scispace - formally typeset
Search or ask a question
Journal ArticleDOI

Observations of irregular structure in thermal ion distributions in the duskside magnetosphere

01 May 1970-Journal of Geophysical Research (John Wiley & Sons, Ltd)-Vol. 75, Iss: 13, pp 2481-2489
TL;DR: In this article, the authors measured distributions of hydrogen and helium thermal positive ions in duskside magnetosphere and showed that the irregular structure and position indicated by measured distribution of hydrogen, helium, and other ions in the magnetosphere can be inferred.
Abstract: Plasmapause irregular structure and position indicated by measured distributions of hydrogen and helium thermal positive ions in duskside magnetosphere

Summary (3 min read)

INTRODUCTION

  • Since the first evidence obtained by Gringauz [1963] and Carpenter [1963] that a distinct envelope of thermal plasma surrounds the earth in the form of the plasmasphere, considerable effort has been directed toward obtaining additional data sufficient to describe the global nature of this region.
  • Extensive ground based whistler studies [Carpenter, 1966] have revealed a pronounced diurnal asymmetry in the radial extent of thc plasmapause as observed in the equatorial plane.
  • Direct measurements of the ion composition obtained from OGO 1 and 3 reported earlier have indicated that the plasmasphere is elongated in the dusk sector, relative to other local time positions in both the dayside and nightside magnetosphere [Taylor et al., 1965] [ Brinton et al., 1968] .
  • Plasma probe results from IMP-2 [Binsack, 1967] also suggest an increase in the average L position of the plasmapause toward the dusk meridian, although as was the case with the OGO-1 ion composition results, the data points available in the dusk region are limited.
  • In addition, the longterm variation in the average position of the plasmapause, as observed during the decline of solar cycle 19 and the emergence of solar cycle 20, is examined.

Description of the Experiment

  • 'The ion composition experiment on OGO-3 consists of a Bennett radio frequency mass spectrometer which measures the ambient distributions of positive ions in the mass range 1-45 AMU.
  • The ion spectrum scan rate is 64 seconds, which provides a separation between successive samples of a given ion of about 250 km (or O.1L) for satellite trajectories considered in this paper.
  • DF;termination of the absolute value of the limiting sensitivity is in n3rt dependent upon the type of processing techniques used for the reduction of the data.
  • Accordingly, these data do not exhibit the ram-wake modulation associated with dynamic attitude-velocity chances, and thus the rapid fluctuations inherent in the distribution of the ambient plasma may be examined in detail.
  • Further details of the ion composition experiment have been included in papers by Brinton et al. [1968] and Taylor et al. [1965] .

Selection of Ion Profiles

  • The data to be discussed were obtained during the period June 1966 through August 1967.
  • The detailed ion profiles presented are limited to the period June 17, 1966 through July 23, 196b when OGO-3 was attitude controlled.
  • An example of the H+ and fie + distributions observed in the plasmasphere under conditions for which the plasma-pause is observed as a sharply defined boundary is given in Figure 2A .
  • The parallelism between the II+ and Iie+ distributions, with n(H+)/n(fie+) = 100 is also typical of much of the data.
  • In crossing is followed by periods of significant plasma recovery, wherein I n(H+) may rise from the threshold concentration (5 ions/cm 3) to concentrations as large as 500 ions/cm .

' Comparison of Midnight and Dusk Results i

  • In Figure 5 a pair of H + distributions obtainer'. on July 3, 1966, curing low to moderate magnetic activity (Kp-24 = 2+), reveal a considerable difference in the position of the plasmapause observed in the dusk and midnight local time sectors.
  • In general, the OGO-3 and IMP-2 results show the boundary to be displaced outward from the earth.
  • The IMP data were obtained during still lower solar activity, at solar minimum, while the OGO data were taken at higher solar activity, during the upswing of solar cycle 20.
  • It was, of course, not possible to compare these data sets under identical magnetic conditions.

DISCUSSION AND INTERPRETATION

  • The OGO-3 ion results are unfortunately of insufficient temporal and spatial resolution to completely identify the characteristics or what may be a rather permanent asymmetry in the average position of the plasmapause in the afternoon-dusk sector.
  • The close comparison of results obtained within the spacing of but a few hours on the same day and under quiet magnetic conditions, however, shows that this anomalous region is indeed persistent in the form of a significant plasmasphere expansion accompanied by regions of structured plasma recovery.
  • The contraction of the plasmasphere bulge during periods of enhanced magnetic activity is also consistent with the magnetospheric models decribed above.
  • Such fluctuations in the wind could enhance the turbulent region and explain the pronounced structure which the authors frequently observe in the dusk-side data.
  • The evidence from their data, however, suggests that the plasma observed just above the initial plasmapause, in the region of pronounced plasma fluctuations, is identical in nature (within the limits of their detection scheme) to the plasma measured within the plasmasphere itself.

Long Term Variability in the Plasmapause Location

  • The comparison of the average position of the plasmapause observed in 1963 by Carpenter with their results, for similar conditions of magnetic agitation (Kp = 2-4), indicates that in 1966-67 the plasmasphere may have expanded to an average position which is about 1.5-21, more distant than the average position measured earlier, nearer the minimum of solar cycle 19.
  • The IMP results observed at the lowest solar activity levels, however, do show the boundary to be a higher L positions than the vlf results, for all local times observed.
  • Too little is known about the significance of the timing and spatial extent of magnetic storms to permit a comparison of data taken under 'identical' conditions.the authors.
  • Thus it is possible that the data sets have been averaged too coarsely and are perhaps biased toward either quiet or disturbed conditions.
  • It is clear that the mechanisms controlling the distribution of the magnetospheric thermal plasma are complex and that while gross features seem to persist, caution should be exercised in describing either the 'average' profile, or position of the plasmapause.

Did you find this useful? Give us your feedback

Content maybe subject to copyright    Report

General Disclaimer
One or more of the Following Statements may affect this Document
This document has been reproduced from the best copy furnished by the
organizational source. It is being released in the interest of making available as
much information as possible.
This document may contain data, which exceeds the sheet parameters. It was
furnished in this condition by the organizational source and is the best copy
available.
This document may contain tone-on-tone or color graphs, charts and/or pictures,
which have been reproduced in black and white.
This document is paginated as submitted by the original source.
Portions of this document are not fully legible due to the historical nature of some
of the material. However, it is the best reproduction available from the original
submission.
Produced by the NASA Center for Aerospace Information (CASI)

^^ I^`-
-
-
F
^
_ `` ~ { !^
V
-^
_
,.
.
^.
.^
^^^
X-621-69-51$
.
PREPRINT °
^^^^ rl^ .^- ^,3?
-:
OBSERVATIONS^OF IRREGULAR
= L -
-
^^
STRUCTURE IN '^IERM^L^ 101
DISTRIBI^-TI^JN'S IN THE DUSK-SIDE
MAGNETOSPHERE
I^,. -^
. TAY^oR
.,
W, C. BRINTOI+^
A. ^^ DESHMU[CH
I
^ECEMBER^1969
ems.
^ _
^^^
`^' `-^'^ 1"a,c'" -'^
^, ^_ . ^tui,^^y us ,
'^
I'
-
^
^3a
^^-
_
_^
t Y
^`'
y^^
-
^
0 Z,
--^-
GBDDA^D SPJ^CE F^.I^^^^
TER ._
-
_^
-
-^
6REENBE^T, ^ ^ARXLAt^-^
.
''', _ ,
- ;
-
N^0 -12 920
-
^
UCC[.[101
M[[Ill
s
-
0
^
OD[I
=
^
IIAY[[I
^^,
INA.A R A TMl[ 011 AD MUM• AI
lewr[oo11r1
^
r T
i
_
.,
.`.
:^^

^^.
X-621-69-519
t
%.
^:.
.}
^.
OBSERVATIONS OF IRREGULAR STRUCTURE IN
Tf-iERMAL ION DISTRIBUTIONS IN Tf->E
DUSK-SIDE MAGNETOSPI^RE
11. A. Taylor, fi. C. Brinton
Laboratory for Atmospheric and Biological Sciences
Goddard Space Flight Center
Greenbelt, Maryland 20771
and
A. R. Deshmukh
Aero Geo Astro Company
Belts^^ille, Maryland 20705
December19^9

OBSERVATIONS OF IRRECUI.AR STRUCTURE IN
THERMAL ION DISTRIBUTIONS IN TIC
DUSK-SIDE MAGNE"TOSPHERE
H. A. Taylor, H. C. Brinton
and
A. R. Deshmukh
ABSTRACT
Direct measurements of the distributions of the thermal positive
ions H
+
and He
+
in the magnetosphere reveal a distinct variability in
the position and structure of the plasr^^apause. Such variability is
observed to be most pronounced in the afternoon-dusk local time sector
,:
and is indicative of magnetospheric irregularities in the same region.
As the OGO-3 satellite made progressive dusk-side (1500 - 1900 L.T.)
and night-side (2200 - 0100 L.T.) passes during June-July 1966, the
dusk-side plasmasphere was observed to exhibit an outward expansion or
.
bulge, accompanied in some cases by considerable fine structure. In
particular, the plasmapause was observed at L positions as distant as
L = 7-8 in the afternoon-dusk sector, in contrast to positions near
L = 5-6 observed near midnight on the same day and at comparable
'
levels of moderate magnetic activity (Kp < 3). Within the bulge and
just above the initial plasmapause structured plasma recoveries are
observed, wherein n(H
+
) returns to concentrations of the order of
SO-100 ions/cm
3
over intervals of 0.5 - 1.5L. Both the dusk-side
i

,1
bulge and fine structure are observed to persist during periods of
enhanced magnetic activity (Kp = 4-6). The above variability is
superimposed on an average diurnal distribution of the plasmapause
which is similar in shape to that deduced from whistler data during
1963, although the 1966-67 results indicate that the plasmapause may
have expanded to a position generally more distant by about 1.5 - 2L.
The evidence of the plasma bulge and the associated plasma fluctua-
tions, is generally consistent with magnetospheric convection models
proposed by Nishida and by Brice. These models predict both a
similar local time asymmetry in the plasmapause radius, and a dusk-
side region of plasma turbulence, generated at the interface of
closed, co-rotating field lines and field lines which through con-
vection are connected to the n^agnetotail, and thereby provide a plasma
^
escape mechanism.
_^^
ii

Citations
More filters
Journal ArticleDOI
TL;DR: In this paper, an empirical model of equatorial electron density in the magnetosphere covering the L range 2.25-8.9043 was presented for application to the local time interval 00-15 MLT, and a way to extend the model to the 15-24 MLT period is presented.
Abstract: Attention is given to an empirical model of equatorial electron density in the magnetosphere covering the L range 2.25-8. Although the model is primarily intended for application to the local time interval 00-15 MLT, a way to extend the model to the 15-24-MLT period is presented. The model describes, in piecewise fashion, the 'saturated' plasmasphere, the region of steep plasmapause gradients, and the plasma trough. Within the plasmasphere the model profile can be expressed as logne - Sigma-xi, where x1 = -0.3145L + 3.9043 is the principal or 'reference' term, and additional terms account for: a solar cycle variation with a peak at solar maximum; an annual variation with a December maximum; and a semiannual variation with equinoctial maxima.

787 citations

Journal ArticleDOI
TL;DR: The morphology and dynamics of the plasmasphere vary with local time and with geomagnetic conditions as mentioned in this paper, and can be understood in terms of a time-varying convection electric-field model of the magnetosphere.
Abstract: The characteristic morphology and dynamics of the plasmasphere vary with local time and with geomagnetic conditions. On the nightside the plasmapause position changes predictably with changing magnetic activity. Once established at a specific L-shell value, the steep density gradient on the nightside corotates into the dayside, where filling from the ionosphere takes place. In the duskside bulge region the characteristic density profile inside the plasmapause displays a smooth decrease proportional to 1/R to the fourth power where R is radial distance. Plasmasphere morphology and dynamics can be understood in terms of a time-varying convection electric-field model of the magnetosphere that includes the bulge region as part of the main circulation pattern of the plasmasphere.

336 citations

Journal ArticleDOI
TL;DR: The Global Core Plasma Model (GCPM) as discussed by the authors is an attempt to assimilate previous empirical evidence and regional models into a continuous, smooth model of thermal plasma density in the inner magnetosphere.
Abstract: Over 40 years of ground and spacecraft plasmaspheric measurements have resulted in many statistical descriptions of plasmaspheric properties. In some cases, these properties have been represented as analytical descriptions that are valid for specific regions or conditions. For the most part, what has not been done is to extend regional empirical descriptions or models to the plasmasphere as a whole. In contrast, many related investigations depend on the use of representative plasmaspheric conditions throughout the inner magnetosphere. Wave propagation, involving the transport of energy through the magnetosphere, is strongly affected by thermal plasma density and its composition. Ring current collisional and wave particle losses also strongly depend on these quantities. Plasmaspheric also plays a secondary role in influencing radio signals from the Global Positioning System satellites. The Global Core Plasma Model (GCPM) is an attempt to assimilate previous empirical evidence and regional models for plasmaspheric density into a continuous, smooth model of thermal plasma density in the inner magnetosphere. In that spirit, the International Reference Ionosphere is currently used to complete the low altitude description of density and composition in the model. The models and measurements on which the GCPM is currently based and its relationship to IRI will be discussed.

322 citations

Journal ArticleDOI
TL;DR: A quick reference guide to the plasmasphere can be found in this article, where a series of equatorial density profiles is shown to illustrate the reduction of plasmapause radius during brief periods of increased disturbance and the recovery of the plasosphere by various processes, particularly by filling from the underlying ionosphere.
Abstract: Recent research on the structure and dynamics of the magnetospheric thermal plasma indicates that the vast region above an altitude of ∼1000 km rivals the underlying ionosphere in complexity and that it is coupled to the lower region in complicated, physically important ways. An example involves the relation of the electron content of magnetospheric tubes of ionization to the electron content of the regular ionosphere. Tube volume between ∼1000 km and the magnetic equator varies rapidly over a relatively small range of tube end point latitudes, which gives rise to correspondingly rapid variations with latitude in coupled effects that involve interchange of ionization between the upper and lower regions. In the past, some correlative studies involving the plasmapause have been hindered by lack of information concerning (1) the unsteady nature of the process by which the disturbed-time plasmapause profile is established and (2) the fact that at most times and at most locations the plasmasphere-plasmapause system is in a state of recovery. A series of equatorial density profiles is shown to illustrate the reduction of plasmapause radius during brief periods of increased disturbance and the recovery of the plasmasphere by various processes, particularly by filling from the underlying ionosphere. A number of research results are presented as part of a ‘quick-reference guide’ to the plasmasphere. To the ionospheric observer, the plasmapause should appear to have a complex but generally predictable geometry as well as characteristic motions. A crude predictor of plasmapause L value (Lpp) in the post-midnight period as a function of magnetic disturbance is the formula Lpp = 5.7-0.47Kp, where Kp is the maximum 3-hour Kp value in the preceding 12 hours. A ground station at L ∼ 3.7 is recommended as optimum for observation of plasmapause-associated effects directly overhead. The plasmasphere is regularly perturbed by substorm-associated convection electric fields, and these apparently have important effects on the nightside ionosphere at middle latitudes. Other known departures of the plasmasphere from corotation are expected to have their counterparts in the ionosphere.

305 citations

Journal ArticleDOI
TL;DR: In this paper, the authors reported regions of enhanced cold plasma, isolated from the main plasmasphere along the Explorer 45 orbit on the equatorial plane, using the sheath induced potentials seen by the electric field experiment.
Abstract: Regions of enhanced cold plasma, isolated from the main plasmasphere along the Explorer 45 orbit on the equatorial plane, are reported using the sheath induced potentials seen by the electric field experiment. The occurrence of these regions has a strong correlation with negative enhancements of Dst, and their locations are primarily in the noon-dusk quadrant. The data support the concept that changes in large scale convection play a dominant role in the formation of these regions. Plasmatails that are predicted from enhancements of large scale convection electric fields in general define where these regions may be found. More localized processes are necessary to account for the exact configuration and structure seen in these regions and may eventually result in detachment from the main plasmasphere.

295 citations

References
More filters
Journal ArticleDOI
TL;DR: The position of the knee in the density of magnetospheric ionization was measured on a high time-resolution basis using whistlers recorded during July and part of August 1963 as discussed by the authors.
Abstract: The position of the knee in the density of magnetospheric ionization was measured on a high time-resolution basis using whistlers recorded during July and part of August 1963. (The knee is an abrupt decrease in magnetospheric ionization density, frequently observed at field lines with an equatorial radius of about 4 RE.) The data were obtained at Eights (64°S dipole latitude) and Byrd (70°S dipole latitude) in the Antarctic. The whistler results and results from other experiments confirm that the knee is a regular feature of the magnetosphere. For conditions of steady, moderate geomagnetic agitation (Kp = 2–4), the diurnal variation in geocentric equatorial range to the knee is remarkably repeatable. It is characterized by (1) a slow inward movement of the knee on the nightside, covering about 1.5 RE in 10 hours; (2) a slight outward movement on the dayside covering about 0.5 RE and (3) a rapid outward shift in the late afternoon covering about 1 RE in 1 hour. During periods of changing magnetic activity, the knee position changes with at most a few hours' delay, moving inward with increasing magnetic activity. The results from Eights and Byrd may be generalized to describe a three-dimensional model of thermal ionization in the magnetosphere involving a dense (∼100 el/cm3) inner region and a tenuous (∼1 el/cm3) outer region separated by a sharp field-aligned boundary, the plasmapause. During the postmidnight hours, the inward motion of the knee involves a corresponding inward motion of the ionization just inside the plasmapause. The rapid outward shift of the knee near 1800 LT does not involve an outward plasma motion, but instead involves the presence of a region of ‘new’ high-density (∼100 el/cm3) plasma in the equatorial range of about 4–5 RE. Preliminary evidence shows that, at least in the period 0000–1700 LT, the ionization inside the plasmapause rotates at approximately the angular velocity of the earth.

557 citations

Journal ArticleDOI
TL;DR: In this article, the magnetic lines of force in the magnetosphere are separated into two groups: those that travel across the tail during the convective motion and those that are never transported to the tail.
Abstract: Magnetospheric convective system proposed by Axford and Hines is revised and made compatible with the view, based on the recently obtained geomagnetic data, that (1) the convective motion induced by the solar wind would penetrate to the innermost part of the magnetosphere, if it were not for the superposed effect of the earth's rotation, and the fact that (2) the earth's magnetosphere has an essentially open tail. Magnetic lines of force in the magnetosphere are then found separated into two groups: those that travel across the tail during the convective motion and those that are never transported to the tail. On field lines of the former group, the plasma density would be less than the value expected on the basis of the equilibrium theory, since the plasma along these field lines can escape to the outer space while the field line travels across the open magnetospheric tail and since the rate of plasma replenishment from lower levels is low. On field lines of the latter group, plasma escape is always prevented by closed field lines, so that the diffusive equilibrium would prevail. Hence at the boundary between these two groups of field lines, the plasma density is expected to show discontinuity. This boundary surface is suggested to be the plasmapause, and various observed features of the plasmapause are explained.

476 citations

Journal ArticleDOI
TL;DR: Polar wind, describing upward plasma expansion of topside polar ionosphere and acceleration of positive H and He ions as discussed by the authors, describes upward plasmas expansion of top-side polar ionosphere.
Abstract: Polar wind, describing upward plasma expansion of topside polar ionosphere and acceleration of positive H and He ions

377 citations

Journal ArticleDOI
TL;DR: In this paper, a new whistler phenomenon called knee whistler is compared with ordinary whistlers and is illustrated by a number of examples recorded at middle and high-latitude stations.
Abstract: Study of a new whistler phenomenon shows that the magnetospheric ionization profile often exhibits a ‘knee,’ that is, a region at several earth radii in which the ionization density drops rapidly from a relatively normal level to a substantially depressed one. The new whistler phenomenon (called, for convenience, the ‘knee whistler’) is compared with ordinary whistlers and is illustrated by a number of examples recorded at middle- and high-latitude stations. It is suggested that the knee exists at all times in the magnetosphere, and that its position varies, moving inward with increasing magnetic activity. There are indications that conditions of whistler-mode propagation may be unusually favorable on the low-latitude side of the knee and that the region on the high-latitude side may be favorable for the production of triggered ionospheric noise. It is pointed out that knee whistlers account for a substantial number of the observations of deep density depressions during magnetic storms. Several questions of interpretation are raised, and the direction of future investigations is indicated.

364 citations

Journal ArticleDOI
TL;DR: In this article, an upper atmosphere geophysical measurements are surveyed to determine to what extent the available data support the concept of bulk motion of the magnetosphere (convection) and the associated electric field.
Abstract: Fast magnetic field-line merging at the magnetospheric bow and in the tail are examined to determine their implications in regard to the concept of bulk motion of the magnetosphere (convection) and the associated electric field. Upper atmosphere geophysical measurements are surveyed to determine to what extent the available data support this concept. The dawn-dusk asymmetry in energetic particle fluxes, the movement of auroral ionization, ionospheric currents, and the location of the whistler knee (or ‘plasmapause’) are all consistent with this concept, the latter three all giving estimates of the electrostatic potential difference across the magnetosphere in the dawn-dusk meridian of a few tens of kilovolts. A ‘present best estimate’ of the flow pattern in the magnetosphere is derived, based primarily on the diurnal variation in the location of the whistler knee. The convective flow in from the tail appears to be stronger before midnight than after, which is consistent with the location of the maximum nighttime precipitation of energetic electrons. The derived flow is also qualitatively in agreement with that deduced from field-line merging. However, the Axford-Hines types of viscous drag will also give rise to convective flow, and the currently available data do not allow a definitive determination of whether field-line merging or viscous interaction is the principal driving force.

338 citations