Exploring Earth's space environment with the GRACE-FO mission

As part of its attitude and orbit control system, the GRACE-FO satellites carry vector magnetometers. After appropriate calibration and characterisation of artificial magnetic disturbances, the mean residual to the high precision magnetic models is below 1 nT during times of geomagnetic quiet conditions. Furthermore, navigational GPS observations are used to derived data of the total electron content integrated over the upper ionosphere and KBR data are used to derive in situ electron density. These observations are valuable assets to characterize the natural variability of Earth's magnetic field and its space environment. The performance of GRACE-FO magnetic and plasma data is discussed on selected scientific examples. E.g., during magnetic storm events, GRACE-FO, in a constellation with other satellites, reveals the local time dependence of the magnetospheric ring current signature, and monitors significant plasma density enhancements at low and high latitudes. It is further demonstrated that the dual-satellite constellation of GRACE-FO is most suitable to derive the persistence of auroral field-aligned currents with scale lengths of 180 km or longer.

The data derived from non-dedicated observations extends the scientific application areas of the GRACE-FO to space weather and monitoring. Together with similar data sets such as from CHAMP, GRACE, GOCE, and Swarm among others, magnetic and ionospheric monitoring over nearly two solar cycles is available at LEO for different local times or altitudes.