At mid- and low-latitudes during quiet geomagnetic times, electrical currents flowing in the ionosphere generate magnetic variations of a few tens of nanoteslas (nT) at the Earth's surface and at low-Earth orbit altitudes. The Sq ("solar quiet") current system forms two large-scale vortices on the dayside, one in each hemisphere. A stronger current, the equatorial electrojet (EEJ), flows along the dip equator and generates magnetic signatures that can reach up to 150 nT at some locations.
The Dedicated Ionospheric Field Inversion (DIFI) model is a time-varying, spherical harmonic representation of the quiet-time Sq and EEJ magnetic fields between +/- 55 degrees quasi-dipole latitudes. It is derived from a combination of Swarm satellite and ground-based magnetic observatory data. Temporal variations are represented using Fourier series with periods of 24, 12, 8 and 6 hours, modulated by annual and semiannual periods. The spherical harmonic expansion extends to degree 60 and order 12 in geomagnetic dipole coordinates. Solar activity (represented by the F10.7 index) dependence is also included in the model. DIFI provides both the primary (external) and induced (internal) magnetic fields components.
DIFI-7 is not the most recent DIFI model; DIFI-8 is a more recent version. DIFI-7 includes 0602/0603 L1b Swarm data and observatory data between Dec 1, 2013 and May 31, 2022.
The DIFI model is developed by CIRES in collaboration with the Institut de Physique du Globe de Paris (IPGP) through the Swarm DISC (Swarm Data, Innovation, and Science Cluster), a project funded by the European Space Agency (ESA). DIFI is an official level 2 product of the Swarm mission. DIFI models and other Swarm level 2 products are also available at http://swarm-diss.eo.esa.int.
| Available DIFI-7 Downloads | ||||
|---|---|---|---|---|
| Type | Format | Mbyte | Contents | |
 | Model Coefficients | ASCII | 2.2 | DIFI-7 spherical harmonic coefficients |
| Article | 3.5 | "First results from the Swarm Dedicated Ionospheric Field Inversion chain" (2016 paper describing an earlier DIFI model) | |
| Article | 2.1 | "Swarm SCARF Dedicated Ionospheric Field Inversion chain” (2013 paper describing the DIFI algorithm and the coefficient file format) | |
| Python Module | Python | ... | Software available upon request. Please email geomag.models@noaa.gov |
| Animation | AVI | .8 | Time evolution of the DIFI current system on January 1 |
| Animation | AVI | .8 | Time evolution of the DIFI current system on April 1 |
| Animation | AVI | .8 | Time evolution of the DIFI current system on July 1 |
| Animation | AVI | .8 | Time evolution of the DIFI current system on October 1 |