Modeling Earth's Magnetosphere Using Spacecraft Magnetometer Data

The Earth's magnetosphere is a very dynamical system. Its configuration depends on internal and external factors. The first factor is the orientation of the Earth's magnetic axis with respect to the Sun-Earth line, which varies with time because of both the Earth's diurnal rotation and its yearly orbital motion around the Sun. The animation below shows how the magnetospheric field varies in response to the dipole wobbling. 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 only. 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, owing to the high electrical conductivity of the solar wind plasma. Interaction between the terrestrial and interplanetary fields becomes especially effective, when the interplanetary magnetic field is directed antiparallel to the Earth's field on the dayside boundary of the magnetosphere. In this case the 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 following animation:

In actuality, this kind of stationary convection is rarely realized. The solar wind is not steady: periods of quiet flow are often interrupted by strong "gusts", and the interplanetary magnetic field fluctuates both in magnitude and orientation. This results in dramatic dynamical changes of the entire magnetospheric configuration, which culminate in magnetospheric storms, accompanied by an explosive conversion of huge amounts of the solar wind energy into the kinetic energy of charged particles in the near-Earth space, manifested in polar auroral phenomena and ionospheric disturbances. The animation below illustrates the dynamical changes of the global magnetic field in the course of a disturbance: a temporary compression of the magnetosphere by enhanced flow of the solar wind is followed by a tailward stretching of the field lines. Eventually, the increase of the tail magnetic field results in a sudden collapse of the nightside field (a substorm ) and a gradual recovery of the magnetosphere to its pre-storm configuration.


If you have more questions regarding the Earth's magnetosphere and geomagnetism, or would like to refresh your memory of even more general topics, covering basic astronomy and space physics, here is an excellent educational web source, developed by David Stern.


Why do we need the Earth's magnetic field models ?

Modeling of the global geomagnetic field has a unique place in the Sun-Earth connection studies, since that field underlies all processes in the near-Earth space environment: Magnetic fields determine key properties of the geospace plasma, in particular, its anisotropy, which makes it possible to compare observations made in different regions of space by mapping them along the magnetic field lines.

For this reason, understanding the properties of the geospace plasma requires knowing the structure of the geomagnetic field and its dynamics and relation to the state of the solar wind.

The data-based approach is to

Data-based models serve as a bridge between theory and observations, and are the main guide to magnetospheric patterns; deservedly, their role has been compared to that of maps in the exploration of a new country.

What models can do...

Help experimenters Help theorists

What models don't do...


Further information...

Click here for a list of references on the magnetospheric modeling.

Click here to download a GEOPACK source-code library of FORTRAN subroutines. A fully revised version (April 22, 2003) now available. Includes 19 subroutines for evaluating field vectors, tracing field lines, transformations between various coordinate systems, and locating the magnetopause position. Full documentation file: (Word, 100 KB)

Here are two examples of a simple main FORTRAN program, using the GEOPACK routines for the field line tracing

Also available from our anonymous ftp-site .

Click here for downloading a source code (Fortran-77) of the latest version (T01_01, Aug.8, 2001) of the inner and near magnetosphere magnetic field model . Also available from our anonymous ftp-site . See ERRATA for a list of recent corrections/updates (last correction of T01_01: May 14, 2002).

Click here for downloading a source code (Fortran-77) of the T96 model and a documentation file. Also available from our anonymous ftp-site .

Click here if you need a source code of the 1989 version of the model (T89c). Also available from our anonymous ftp-site .

Click here to view the list of data sets used to derive the models.

Click on highlighted items below for latest developments

Modeling the field of a substorm current wedge.

Magnetotail twisting/warping from GEOTAIL/ISEE data.

Using the divergence-free deformation method in the magnetospheric modeling

Polar Cusp: POLAR MFE data and quantitative modeling

Solar Wind Control of the Tail Lobe Field as Deduced From
Geotail, AMPTE/IRM and ISEE-2 Data

Modeling of the Inner Magnetosphere:
The Asymmetric Ring Current and Region 2 Birkeland Currents Revisited

A new data-based model of the near magnetospheric magnetic field with a dawn-dusk asymmetry:
1. Mathematical structure. JGR-A, v. 107 (A8), 2002, (PDF 0.9 MB)
2. Parameterization and fitting to observations. JGR-A, v. 107 (A8), 2002, (PDF 4.1 MB)

Tail plasma sheet models derived from Geotail particle data.
JGR-A, v.108 (A3), 2003. (PDF 1.6MB)

Modeling of the inner magnetosphere during large storms
JGR-A, v.108 (A5), 2003. (PDF 1.6MB)

Global shape of the magnetotail current sheet as derived from Geotail and Polar data
(JGR-A, v.109(A3), 2004) (PDF 1.2MB)



Author and curator:

Dr. Nikolai Tsyganenko, USRA/NASA/GSFC: Nikolai.Tsyganenko@gsfc.nasa.gov

Mail Code 695, NASA/Goddard Space Flight Center, Greenbelt, MD 20771

Phone: (301)-286-7925

Fax: (301)-286-1683


Last updated: Nov. 22, 2004, NAT


NASA Official: R.E. McGuire, Head, Space Physics Data Facility (Code 632, NASA/GSFC), Robert.E.McGuire@gsfc.nasa.gov, (301)286-7794