# Geophysical coordinate systems

In geophysics and space physics, individual phenomena or objects can be most conveniently described in different coordinate systems that take into account their specific properties in the most natural and simplest way. For example, the main geomagnetic field is rigidly tied to rotating Earth and, hence, can be best described in geocentric geographic (GEO) or dipole magnetic (MAG) coordinates. There exist several coordinate systems most often used in studies of the geomagnetic field and Sun-Earth connections; their detailed overview can be found in papers by Russell *[Cosmic Electrodyn., v.2, pp. 184-196, 1971]*, Hapgood *[Planet. Space Sci., v.40(5), pp. 711-717, 1992; Ann. Geophys., v.13, pp. 713-716, 1995]*.

## Geopack 2008

**Geopack 2008 is a set of FORTRAN subroutines for transformations between various geophysical coordinate systems and for the main geomagnetic field calculation.**

The package includes 20 subroutines for evaluating field vectors, tracing field lines, transformations between various coordinate systems, and locating the magnetopause position. A new feature, not available in previous releases, is the possibility to take into account the observed direction of the solar wind, which not only aberrates by ~4 degrees from the strictly radial Sun-Earth line, but also often significantly fluctuates around that average direction. Downdload full documentation file (Word, 180 KB).

The most recent revised and extended version *(update of Jan.1, 2020)* of the package GEOPACK-2008 is now available. IGRF-13 model coefficients are currently in use, *extending the time span of the main field model through 2025*.

ATTENTION: see ERRATA for recent corrections/updates (last correction of Geopack-2008 made on November 30, 2010)

Two examples of a typical FORTRAN program, using the GEOPACK-2008 routines for the field line tracing.