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NASA X- (3413
MODEL STUDY OF PLASMAPAUSE
MOTION
J. M. GREBOWSKY
DECEMBER 1969
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GODDARD SPACE FLIGHT
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MODEL STUDY OF PLASMIAPAUSE MOTION
J. M.
Grebowsky
LabGratory for Atmospheric and Biological Sciences
December 1969
GODDARD SPACE FLIGHT CENTER
GreenWlt, Maryland
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CONTENTS
Page
ABSTRACT
.......................................................
iii
INTRODUCTION...................................................
1
STEA
DY
STATE MODEL ..........................................
2
TIME DEPENDENT MODEL .......................................
5
CONCLUSIONS
....................................................
8
BIBLIOGRAPHY ..................................................
9
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MODEL STUDY OF PLASMAPAUSE MOTION
INTRODUCTION
A sharp drop in the ambient electron density with increasing altitude usually
occurs at a geocentric distance of a few earth radii near the equatorial plane
(Carpenter, 1963; Gringauz, 1963; Taylor et al., 1965). This region of abrupt
change is commonly referred to as the knee or as the plasmapause while the
high density region bounded by the plasmapause is called the plasma sphere.
The origin of the knee is best explained qualitatively by a model originally
developed by Nishida (1966). In this model, under steady state conditions the
knee is the boundary between plasma that drifts always across closed geomag-
netic field lines and plasma which at some time in its mot: )n drifts onto open
field lines (i.e., field lines which extend deep into the magnetospheric tail). In
the former plasma regime (the plasmasphere) plasma escape is always prevented
by closed field lines. Outside of the plasmasphere, however, a depletion of the
ambient plasma occurs due to escape along the open field lines into interplane-
tary space.
From whistler measurements (Figure 1) it is known that the knee position
in the equatorial plane is a function of local time with its maximum geocentric
distance usually occurring in the dusk sector. On the average, when the magnetic
.,:
index K
p
increases, the plasmapause moves to smaller L coordinates (Carpenter,
1966; Taylor et al., 1968; Binsack, 1967).
The time dependent motion of the plasmapause during magnetic substorms
is best characterized by the behavior of the bulge as deduced from ground based
k^
1