bondar, A. Boness, L. Brocco, E. Canet, A. Chambodut, A. Chulliat, P. Coisson, F. Civet, A. Du, A. Fournier, I. Fratter, N. Gillet, B. Hamilton, M. Hamoudi, G. Hulot, T. Jager, M. Korte, W. Kuang, X. Lalanne, B. Langlais, J.-M. Leger, V. Lesur, F. J. Lowes et al. (2015), International Geomagnetic Reference Field: the 12th generation, Earth, Planets and Space, 67:79.