2:00pm - 2:20pm
Keynote: A Swarm Perspective on M-I-T Coupling
Institute for Space Sciences, Bucharest, Romania
With its multi-point observations of the magnetic field, electric field, and neutral atmosphere, Swarm provides an unprecedented platform to investigate the ionosphere (I) and thermosphere (T), their mutual interaction, as well as their further coupling to the magnetosphere (M). This talk will provide a concise overview of M-I-T investigations relevant to Swarm, will present a selection of Swarm results, and will address further Swarm prospects to contribute to the field. The talk will emphasize specific assets of the mission, like the coordination with ground stations, conjugate observations with other space-based platforms (e.g. Cluster, e-POP, DMSP), or the possibility to explore systematically the longitudinal dimension of M-I-T coupling and its potential impact on auroral research. Last but not least, the talk will touch also the upcoming Swarm constellation manoeuvres, of immediate interest to all scientific communities involved in the mission.
2:20pm - 2:35pm
Longitudinal Gradients in Ionospheric Currents as Deduced with the Method of Spherical Elementary Current Systems
1Finnish Meteorological Institute, Finland; 2University of Oulu, Finland
We study how the method of Spherical Elementary Current Systems (SECS) can be applied to Swarm magnetic data in order to create new data products estimating electric currents in the auroral ionosphere. Our aim is to release a validated set of these data products for open test use during the year 2017. Exact content of this data set and the methodology used to create it will be described in the presentation. We show some results from comparisons of our products with ground-based ionospheric observations by the MIRACLE network and with the already existing Swarm L2 current products. Pros and cons of the Swarm-SECS approach in statistical studies will be discussed with the focus in the optimal spatial resolutions that the method can provide for different current components. As an example of harvesting the new data set we demonstrate how the pair of Swarm A and C satellites can be used to study longitudinal gradients in horizontal currents and their connection with the intensity of field-aligned currents in different magnetic local time sectors.
2:35pm - 2:50pm
Evidence That Field-Aligned Currents Do Not Saturate
1Virginia Tech, United States of America; 2GFZ German Research Centre for Geosciences, Potsdam, Germany
For well over a decade there have been several studies that have shown evidence that the ionospheric, polar cap electric potentials exhibit a "saturation" behavior in response to the levels of the driving by the interplanetary magnetic field (IMF) and electric field (IEF) in the solar wind. This saturation behavior is manifested in the potential versus driving function as a nearly linear response at low driving levels, followed with a roll-over and leveling off as the strength of the driving increases. Several different theoretical explanations have been presented for this behavior, yet so far no direct observational evidence
has existed to confirm one mechanism over another. In most saturation theories the interaction of the field-aligned currents (FAC) with the coupled, solar wind/magnetosphere/ionosphere system has a role in this potential saturation; even so, the behavior of the FAC in response to the driving of the IEF has not been investigated as thoroughly as the electric potentials.
In order to resolve the question of whether or not the FAC also exhibit saturation, we have processed the magnetic field measurements from the Oersted, CHAMP, and Swarm missions, spanning more than a decade, in order to determine how the total FAC responds to the solar wind. We will present evidence showing that the field-aligned currents have a response to the IEF that remains highly linear well beyond the level at which the electric potentials begin to roll over. It appears that the currents do not saturate. On the other hand, at very extreme levels of driving, as seen with IMF magnitudes over 25 nT, the number of such events are so sparse that it is difficult to provide an unequivocal determination that the total current does level off at some upper level.
2:50pm - 3:05pm
Unified Global and Local Perspectives on High-latitude Ionospheric Electrodynamics
1University of Colorado Boulder, United States of America; 2GFZ Potsdam, Germany
By combining Swarm data with other global geospace observations (e.g., Iridium/AMPERE, SuperMag, and SuperDARN) with the help of a comprehensive data assimilation and inverse procedure (namely the Assimilative Mapping Ionospheric Electrodynamics (AMIE) [Richmond and Kamide, 1988] and the latest develoment under AMIE Nextgen [e.g., Matsuo et al., 2015, Cousins et al., 2015]), we can unravel how fine-scale transient features of high-latitude ionospheric electrodynamics are embedded in large-scale structures. Such an approach provides unified global and local perspectives that facilitate interpretation of localized phenomena, such as cusp neutral mass density enhancements in response to localized heating, in the global context of magnetosphere-ionosphere-thermosphere coupling, and extends the utility of Swarm data for space science research
Richmond, A. D. and Y. Kamide (1988), Mapping electrodynamic features of the high-latitude ionosphere from localized observations: technique, J. Geophys. Res., 93, 5741-5759.
Matsuo, T., D. L. Knipp, A. D. Richmond, L. Kilcommons, and B. J. Anderson (2015), Inverse procedure for high-latitude ionospheric electrodynamics: Analysis of satellite-borne magnetometer data, J. Geophys. Res, 120, 5241-5251, doi:10.1002/2014JA020565.
Cousins, E. D. P., T. Matsuo, and A. D. Richmond (2015), Mapping high-latitude ionospheric electrodynamics with SuperDARN and AMPERE, J. Geophys. Res., 120, 5854-5870, doi:10.1002/2014JA020463.
3:05pm - 3:20pm
Poynting Flux Estimation from Electric and Magnetic Field Data of the Swarm Constellation
1Korea Astronomy and Space Science Institute, Republic of Korea; 2Department of Astronomy and Space Science, University of Science and Technology, Daejeon, Korea; 3GFZ German Research Centre for Geosciences, Potsdam, Germany; 4Faculty of Sciences, University of Potsdam, Potsdam, Germany; 5Department of Physics and Astronomy, University of Calgary, Calgary, Alberta, Canada
In space science Poynting flux represents the direction and magnitude of electromagnetic energy flow, which is an important clue to reveal the energy source of many geophysical phenomena. In spite of the long history of electric and magnetic field measurements on Low-Earth-Orbit (LEO) satellites, however, only a few studies could estimate Poynting flux at those altitudes, mainly because of difficulties in simultaneous and precise observations of electric and magnetic fields. In this presentation we investigate Poynting flux deduced from Swarm observations at mid- and high-latitude regions near 500 km altitudes. First, the statistical distribution of Poynting flux at nighttime mid-latitude regions is presented and discussed in the context of medium-scale traveling ionospheric disturbances (MSTIDs). Second, statistical distribution of high-latitude Poynting flux is investigated, and the results are compared with previous satellite observations conducted at much higher magnetospheric altitudes. Finally, ionospheric reflection coefficients are estimated from the Poynting flux and Alfven velocity data obtained by the Swarm constellation.
3:20pm - 3:35pm
Birkeland Current Boundary Flows
1University of Calgary, Canada; 2Athabasca University, Canada; 3Finnish Meteorological Institute
Intense ion velocity spikes in the northern night-side auroral zone are measured during quiet geomagnetic conditions by the Swarm satellites around 500 km altitude. These velocity spikes, exceeding 1 km/s in over 50% of orbits measured, range from 20-100 km in latitudinal thickness and reach a maximum at the boundary between upward and downward field-aligned current. On average they represent a potential difference of approximately 3 kV between the R1/R2 currents. This boundary also separates different regions of electron temperature and meridional flow, and is associated with ion upflows and anisotropic heating. Both dawnward and duskward velocity field spikes are observed, including some oppositely-directed pairs bounding regions of upward field-aligned current. Coincident ground-based observations place ion velocity spikes adjacent to auroral arcs, embedded in the auroral electrojets. Previous literature has focused on fast flows occurring in regions of relative low conductivity surrounding auroral arcs, typically during geomagnetically active conditions, and does not address the occurrence frequency of these events. We show ion velocity spikes to be a persistent and ubiquitous property of the electrodynamics of quiet time R1/R2 current closure near midnight.