With the advent of space era and understanding the crucial role of the geomagnetic field in the dynamics of the Earth's upper atmosphere and radiation belts, a need was realized to extend the models from low to high altitudes, eventually including the entire magnetosphere, an integral part of our space environment. Modeling the magnetic field in that region is much more difficult, mostly because the magnetic field from external sources (currents in the magnetospheric plasma) rapidly outweighs the main field with growing distance from Earth. The external field is not current-free and, hence, it is no longer possible to conveniently represent it by a scalar potential, uniquely defined by observations at a surface, as was the case with the main field. Rather, vector measurements of the magnetic field should now be made throughout the entire 3D modeling region, making it necessary to accumulate large amounts of space magnetometer data taken in a wide range of geocentric distances.

This task turns out to be even more complicated due to the fact that, unlike the main
geomagnetic field that varies on a timescale of thousands of years, the Earth's magnetosphere
is a very dynamical system, whose configuration depends on many internal and external factors.
The first factor is ** orientation of the Earth's magnetic axis ** with respect to the direction
of the incoming solar wind flow, which varies with time because of (i) Earth's diurnal rotation and
its yearly orbital motion around Sun, and (ii) frequent "side gusts" of the solar wind. The
** animation on the left below** shows how the magnetospheric field varies in response to the diurnal
wobbling of the geodipole. The background color coding displays the distribution of the
scalar difference DB between the total model magnetic field and that of the Earth's dipole
alone. Yellow and red colors correspond to the negative values of DB (depressed field
inside the ring current, in the dayside polar cusps, and in the plasma sheet
of the magnetotail). Black and blue colors indicate a compressed field
(in the subsolar region on the dayside and in the magnetotail lobes on the
nightside).

Another important factor is the state of the solar wind, in particular, the
orientation and strength of the ** interplanetary magnetic field **,
"carried" to the Earth's orbit from Sun due to the high electrical
conductivity of the solar wind plasma. Interaction between the terrestrial
and interplanetary fields becomes much more effective when the interplanetary
magnetic field turns antiparallel to the Earth's field on the dayside boundary
of the magnetosphere. In this case, geomagnetic and interplanetary field lines
connect across the magnetospheric boundary, which greatly enhances the transfer
of the solar wind mass, energy, and electric field inside the magnetosphere.
As a result, the magnetospheric field and plasma become involved in a **convection**,
as illustrated in the ** second animation below
(right)**:

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; a detailed overview of those systems 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]; there also exist comprehensive online resources, such as
SPENVIS page.

This website offers a set of FORTRAN subroutines for transformations between various
geophysical coordinate systems.
The most recent revised and extended version (**update of Dec.01, 2010**)
of the package **GEOPACK-2008** is now available.
IGRF-11 model coefficients are now added, extending the time span of the main field model through 2015.

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.
Full documentation file: (Word, 180 KB)

Double-precision version: **(GEOPACK-2008_dp)**

**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

**Licensing information**: All programs/codes presented on this site is free software: you can download,
redistribute and/or modify it under the terms of the GNU General
Public License as published by the Free Software Foundation, either version 3 of the License,
or any later version.
A copy of the GNU General Public License can also be found at
GNU website .

The data-based approach to the modeling of the geomagnetosphere has been developed over
the last 3 decades, starting with the pioneering work by Mead and Fairfield [1975].
Subsequent efforts [Tsyganenko and Usmanov, 1982; Tsyganenko, 1987, 1989, 1996, 2002, 2003, 2005] resulted
in more refined models, used since then in many studies. The principal goal of the data-based magnetosphere
modeling is to extract full information from large sets of available data
, bridge the gap between theory and observations, and help answer a fundamental
question __"What is the actual
structure of the geospace magnetic field and how is it related to changing interplanetary
conditions and the ground disturbance level?"__

Links below can be used for downloading FORTRAN source codes of data-based models, developed by the author of this web resource during the last 25 years.

- A source code for the
**TS05 (aka TS04)**, a dynamical empirical model of the inner storm-time magnetosphere. Click**here**for a detailed description of the model. -
Yearly input data files (from 1995 through September 30, 2014) and related documentation for the TS05 model .
- Click here to download a source code (Fortran-77)
of the T02 (aka T01_01) model of the inner and near magnetosphere. Publications:
**Paper I**and**Paper II**. - Click here to download a source code (Fortran-77) of the
**T96 model**. More detailed information on the model:**Paper I**and**Paper II**. - Click here if you need a source code of the 1989 model (T89d_SP) (or here for its double-precision version (T89d_DP).)
- Click here to view the list of
**data sets**used in the derivation of the models. -
Data-based modeling of the geomagnetosphere with an IMF-dependent magnetopause
**(abstract)**

(Published in Journal of Geophysical Research, January 23, 2014) -
On the bowl-shaped deformation of planetary equatorial current sheets
**(abstract)**

(Published in Geophysical Research Letters, February 4, 2014) -
Internally and externally induced deformations of the
magnetospheric equatorial current as inferred from spacecraft data
**(abstract)**

(accepted by Annales Geophysicae, Nov 28, 2014) (Full preprint, PDF ~20MB).- A fortran subroutine for the new equatorial current sheet model (double precision)

**Author and curator:**

**tsyganenko@geo.phys.spbu.ru****n.tsyganenko@spbu.ru**Department of Earth's Physics, Institute of Physics, University of St.-Petersburg, Petrodvoretz, St.-Petersburg 198504, Russian Federation

Phone: +7-812-428-4634Fax: +7-812-428-7240

**This site was started on February 15, 2008****The most recent update:****Dec 18, 2014 (a preprint of the paper on the equatorial current sheet deformation and related source code)****Previous updates:****Nov 12, 2014 (a refurbished version of T89 source code added)****Nov 04, 2014 (TS05 model parameters through Sep 30, 2014, updated/added)****Nov 21, 2013 (TS05 model parameters through Sep 28, 2013, updated/added)****March 11, 2011 (a SAVE statement was added in the source code of the T96 model, to avoid run-time problems with Intel Fortran compilers).****Dec 8, 2010 (TS05 model parameters for Jan 1 - Nov 7, 2010 added);****December 1, 2010 (Earth's main field model extended by adding IGRF-11 coefficients in the Geopack-2008 s/w;****March 13, 2010 (licensing info added); February 25, 2010; June 11, 2009; March 3, 2009; April 21 and July 31, 2008.**

See ERRATA for a list of recent corrections/updates (last correction of T02 and TS05: June 24, 2006).

**Click on highlighted items below for latest developments:**

Magnetospheric configurations from a high-resolution data-based magnetic field model **(abstract)**

(JGR-A, v.112(A6), 2007) (PDF 2.3MB).

Dynamical data-based modeling of the storm-time geomagnetic field with enhanced
spatial resolution **(abstract)**

(Published in JGR-A, July 30, 2008) (PDF ~21.0MB).
**Note:** The two papers cited above present main ideas and first results obtained
using a **new approach to the data-based modeling**. Its essence boils down to
(1) employing extensible high-resolution expansions for the field of equatorial
currents and (2) a special data mining technique based on a "nearest-neighbor"
search in the parameter space. More details on the advanced modeling methods
and results can be found on a webpage, maintained by Mikhail Sitnov
(JHU/APL).

Magnetic field and electric currents in the vicinity of polar cusps
as inferred from Polar and Cluster data **(abstract)**

(Published in Annales Geophysicae, April 2, 2009) (PDF ~3.0MB).

On the reconstruction of magnetospheric plasma pressure distributions
from empirical geomagnetic field models **(abstract)**

(Published in JGR-A, July 15, 2010) (Full article, PDF ~1.2MB).

Data-based modeling of our dynamic magnetosphere **(abstract)**

(Published in Annales Geophysicae, October 21, 2013) (Full article, PDF ~10MB).