A method to derive maps of ionospheric conductances, currents, and convection from the Swarm multisatellite mission

Abstract

The European Space Agency (ESA) Swarm spacecraft mission is the first multisatellite ionospheric mission with two low-orbiting spacecraft that are flying in parallel at a distance of~100-140 km, thus allowing derivation of spatial gradients of ionospheric parameters not only along the orbits but also in the direction perpendicular to them. A third satellite with a higher orbit regularly crosses the paths of the lower spacecraft. Using the Swarm magnetic and electric field instruments, we present a novel technique that allows derivation of two-dimensional (2-D) maps of ionospheric conductances, currents, and electric field in the area between the trajectories of the two lower spacecraft, and even to some extent outside of it. This technique is based on Spherical Elementary Current Systems. We present test cases of modeled situations from which we calculate virtual Swarm data and show that the technique is able to reconstruct the model electric field, horizontal currents, and conductances with a very good accuracy. Larger errors arise for the reconstruction of the 2-D field-aligned currents (FAC), especially in the area outside of the spacecraft orbits. However, even in this case the general pattern of FAC is recovered, and the magnitudes are valid in an integrated sense. Finally, using an MHD model run, we show how our technique allows estimation of the ionosphere-magnetosphere coupling parameter K, if conjugate observations of the magnetospheric magnetic and electric field are available. In the case of a magnetospheric multisatellite mission (e.g., the ESA Cluster mission) several K estimates at nearby points can be generated.

Field‐Aligned and Horizontal Currents in the Northern and Southern Hemispheres From the Swarm Satellite

“…Each auroral oval crossing by the parallel-flying A and C satellites are analyzed by utilizing the SECS method (Amm et al, 2015). Each auroral oval crossing by the parallel-flying A and C satellites are analyzed by utilizing the SECS method (Amm et al, 2015).…”

“…The CF SECS represents a current system which is CF and poloidal and causes a toroidal magnetic field. The Swarm/SECS method was tested with synthetic models by Amm et al (2015) and with measurements by Juusola et al (2016). The Swarm/SECS method was tested with synthetic models by Amm et al (2015) and with measurements by Juusola et al (2016).…”

“…Using the estimated values of the scale factors I in the definition of the SECS basis functions (Amm et al, 2015), the ionospheric horizontal current J is calculated as a sum of the individual elementary systems. In the following discussions we will equate the FAC j || with the radial current, which is estimated from the divergence of the horizontal current as || = ±∇ · J.…”

“…In data analysis, we will utilize the spherical elementary current systems (SECS) data analysis method (Amm et al, 2015;Juusola et al, 2016). In data analysis, we will utilize the spherical elementary current systems (SECS) data analysis method (Amm et al, 2015;Juusola et al, 2016).…”

Use of spherical elementary currents to map the polar current systems associated with the geomagnetic sudden commencements on 2013 and 2015 St. Patrick's Day storms

“…Later on [ Weygand et al ., ], these equivalent currents were compared with ionospheric flow vectors measured by the Super Dual Auroral Radar Network radars, demonstrating that SECS can help us understand the magnetosphere‐ionosphere coupling mechanisms using ground arrays combined with magnetospheric spacecraft data and that they can be used as input for other techniques. Accordingly, it served to combine field‐aligned currents (FACs) from the Cluster II fleet of satellites with two‐dimensional ground magnetic data so as to calculate actual (not equivalent) ionospheric currents [ Amm , ] or, recently, to derive maps of ionospheric conductances, currents, and electric field in the area between the trajectories of the two Swarm lower spacecraft [ Amm et al ., ]. After the work of Pulkkinen et al .…”