Swarm

More than two year of data from ESA's Swarm constellation mission are used to derive a model of the Earth’s magnetic field and its time variation (secular variation). The model describes contributions from the core and lithosphere as well as large-scale contributions from the magnetosphere (and its Earth-induced counterpart). We use data from geomagnetic quiet times and co-estimate the Euler angles describing the rotation between the vector magnetometer instrument frame and the North-East-Center (NEC) frame. In addition to the magnetic field observations provided by each of the three Swarm satellites and alongtrack first differences we include the East-west magnetic gradient information provided by the lower Swarm satellite pair, thereby explicitly taking advantage of the constellation aspect of Swarm.

We assess the spatial and temporal model resolution that can be obtained from two years of Swarm satellite data by comparison with other recent models that also include non-Swarm magnetic observations.

The Swarm satellite constellation mission provides high precision magnetic field data and models and other observations that enable us to explore near Earth space for example in terms of in situ electron density and electric fields. On board GPS observables can be used for sounding ionospheric and plasmaspheric electron content and GPS and accelerometer data are used to derive information on thermospheric density.

Continuous data sets from LEO satellites, such as Swarm, and often combined with ground observations have been useful in developing empirical models of the temporal occurrence and local distribution of typical structures, like the expansion of the auroral oval depending on magnetic activity; or the typical climatological behaviour of plasma structures in the F region ionosphere, such as equatorial depletions or polar enhancements. Among others, these three phenomena can harm, for example, continuous radio navigation and communication (e.g., Galileo, GPS) through the development of severe ionospheric plasma gradients, e.g., during geomagnetic storms.

This paper will discuss opportunities from LEO satellites for imaging the actual state of the magnetosphere and upper atmosphere for applications in aeronomy and space weather. We will emphasize results from the Swarm mission. 

Launched on 22 November 2013, Swarm is a three-satellite constellation mapping the Earth’s magnetic and observing key geospace observables, including the electric field, current systems, auroras, as well as the neutral environment.  The scientific production based on the first two years  of Swarm data exploitation has been nothing short of overwhelming. Swarm is bringing to ESA and to the worldwide community a vast amount of new science, ranging from the deep interior (i.e. the outer core), through the mantle, lithosphere and oceans, via the thermosphere and the ionosphere all the way out to the magnetosphere. The mission also provides excellent opportunities to study the coupling mechanisms that exist between virtually all these parts of ‘system Earth’.

At the base of the mission success lies the fact that the mission delivers unprecedented observations that through modelling and interpreation improve our understanding of the Earth’s interior as well as the near Earth electro-magnetic environment. The unprecedented high-accuracy and high spatial resolution measurements of the strength, direction and time variations of the magnetic field, complemented by precise navigation, accelerometer and electric field measurements, provide the required observations to address the scientific objectives.

The three satellites fly in a constellation. Swarm Alpha and Charlie are orbiting almost next to each other at a distance of about 150 km at the equator and Charlie is approximately 10 seconds delayed relative to Alpha. At the start of the science phase they were injected at an altitude of 462 km and an inclination of 87.35°, in naturally decaying orbits. Swarm Bravo started in a higher orbit at 510 km with an inclination of 87.75°. This causes a relative drift between Alpha/Charlie and Bravo resulting in a local time difference of about 6 hours in the third year of the mission. Different objectives of the mission may benefit more during different phases of the constellation. 

This contribution discusses all top-level mission management aspects of the missions, ranging from the overall mission status, through the flight operations and data product generation, to the status of the mission exploitation. It also includes a broader perspective on the evolution of the mission, up to and beyond its nominal lifetime.

Large-amplitude filamented mangetic field signatures are reported on Swarm satellites at high latitudes on the dayside during periods of northward IMF. The multiple Swarm satellites enable an investigation of the spatio-temporal structure of the magnetic field signatures observed in the vicinity of the cusp during such solar wind forcing.  The perturbations are observed at amplitudes of ~10-100 nT or more in the 0.1-5 Hz frequency range in the frame of the satellites on 10s timescales between passes of Swarm A and C. The spatio-temporal coherence is ordered by magnetic latitude across the cusp, suggesting different dynamical processes are operating including the excitation of large amplitude Alfven waves. The period under study is extremely quiet as characterised by ground-based magnetometers, suggesting that these large amplitude fluctuations occur on small spatial scales. Nonetheless they are expected to have significant implications for field-aligned current (FAC) calculations, especially if FAC data products are generated using lower-cadence data sets. Despite the relative quiet of the global magnetosphere as characterised by the ground-based magnetometers, the strength of the magnetic perturbations suggest that the Alfven waves and currents generated during this period can  play an important role in magnetosphere-ionosphere coupling and energy transport. This study aims to examine and characterise these filamentary structures in the wider context of quiet-time northward IMF dynamics, to quantify their impact on FAC data products and to suggest guidelines for FAC calculations in the presence of these disturbances. We further present a new paradigm which may be able to explain the generation of these magnetic disturbances in the cusp region based on excitation arising from dynamics following-high latitude lobe reconnection tailward of the cusp. 

The Swarm satellites are unique in their ability to combine precise, multi-point observations of magnetic field flucutations stemming from ionospheric sources with simultaneous measurements of electric fields and related plasma properties.  Most importantly, the combination of  B and E measurements allows one to estimate the integrated ionospheric conductivity below the satellites along with the net dissipation of electromagnetic energy within the conductive layer.  This talk will provide an overview of the electrodynamic properties of the high-latitutde ionosphere as seen by Swarm, including the dependence of dissipative structures on solar illumuniation and scale size, and their relation to auroral forms.