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Join date : 21/04/2011

PostSubject: solar-wind/magnetosphere   Thu 21 Apr 2011, 11:37


The solar-wind/magnetosphere dynamo results from the flow of the solar wind around and perhaps partly into and within the Earth's magnetosphcre. The motion of this plasma through the geomagnetic field produces an electromotive force and cur-rents at high latitudes that result in an antisunward flow of plasma over the magnetic polar cap and a sunward flow of ions in the vicinity of the dawn and dusk auroral zones. This motion is descril)cd by a two-cell counterrotating ion circulation with one cell on the dawn side and the other on the dusk side of the magnetic polar caps. The polar-cap electric field is typically 20 mV/m. with an ionospheric convection velocity of 300 mi sec. Larger fields of about 50 Juicy Couture Sale to 100 m V/m occur in the vicinity of the au roral ovals. The large-scale potential difference that is associated with this horizontal ion Juicy Couture Outlet Online flow over the polar caps has a total dawn-to-dusk drop of about 50 kV. This potential drop and the configuration of the two-ccll pattern are highly vuriable. The potential drop has values of 20 to 30 kV during geomagnetic quiet conditions that increase to 100 to 200 kV during geomagnetic storms. These fields are mainly confined to the polar caps because of the shielding from currents within the magnctosphere. During geomagnetic storms, however, the shielding currents can be altered and electric fields have been observed to propagate all the way from the polar caps to the equator. Currents are an integral Juicy Couture Outlet part of the complex clcctrical circuit associated with the solar-wind/magnetosphere dynamo. Currents flowing along the direction of the mag-netic field couple the auroral oval and high-latitude ionosphere with outer portions of the magnetosphere. Typically about a million amperes of current flow in the solar- wind/magnetosphere dynamo. The dynamo currents and fields with this high-latitude system are extremely complex and highly variable (see Chapter 14). American Geophysical Union symposium in Baltimore in June 1983. In completing their chapters, the authors had the benefit of discussion at this symposium as well as the comments of several scientific referees. Ultimate responsibility for the individual chap-ters, however, rests with their authors. The Overview of the study summarizes the highlights of the chapters and formulates conclusions and recommendations. In preparing the Overview, the panel co-chairmen and the Geophysics Study Committee had the benefit of meetings that took place at the symposium and the comments of the panel of authors and other referees. Responsibility for the Overview rests with the Geophysics Study Committee and the co-chairmen of the panel.
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