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; 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].

This website offers a set of FORTRAN subroutines for transformations between various
geophysical coordinate systems.
The most recent revised and extended version (**update of Jan.31, 2015**)
of the package **GEOPACK-2008** is now available.
IGRF-12 model coefficients are currently in use, extending the time span of the main field model through 2020.

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, Tsyganenko and Sitnov, 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?"__

Follow the links below to download FORTRAN source codes of data-based models, developed by the author of this web resource during the last 25 years.

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

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)**

(An invited review, published in Annales Geophysicae, October 21, 2013) (Full article, PDF ~10MB).

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)**

(Published in Annales Geophysicae, January 6, 2015) (PDF ~11MB).

A new forecasting model (TA15) of the magnetosphere, driven by optimal solar-wind coupling functions **(abstract)**

("Early view" version of JGRA paper, Oct.10, 2015)

(A concise description of the model, pdf~1.5MB)

(Fortran source codes and yearly input parameter files for 1995-2015)

**Dr. Nikolai Tsyganenko**
**Ms. Varvara Andreeva**

**nikolai.tsyganenko@gmail.com**
**varandreeva@gmail.com**

**n.tsyganenko@spbu.ru**

Department of Earth's Physics, University of St.-Petersburg, Petrodvoretz, St.-Petersburg 198504, Russian Federation

Phone: +7-812-428-4634

Fax: +7-812-428-7240

** Most recent update:
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October 12, 2015 (a new TA15 model link added with source codes and input data)
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** Previous updates:
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**
March 23, 2015 (update of TS05 model parameters for 2014, due to NSSDC revision of 2014 OMNI data)**

**
Jan 31, 2015 (IGRF-12 coefficients included in Geopack-2008)**

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Nov 12, 2014 (a refurbished version of T89 source code added)
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Nov 04, 2014 (TS05 model parameters through Sep 30, 2014, updated/added)
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Nov 21, 2013 (TS05 model parameters through Sep 28, 2013, updated/added)
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March 11, 2011 (a SAVE statement was added in the source code of the T96 model,
to avoid run-time problems with some Fortran compilers).
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**
Dec 8, 2010 (TS05 model parameters for Jan 1 - Nov 7, 2010 added);
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December 1, 2010 (Earth's main field model extended by adding IGRF-11 coefficients
in the Geopack-2008 s/w;
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**
March 13, 2010 (licensing info added);
February 25, 2010; June 11, 2009; March 3, 2009; April 21 and July 31, 2008.
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