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The Importance of tex2html_wrap_inline378 Drifts

The tex2html_wrap_inline378 convection of plasma is vital in understanding the large-scale convection of plasmas in the magnetosphere, the creation of unstable particle distributions and associated wave growth and particle scattering, and the motions of individual particles. Reconsider Figures 14.4 - 14.8 from the point-of-view of tex2html_wrap_inline378 drifts.

Suppose first that the solar wind electric field is directed from dawn to dusk (i.e., eastwards) or out of the paper. Then in the plasmasheet the tex2html_wrap_inline378 drift is Earthwards from the tail and sunwards from Earth, so that tail plasma is brought Earthwards, drifts around the Earth due to curvature and gradient drift, and then drifts to the magnetopause where it is lost. Similarly, plasma leaving the cusp tailward or plasma moving in the tail is convected down toward the plasma sheet, leading to cutoff distributions and a denser and thinner plasma sheet.

Notice now the effect of the solar wind electric field reversing in sign. (How could this happen? Consider the definition of tex2html_wrap_inline510 and the usual dominance of the radial or tex2html_wrap_inline512 component of the solar wind velocity.) Now all the tex2html_wrap_inline378 drift velocities are reversed and so are the corresponding convection patterns. It can now be seen that solar wind activity can be expected to have major consequences on the plasma and ``space weather'' in Earth's magnetosphere. This subject is discussed in more detail in the next lecture.

Iver Cairns
Tue Sep 14 14:46:55 EST 1999