Modeling the Earth's Magnetosphere Using Spacecraft Magnetometer Data

Space weather is a modern field of space research, focused on the solar activity and its impact upon the near-Earth environment, spacecraft hardware, and humans. It includes investigation and prediction of solar flares, coronal mass ejections (CME), sunspots, magnetic storms, particle precipitation into the Earth atmosphere, and associated ionospheric phenomena. The flow of plasma from the Sun, known as the solar wind, is the principal factor determining the space weather in our planetary system. This is why it is very important to know in advance its principal characteristics: particle density, bulk velocity, the strength and direction of the Interplanetary Magnetic Field (IMF). The NASA Advanced Composition Explorer (ACE) satellite (operating since 1997) and the recently (2015) launched Deep Space Climate Ovservatory (DSCOVR) mission reside at the L1 libration point (1,500,000 km sunward from Earth) and provide continuous flow of information about the solar wind state nearly one hour in advance. Their real-time data are provided online by the National Oceanic and Atmospheric Administration (NOAA) Space Weather Prediction Center (SWPC).

The orientation of the IMF vector is a crucial factor that determines the state of the near-Earth space environment. Southward IMF (Bz<0 in GSM coordinates) combined with a high-speed solar wind result in magnetic storms, which may damage the spacecraft equipment, affect the navigation systems, aircraft and satellite operation. It also results in the so-called "geomagnetically induced electric currents" (GIC) in the ground infrastructures, such as pipelines and electric power grids. For example, on September 1-2, 1859, one of the largest recorded geomagnetic storms caused the failure of the telegraph systems all over Europe and North America. The intensity of geomagnetic storms is quantified by the Dst index, derived from the disturbance of the horizontal H-component of the magnetic field at low and middle latitudes. A rapid decrease of the Dst to low negative values (Dst<-50 nT) manifests the development of a storm. Anyone interested in the current state of space weather can check it at the real-time Dst trend on the webpage of the World Data Center for Geomagnetism (Kyoto).

Here is a very interesting and helpful resource SpaceWeather.com for everyone with even a modest background in space physics. The site provides real-time space weather conditions such as the solar wind parameters, sunspot numbers, solar flares, solar images from SDO (Solar Dynamics Observatory) instruments and NOAA 24 and 48 hour forecasts of the flare and geomagnetic storm probabilities. Besides the space environment data, the website offers up-to-date news on spacecraft scientific missions, breathtaking pictures of auroral displays, stunning atmospheric optical phenomena, noctilucent clouds, and much more interesting information.

Online resources for the geomagnetic field modeling

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].

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.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.

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

Corrected Geomagnetic Coordinates

Invariant Coordinates

A source code for calculating invariant geomagnetic coordinates (L-parameter, invariant latitude) of a location from its geocentric (GEO) coordinates (latitude, longitude, geocentric distance).

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 .

Magnetospheric magnetic field models

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 the fundamental questions:

"What is the actual structure of the geospace magnetic field according to satellite observations?"

"How it is related to changing interplanetary conditions and the ground disturbance level?"