Charged particles from space are often trapped by the Earth’s magnetic field. The particles bounce back and forth between the two hemispheres of the planet along the field lines like beads on a string, creating the vibrant auroras that illuminate the night sky at high latitudes. These field-aligned currents (FACs) have been of interest to scientists studying space weather phenomena since they were discovered in the late 1960s.
Until now, everything scientists have learned about these intense currents has come from observations from lone satellites, which are subject to two “crippling assumptions,” according to the authors of a new study: that the currents are static and that they have a simple, sheet-like geometry.
To find out if those assumptions are warranted, Lühr et al. used data from the early days of the European Space Agency’s Swarm constellation mission to observe how FACs of various sizes change over time. The authors looked at measurements collected during the first 3 months after the satellites launched in November of 2013, when the three spacecraft were still relatively close together.
They found that small-scale currents, extending up to 10 kilometers, are highly variable. Smaller-scale FACs remain stable only for periods up to 10 seconds, and their spatial structure could not be determined. Large-scale FACs, which extend up to 150 kilometers, were stable for up to 60 seconds and were roughly 4 times longer along their longitudinal axis than they were wide, confirming their sheet-like structure. The study shows that large FACs are likely both stable and sheet-like, meaning that single-satellite estimates of larger currents at auroral latitudes are relatively accurate. (Geophysical Research Letters, doi:10.1002/2014GL062453, 2015)
—Kate Wheeling, Freelance Writer
Citation: Wheeling, K. (2015), New insights into currents in Earth’s magnetic field, Eos, 96, doi:10.1029/2015EO029795. Published on 18 May 2015.