Characteristics of low‐energy plasma in the plasmasphere and plasma trough

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Low‐energy (<100 eV) ion data from the plasma composition experiment on ISEE 1 are examined statistically to study pitch angle distributions in all local times of the magnetosphere (L = 3–10). The pitch angle distributions in the data set used here can be classified into seven types; however, there are four major types, i.e., isotropic distribution, bi‐directional field‐aligned distribution, unidirectional field‐aligned distribution, and low flux. The isotropic distribution that consists of very low energy (typically <10 eV) ions is a persistent feature in the inner region. It is frequently observed with an accompanying loss cone‐like structure. The bi‐directional field‐aligned distribution consisting of warm ions (⩾10 eV) is a persistent feature on the outer dayside and it is seen just outside the isotropic distribution region of the nightside. It is noted that the loss cone‐like structure is also a common feature of this type of distribution in the noon sector. On the outer nightside the unidirectional field‐aligned distribution consisting of warm ions is the dominant signature, but in some cases only the low flux (no appreciable flux) is observed. The ‘sources’ of ions in various regions are discussed on the basis of these results and others.

Section: Relationship Of Low-energy (• 100 Ev)mentioning

confidence: 57%

Low‐energy (<100 eV) ion pitch angle distributions in the magnetosphere by ISEE 1

Nagai¹,

Johnson²,

Chappell³

1983

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“…The possibility that the erosion process may be turbulent in nature has been suggested by Reasoner et al [1983] During some periods, such as the ones illustrated in this paper, a bulge effect may be observed in whistler data on only a fraction of the days, say less than 20%, and the statistics on plasmasphere radius at dusk may not differ substantially from those for the dawn sector. In the quiet sun years 1963 and 1965, a well defined bulge was observed on a large fraction of the observing days, being particularly common in multiday periods of relatively steady substorm activity following weak magnetic storms.…”

Section: 266mentioning

confidence: 64%

“…Their loss of plasma occurs at a time when the underlying ionosphere is found to be depleted, supposedly by the perturbing effects of electric fields and associated Joule heating [e.g., Aarons and Rodger, 1991]. In the aftermath of an increase in disturbance levels, warm light ions (,--,5 eV) can be observed in bulge regions close to the main plasmasphere (see also Reasoner et al [1983]). 12.…”

Section: Discussionmentioning

confidence: 99%

Plasmasphere dynamics in the duskside bulge region: A new look at an old topic

Carpenter¹,

Giles²,

Chappell³

et al. 1993

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132

101

Data acquired during several multiday periods in 1982 at ground stations Siple, Halley, and Kerguelen and on satellites DE 1, ISEE 1, and GEOS 2 have been used to investigate thermal plasma structure and dynamics in the duskside plasmasphere bulge region of the Earth. The distribution of thermal plasma in the dusk bulge sector is difficult to describe realistically, in part because of the time integral manner in which the thermal plasma distribution depends upon the effects of bulk cross‐B flow and interchange plasma flows along B. While relatively simple MHD models can be useful for qualitatively predicting certain effects of enhanced convection on a quiet plasmasphere, such as an initial sunward entrainment of the outer regions, they are of limited value in predicting the duskside thermal plasma structures that are observed. Furthermore, use of such models can be misleading if one fails to realize that they do not address the question of the formation of the steep plasmapause profile or provide for a possible role of instabilities or other irreversible processes in plasmapause formation. Our specific findings, which are based both upon the present case studies and upon earlier work, include the following: (1) during active periods the plasmasphere appears to become divided into two entities, a main plasmasphere and a duskside bulge region. The latter consists of outlying or outward extending plasmas that are the products of erosion of the main plasmasphere; (2) in the aftermath of an increase in convection activity, the main plasmasphere tends (from a statistical point of view) to become roughly circular in equatorial cross section, with only a slight bulge at dusk; (3) the abrupt westward edge of the duskside bulge observed from whistlers represents a state in the evolution of sunward extending streamers; (4) in the aftermath of a weak magnetic storm, 10 to 30% of the plasma “removed” from the outer plasmasphere appears to remain in the afternoon‐dusk sector beyond the main plasmasphere. This suggests that plasma flow from the afternoon‐dusk magnetosphere into the boundary layers is to some extent impeded, possibly through a mechanism that partially decouples the high altitude and ionospheric‐level flow regimes; (5) outlying dense plasma structures may circulate in the outer duskside magnetosphere for many days following an increase in convection, unless there is extremely deep quieting; (6) a day‐night plasmatrough boundary may be identified in equatorial satellite data; (7) factor‐of‐2‐to‐10 density irregularities appear near the plasmapause in the postdusk sector in the aftermath of weak magnetic storms; (8) during the refilling of the plasmatrough from the ionosphere at L = 4.6, predominantly bidirectional field aligned and equatorially trapped light ion pitch angle distributions give way to a predominantly isotropic distribution (as seen by DE 1) when the plasma density reaches a level a factor of about 3 below the saturated plasmasphere level; (9) some outlying dense plasma structures are effectively det...

“…It was found that the O + component had negligible contribution to the wave growth of EMIC and the thermal (<100 eV) helium He + component had a modest effect on the wave growth of EMIC due to the cyclotron damping [e.g., Xue et al 1996]. Since in the outer magnetosphere (e.g., near the geostationary orbit) the cold ion component have typical energies <10 eV [ Reasoner et al , 1983; Moldwin et al , 1994], without lose of generality, it is reasonable to assume that the space plasma is comprised of isotropic cold ( T c → 0) components with density n σ ( σ = 0, 1, 2 and 3 refer to electrons, H + , He + and O + ), and an anisotropic ( T ⊥ / T ∥ > 1) hot H + population with density n h . We assume that the fractional composition of ion species is given by η 1 = n 1 / n 0 , η h = n h / n 0 , η 2 = n 2 / n 0 , η 3 = n 3 / n 0 , and η 1 + η h + η 2 + η 3 = 1.…”

Section: Emic Instability Threshold Conditionmentioning

confidence: 99%

Electromagnetic ion cyclotron waves instability threshold condition of suprathermal protons by kappa distribution

Xiao

Zhou

et al. 2007

[1] The well-known generalized Lorentzian (kappa) distribution generally provides a good representation for the high-energy tail population of natural cosmic suprathermal plasmas. In this study we examine the electromagnetic ion cyclotron waves (EMIC) instability driven by the temperature anisotropy condition (T ? /T k > 1) of suprathermal protons modeled with a typical kappa distribution in a cold multispecies plasma (electron, H + , He + , and O + ). Since the EMIC wave instability is found to be significant typically above the O + band, we apply a linear theory to study the instability threshold condition for the He + and H + bands particularly around the geostationary orbit. The instability threshold condition, as in the case for a regular bi-Maxwellian, is found to follow a typical form T ? /T k À 1 = S/b k a , with higher values in the He + band than those in the H + band in the case of the strong wave instability owing to a lower maximum wave growth in the He + band. As the spectral index k increases, the instability threshold condition generally decreases and tends to the lowest limiting values of the bi-Maxwellian, since the evaluation by the bi-Maxwellian generally overestimates the maximum wave growth. The densities of the cold components (particularly protons) have impacts on the threshold condition primarily in the H + band, with a higher density of cold protons leading to a lower value of the threshold condition. The results above may further reveal the nature of this instability threshold condition for the EMIC waves in any other space plasmas where an anisotropic suprathermal ion component and cold multicomponents are present together.