Eos, Transactions American Geophysical Union

Magnetosphere

Authors


Abstract

Research on the terrestrial magnetosphere, above 500 km, continues to focus on how energy gets from the solar wind into the magnetosphere and how it circulates through the magnetosphere. The prime candidate for energy coupling has long been magnetic merging in which the magnetic field that the solar wind carries from the Sun merges with the geomagnetic field. (The result couples the ionosphere, above 60 km, to the solar wind by magnetic field lines that act both as elastic bands, stretching against the motion of the wind and extracting energy from it, and as current conductors, electrically conveying the extracted energy to the ionosphere.)

Only a decade ago, the first direct evidence of merging was uncovered in the form of fast, magnetically driven flows at the magnetosphere's sunward boundary. Narrow and brief, such flows are elusive, rendering synoptic studies difficult. On the other hand, distinctive, common wiggles in the magnetic field near the boundary, called “flux transfer events” (FTE), are suspected of being proxy merging signatures. The problem has been that to learn about merging from FTEs requires a physical model connecting them. A new FTE model postulates that impulsive merging launches tube-like surges along the boundary and perturbs the field to some distance away. This model, independently proposed by two leading theorists, seems to satisfy all observational constraints (untrue of earlier attempts), and thereby seems to bring the field much closer to exploiting FTE data.

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