TBA

Magnetic reconnection occurs continuously along long X-lines at the Earth’s magnetopause. The maximum magnetic shear model provides accurate predictions for the locations of these long X-lines for a wide range of upstream solar wind conditions. One of the more perplexing observational results is that these X-lines appear to be stationary, even on the near-flank magnetopause in the presence of significant magnetosheath plasma bulk flow. An alternate possibility is that X-lines form in the location predicted by the maximum magnetic shear model but then immediately propagate with the magnetosheath plasma bulk flow away from this location. If the X-line reformation cadence is high enough and some other conditions are valid, then these multiple propagating X-lines could appear as a single quasi-stationary X-line at the location predicted by the maximum magnetic shear model. Magnetospheric multiscale observations are used to perform initial tests of this alternate possibility. Results from these initial tests show that there may be multiple X-lines near the predicted location of the X-line, and therefore this alternate possibility may have merit. This alternate possibility may have implications for the magnetospheric cusps. Magnetic reconnection at the magnetopause produces distinct energy-latitude ion dispersion features in the cusps. Multiple reconnection X-lines may produce overlapping dispersion features depending on how they are formed. Therefore, under the right solar wind conditions, there may be many instances of overlapping dispersion features. Observations from the Tandem Reconnection and Cusp Electrodynamics Reconnaissance Satellites (TRACERS) are used to investigate this possibility.

Alfven waves, named after the Nobel laureate Hannes Alfven, are a fundamental mode in magnetized plasmas. It has long been established that they play a key role in the energy circulation of the magnetosphere-ionosphere (M-I) coupling system. However, their dissipation on meso- and small-scales is much less well understood. Here, we examine how Alfven waves drive several common meso-scale structures, including the auroral arcs, auroral beads, and the magnetospheric cusp. We find that Alfven waves, although being the common energy source, are dissipated differently among these structures. In the auroral arcs, Alfven waves power a quasi-static parallel electric field that accelerates ions away from and electrons toward the ionosphere. In the auroral beads, electrons are accelerated directly by the wave’s own parallel electric field. In the cusp, Alfven waves significantly energize the outflowing ions, presumably through perpendicular heating. These distinct energy conversion processes we have unveiled are important in understanding the meso-scale M-I coupling on Earth and other planets. Our results also raise important questions for future studies: How are these Alfven waves generated? What additional dissipation mechanisms may be operating? Why are Alfven waves dissipated differently, and what are the controlling factors?

Alfvén waves, named after the Nobel laureate Hannes Alfvén, are a fundamental mode in magnetized plasmas. It has long been established that they play a key role in the energy circulation of the magnetosphere-ionosphere (M–I) coupling system. However, their dissipation on meso- and small-scales is much less well understood. Here, we examine how Alfvén waves drive several common meso-scale structures, including the auroral arcs, auroral beads, and the magnetospheric cusp. We find that Alfvén waves, although being the common energy source, are dissipated differently among these structures. In the auroral arcs, Alfvén waves power a quasi-static parallel electric field that accelerates ions away from and electrons toward the ionosphere. In the auroral beads, electrons are accelerated directly by the wave’s own parallel electric field. In the cusp, Alfvén waves significantly energize the outflowing ions, presumably through perpendicular heating. These distinct energy conversion processes we have unveiled are important in understanding the meso-scale M–I coupling on Earth and other planets. Our results also raise important questions for future studies: How are these Alfvén waves generated? What additional dissipation mechanisms may be operating? Why are Alfvén waves dissipated differently, and what are the controlling factors?