Swarm, ESA's four-satellite magnetic field and geospace explorer, is presently in its extended mission. A late 2017 extension review and subsequent approval by Member States mandated the mission to aim for a broadening of the mission and exploitation context in essentially all science domains. The same review also highlighted the fact that Swarm constellation is a unique resource in low Earth orbit, which should be managed and funded with a long-term perspective in mind. Practically, that would imply at least one complete solar cycle.
This presentation details the status of the extended mission implementation versus the augmented objectives, including orbit adjustments and product portfolio increments, and also outlines the Agency's plans for the years ahead. Finally, the presentation aims at presenting the ongoing and planned R&D efforts and opportunities that are offered to the community, including relevant funding aspects.

The Swarm mission inludes the first orbital application of high-resolution (64 pixels diameter with full coverage of the detector plane), 2-D imaging of low-energy ion and electron populations through CCD-based signal detection. This technology has provided ion flow velocities with a resolution of the order of ten m/s and better, derived from ion distributions reduced partially on board in the case of Thermal Ion Imagers on Swarm A-C. On Swarm Echo (ePOP), the Suprathermal Electron/Ion imager collects full images at a rate of 100 per second in time-limited bursts, enabling analysis of higher-order features of the particle distributions, including for example bulk temperature as a function of pitch angle, and field-aligned flows and beams.

This talk will highlight scientific findings made possible by this technology. For example, using Swarm A-C, Archer et al. [2015] identified high-altitude nightside ion flow channels that, though occurring during very low geomagnetic activity, are intense enough to generate highly anisotropic ion temperatures approaching 10,000 K, along with large ion upflows. Archer et al. [JGR, 2017] showed that these channels occur frequently during quiet periods, and are associated with the boundary of the large-scale R1/R2 FAC systems, where Pedersen current is maximum. Another type of intense ion flow channel was identified in the dusk sector in connection with the aurora-like "STEVE" phenomenon [MacDonald et al., Science Adv., 2018].

Also based on Swarm A-C observations, correlated electric and magnetic fluctuations were analyzed by Pakhotin et al. [JGR, 2018], revealing the presence of coherent standing Alfven waves (SAW) and demonstrating the importance of time-varying fields in M-I coupling. Miles et al. [GRL, 2018] used a similar analysis to identify a SAW within a double auroral arc system imaged with the Swarm E Fast Auroral Imager. Wu et al. [this conference] determine the conditions under which such coherent time-varying field regions occur, and their locations relative to large-scale current sheets and auroral arcs. van Irsel et al. [also this conference] demonstrate a technique based on the process of ambipolar diffusion for estimating the ion-neutral collision frequency in the topside ionosphere using measurements of vertical ion drift and electron temperature.

Using the SEI high-time-resolution particle imager on Swarm Echo, Cameron and Knudsen [JGR, 2016] found energy-dispersed field-aligned electron bursts which were determined to be a potential signature of fast-moving auroral rays. Shen et al. [JGR, 2018; also this conference] used the SEI in ion mode to detect intense ion heating regions within auroral return currents at altitudes significantly lower than observed ever before. Shen and Knudsen [submitted to JGR, 2018] used the SEI to identify the first reported occurrences of strong electron heating (to energies of more than 300 eV) perpendicular to the geomagnetic field.

These examples are meant to illustrate some of the many possible applications of high-resolution particle imaging, on Swarm as well as future missions.

Our knowledge of the electrodynamics of Earth's upper-atmospheric plasma environment has been acquired largely through radio and radar sounding from the ground, and in situ measurements from single spacecraft. Measurements from single satellites are fundamentally ambiguous because it is usually not possible to decompose a measurement signal into its time-varying and space-varying parts. In studying the ionosphere, most studies rest upon one or the other assumption, that is, that the signals reported by a magnetometer or electric field instrument are either mainly time-varying (that is, Alfvenic) or mainly spatial structure doppler shifted by the rapidly moving satellite, and sometimes both. ESA’s Swarm is the first multi-satellite mission within the F region ionosphere that has been capable of resolving the space-time measurement ambiguity of the electrodynamic environment. Swarm consists of three approximately identical satellites in low Earth orbit, each carrying instrumentation enabling measurements of Earth’s electrodynamic environment. In this presentation we present a new technique, called Swarm current-and-drift (CAD) scanning, for resolving the temporal variability of ionospheric field-aligned electric current density and ion drifts. The method uses the three Swarm satellites in their pearls-on-a-string configuration from early in the commissioning phase of the mission. We examine phase relationships between the currents and drifts at high latitudes, and assess their temporal and spatial variability, as well as limitations of the technique, including effects of temporal aliasing on the results.

3-D electrical conductivity distribution in the lower mantle (depth range ~ 400- 1600 km) can be estimated by inverting so-called matrix Q-responses. These responses relate spherical harmonic coefficients of external (inducing) and internal (induced) parts of the magnetic potential which describes the signals of magnetospheric origin. Currently, time series of these coefficients are estimated within Comprehensive Inversion framework using potential method. However, the quality of the estimated induced coefficients containing information about 3-D conductivity remains insufficient, thus limiting recovery of lateral conductivity variations in the mantle.
Here, we explore a feasibility of alternative approach for retrieving time series of inducing (and induced) coefficients. We utilize the fact that horizontal component of magnetic field is much less influenced by effects from 3-D inhomogeneities of the Earth when compared to the vertical component. Therefore, we first estimate time series of inducing coefficients by analysing only horizontal component assuming some prior Earth’s background conductivity model. With time series of inducing coefficients at hand, we determine induced coefficients by analysing vertical component only. This study shows application of the alternative approach to the observatory and Swarm data.

The ESA Swarm mission includes three identical spacecrafts, which carry magnetometers for their main objective of investigating the Earth’s magnetic field at unprecedented high accuracy in terms of both temporal and spatial resolution. The constellation also carries accelerometers and GPS receivers, which are used to derive non-gravitational accelerations and thermosphere density data. These result in L2 products used for a secondary mission objective: studying the influence of geomagnetic activity on the thermosphere.
The GPS data results in low frequency accelerations and densities, accurate at 20 minutes to once per orbit time scales, depending on the altitude and activity level, available for Swarm A, B and C. High frequency thermosphere density data, with 10 second sampling, come from a combination of the non-gravitational accelerations derived from the GPS receiver and measurements of the accelerometer, corrected for several instrument effects. The processing of this high frequency data is only feasible for Swarm C.
In this work, the current status of the thermospheric neutral density products is presented, in particular with a comparison between low and high frequency data. Additionally, the study focuses on the thermosphere density response during recent geomagnetic storms and the declining phase of the current solar cycle, as well as on the interpretation of the differences in the data among the three spacecrafts, due to their orbits.

A new generation of Absolute Scalar Magnetometers (ASM) is currently flown on the LEO satellites of the ESA Swarm mission. These instruments routinely and simultaneously provide 1 Hz absolute scalar values (1pT/Hz1/2 resolution, [DC-0.4 Hz] bandwidth) and self-calibrated vector components of the magnetic field (2nT/ Hz1/2 resolution), but can also be run in a scalar burst mode, providing 250 Hz absolute scalar values ([DC-100 Hz] bandwidth). The 250 Hz scalar mode already allowed the detection of until now very poorly documented extremely low frequency whistler signals produced by lightning in the atmosphere, which have been used to investigate the ionosphere, while the 1 Hz scalar/vector mode data have successfully been used to produce scientifically relevant core field and lithospheric field models. Both ASM modes have thus now been fully validated for science applications. Here, we will report on the latest progress towards building a 12U nanosatellite (NanoMagSat), which would take advantage of a miniaturized and improved version of this instrument operating in an even more useful mode, simultaneously providing high sampling (400 Hz) absolute scalar data and self-calibrated 1 Hz vector data. Such a nanosatellite could be launched on an inclined LEO orbit (60° inclination) to complement the Swarm constellation by covering all local times at a much faster rate. Beyond this maiden mission, additional similar low-cost nanosatellites could form the basis of a future constellation of multiple high-precision nanosatellites for permanent monitoring of the Earth’s magnetic field and ionospheric environment.