Ionospheric scale lengths derived from the Swarm and GRACE-FO constellation missions

Abstract:

In situ measurements onboard Low Earth-Orbiting (LEO) satellites have significantly contributed to exploring the global ionosphere/thermosphere. Simultaneous observations from multiple platforms in constellation provide specific knowledge on scale lengths of the investigated phenomenon. This presentation reviews some aspects of these topics that have been achieved from data of the operational Swarm and GRACE-FO missions. The Swarm constellation of three identical spacecraft was flown in a nearly string of pearls configuration for its first 2 months and consists now of a pair flying side-by-side with a 1.4° longitudinal separation at the equator and the third satellite at a different local time. The two satellites of the GRACE-FO mission have same orbits, but with one satellite following the other with a separation of about 220 km. We have used newly calibrated magnetic data from the latter and investigated the correlation lengths of polar field-aligned currents (FACs) of different scales and compare them with earlier studies based on the Swarm constellation.

Electron density data from the Swarm constellation were also applied to investigate equatorial plasma depletions. For zonal separations between the Swarm satellites larger than 0.4° during the first months of the mission, no significant correlation was found throughout local night, suggesting that plasma density scale sizes less than 44 km in the zonal direction are significant. However, in early evening hours (around 1900 LT), we could occasionally find good correlations between structures in the data of the two satellites, also for zonal separations of 1.4° when the final constellation was reached. We interprete such structures as initial perturbations of the post-sunset plasma depletions.

In the future, a particular opportunity may be provided by ESA’s candidate mission Daedalus where the benefit of dual-satellite operations is currently investigated.