Thin current sheet-like structure of Earth’s magnetosphere could help understand magnetic reconnection

Scientists have shown that when solar wind compresses Earth’s magnetosphere into a thin current sheet-like structure – at that point it is possible to study magnetic reconnection – a phenomenon known to have impact on Earth’s atmosphere and weather.

Scientists explain that while Earth’s motion could give a feeling of a calm, pristine movement, the reality is completely different. The near-Earth space environment is dangerous and dynamic. During solar storms the solar wind can compress the Earth’s magnetic field which in turn causes rearrangement and reconnection of magnetic field around Earth that in turn shoots hot, dense plasma back toward the Earth.

Processes like these are commonly referred to as space weather. Because of the effect that these space-based disruptions can have on key elements of our modern society, such as telecommunication systems and power grids, obtaining a good understanding of these processes is just as essential as understanding ground-based weather.

A major challenge in understanding magnetic reconnection in the Earth’s magnetosphere has been the difficulty in resolving the smaller kinetic-scale processes in satellite observations. NASA’s Magnetospheric Multi-Scale (MMS) spacecraft, however, recently made it possible to make detailed studies of this previously unseen micro-scale physics.

Scientists at the U.S. Naval Research Laboratory (NRL) in Washington, D.C. have been using MMS data to study the micro-scale physics that occurs in the Earth’s magnetotail, a thin portion of the magnetosphere that is illustrated in Figure 1. The magnetotail is formed when the Earth’s magnetosphere is compressed by the solar wind into a thin current sheet, creating an ideal location to study magnetic reconnection.

NRL scientists recently made the first observation of plasma waves driven by highly sheared electron flows (velocity shear) in one of these compressed current sheets. The velocity shear is created in the current sheet when a localized electric field oriented perpendicular to the background magnetic field arises as the current sheet is compressed. These waves are a rich source of local enhanced diffusivities, which can trigger the magnetic reconnection process.

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