Making a Connection

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Science  25 Jan 2002:
Vol. 295, Issue 5555, pp. 589
DOI: 10.1126/science.295.5555.589a

Earth is protected from the solar wind, a stream of highly energetic ions and electrons, by its magnetic field. Some particles do, however, penetrate this shield during magnetic storms, causing disruption to satellites, communications, and power supplies, as well as generating striking auroral displays at high latitudes. These penetrations are believed to occur by means of a process called “magnetic reconnection,” in which the geomagnetic field and the interplanetary magnetic field short-circuit, providing easy access to the magnetosphere along the open field lines. Many aspects of this process remain unclear, and advances are hampered by the fact that the reconnection process is difficult to observe.

Collisions between particles cannot be the main driving force for reconnection, because the solar wind and the magnetosphere are two very sparse plasmas. Anomalous resistivity—the scattering of particles through interaction with wave fields—has been implicated, but analytical resistivity estimates were too low to account for observations. Watt et al. have simulated wave-particle interactions caused by ion-acoustic instabilities. They conclude that the previous analytical estimates may have been too low by three orders of magnitude, because quasi-linear effects were assumed to be weak. Other instabilities that cause anomalous resistivity may have been similarly underestimated. The authors caution that their one-dimensional simulations cannot capture all of the processes that occur in the real three-dimensional system. Nevertheless, the results suggest that magnetic reconnection may be easier to achieve than previously thought, bringing theory more in line with observation. — JU

Geophys. Res. Lett., 10.1029/2001GL013451.

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