ESA Cluster Satellites: New Insights into Polar Aurorae
15.02.2007 - Other
New results obtained thanks to ESA's Cluster satellites provide a new insight into the source of the difference between the two types of electrical circuits currently known to be associated to the auroral arcs.
Ancient observations from 2004 showed that these electric potential structures are mainly of two types - symmetric (U-shaped) or asymmetric (S-shaped).
Previously, scientists believed that they were occurring in different geographical regions. In short, it was thought that:
- U-shaped structures were found at a plasma boundary between the so-called 'central plasma sheet', situated in the magnetotail at equatorial latitudes, and the 'plasma sheet boundary layer', an adjacent area located at higher latitudes.
- S-shaped structures were found at the boundary between the 'plasma sheet boundary layer' and the polar cap, further up in latitude.
New observations from ESA's Cluster satellites show that it's not so: both kinds of structures were observed in the same geographical area within a very short timeframe. Measurements showed that the plasma density and the associated currents and fluxes of particles decreased significantly in the plasma sheet boundary layer. In this way this boundary ended up in resembling the asymmetric conditions typical of the polar cap boundary.
Scientists interpreted that the 'reconfiguration' from a U-shaped to a S-shaped potential structure, and of the associated electric circuits that sustain the auroral arcs, reveal the change in the plasma conditions on the two sides of the boundary.
The results represent a major step forward in understanding the auroral electrical circuits.
