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APEX (2025-05)

Apex geomagnetic coordinate system

Model Description

Fortran code to convert between geographic and magnetic quasi-dipole, magnetic apex, and modified magnetic apex coordinate systems based on Van Zandt et al. (1972) and Richmond [1995]. The geomagnetic main field is the International Geomagnetic Reference Field (IGRF) Version 13. The test program includes:

Magnetic apex parameters for a given location
Base vectors for scaling electric field and ion velocity components
Magnetic footpoints in both hemispheres for a given geographic point
Conversion between quasi-dipole and geographic coordinates
Subsolar point, solar zenith angle, magnetic local time

Model Figure(s) :

Model Inputs Description

Date and time, positions (geographic longitude, latitude, altitude)

Model Outputs Description

Magnetic apex parameters for a given location
Base vectors for scaling electric field and ion velocity components
Magnetic footpoints in both hemispheres for a given geographic point
Conversion between quasi-dipole and geographic coordinates
Subsolar point, solar zenith angle, magnetic local time

Model Caveats

Change Log

05/2025:

Update to add the ability to read the IGRF coffecients from the file provided by NGDC at https://www.ngdc.noaa.gov/IAGA/vmod/coeffs/igrf14coeffs.txt.  This will be come the default behavior with the next update of IGRF.
  
Includes IGRF-14 coefficients published in late 2024

Model Acknowledgement/Publication Policy (if any)

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Curator: Chiu Wiegand | NASA Official: Dr. Masha Kuznetsova | Privacy and Security Notices | Accessibility | CCMC Data Collection Consent Agreement