Geospace I: Ionospheric Dynamics

ESA's Earth Observation Mission Swarm, launched on 22 November 2013, provides the opportunity of reliable electric current estimates in the ionosphere based on multi-satellite magnetic field measurements. The lower pair, Swarm A/C flying side-by-side at a longitudinal separation of 1.4°, is well suited for determining radial currents. The higher satellite, Swarm B flying at 520 km altitude, provides from time to time well-matched observations with the 50 km lower pair, which can be used for zonal current estimates. We apply in both cases Ampere's ring integral for determining the mean current density passing through the encircled area. Most prominent results are obtained at auroral latitudes where intense field-aligned currents (FACs) are known to flow. Besides the well-know distribution of Region 1 and Region 2 FACs we find significant FACs also inside the polar cap. Interplanetary conditions are identified which favour these currents. Field-aligned and radial currents are also observed at mid and low latitudes, respectively. Here the Swarm results have been used to check theoretical predictions of these current systems. Horizontal currents in the topside F-region are known to be weak. Still, the constellation aspect of the satellite mission has proven to be sensitive enough. We recoved the mean latitudinal distribution and diurnal variation of the tiny zonal current density in the F-region. There are predominantly eastward currents on the dayside and weaker westward currents on the nightside.

Although the primary goal of the Swarm satellite mission is to measure the magnetic signals from the Earth, in order to better understand its planetary magnetic field, the SAFE (Swarm for Earthquake study) project (funded by ESA under the framework “STSE Swarm+Innovation”, 2014) aims at applying the new approach of geosystemics to the analysis of Swarm data for investigating the preparatory phase of earthquakes as seen from space. The main objective is to explore the possible link between magnetic/ionospheric anomalies and large earthquakes analysing Swarm as well as ground based data (seismic, magnetic, GNSS, etc.). This presentation shows the value of this approach for some earthquake case studies . 

The Swarm satellite constellation opens new interesting opportunities in the research of magnetosphere-ionosphere coupling processes. These interactions manifest themselves as bright auroras and rapid variations in the geomagnetic field, which are associated with electric current and conductance variations in the ionosphere. Longitudinal variations in these phenomena are large, particularly in the midnight sector where Swarm with its A+C satellite pair can probe the gradients with a good accuracy. In the presentation we demonstrate how Swarm magnetic field measurements can be used to deduce ionospheric currents in a two-dimensional strip enveloping the satellite trajectories. These maps provide more comprehensive information on auroral currents than similar maps from ground-based magnetometers, because in the latter case only the divergence-free part of the current system (so called equivalent currents) can be resolved. We analyse a set of example events where Swarm has crossed the Fennoscandian MIRACLE network of magnetometers and auroral cameras. Equivalent current patterns from MIRACLE will be compared with the total current patterns from Swarm and their spatial distribution and intensity will be compared with auroral data. We will also discuss the opportunities to estimate ionospheric Hall and Pedersen conductances (or their ratio) with the combination of Swarm and MIRACLE observations.

Large scale currents in the ionosphere are driven by a variety of sources,
including neutral winds, gravity, and plasma pressure gradients. While the
stronger day-time wind-driven currents have been extensively studied,
gravity and diamagnetic currents in the ionosphere have received
little attention, but can have substantial effects even during the night.
With the availability of a new generation of magnetic field models based
on high-accuracy satellite magnetic measurements, it becomes increasingly
important to account for these smaller current systems. In this study,
we use over a decade of high-quality geomagnetic field measurements
from the CHAMP and Swarm missions to study the seasonal, longitudinal,
and local-time structure of the gravity current. These results allow us to
visualize the global structure of this current system and quantify its magnetic
perturbations at satellite altitude.

The Canadian Electric Field Instrument (EFI) onboard the Swarm satellites make continuous high-resolution in situ measurements of the F-region ion drift.   Making 2-D maps of the plasma convection in the high-latitude ionosphere is one way of achieving higher level data products thereby obtaining the maximum benefit from these measurements.   Fiori et al. (2013) and Fiori et al. (2014) have already established that a spherical cap harmonic mapping algorithm can be applied to generate maps of the high-latitude convection pattern based on a Swarm data set that was artificially generated using statistical models to emulate ion drift measurements along hypothetical Swarm satellite tracks.  It was shown that Swarm-based measurements can be successfully mapped both over a localized region surrounding the satellite track (to examine small scale features) and across the entire high-latitude region.  Due to the preliminary nature of the currently available Swarm data we assess the ion drift vectors after removing an offset value which zeros the flow at the convection zone boundary.  This is accomplished through comparison of Swarm ion drift measurements with (1) a statistical convection model and (2) SuperDARN measurements for periods of quasi-stability in the solar wind and interplanetary magnetic field (IMF).