Velocity shear and current driven instability in a collisional F-region

Abstract. We have studied how the presence of collisions affects the behavior of instabilities triggered by a combination of shears and parallel currents in the ionosphere under a variety of ion to electron temperature ratios. To this goal we have numerically solved a kinetic dispersion relation, using a relaxation model to describe the effects of ion and electron collisions. We have compared our solutions to expressions derived in a fluid limit which applied only to large electron to ion temperature ratios. We have limited our study to threshold conditions for the current density and the shears. We have studied how the threshold varies as a function of the wave-vector angle direction and as a function of frequency. As expected, we have found that for low frequencies and/or elevated ion to electron temperature ratios, the kinetic dispersion relation has to be used to evaluate the threshold conditions. We have also found that ion velocity shears can significantly lower the field-aligned threshold current needed to trigger the instability, especially for wave-vectors close to the perpendicular to the magnetic field. However the current density and shear requirements remain significantly higher than if collisions are neglected. Therefore, for ionospheric F-region applications, the effect of collisions should be included in the calculation of instabilities associated with horizontal shears in the vertical flow. Furthermore, in many situations of interest the kinetic solutions should be used instead of the fluid limit, in spite of the fact that the latter can be shown to produce qualitatively valid solutions.

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Ion temperature anisotropy effects on the dispersion relation and threshold conditions of a sheared current-driven electrostatic ion-acoustic instability with applications to the collisional high-latitude F-region

Journal of Plasma Physics ◽

10.1017/s0022377814000440 ◽

2014 ◽

Vol 81 (1) ◽

Cited By ~ 1

Author(s):

Patrick J.G. Perron ◽

J.-M. Noël ◽

J.-P. St-Maurice ◽

K. Kabin

Keyword(s):

Dispersion Relation ◽

Wave Vector ◽

High Latitude ◽

Instability Threshold ◽

Larmor Radius ◽

Ion Temperature ◽

Temperature Anisotropy ◽

F Region ◽

Threshold Conditions ◽

Ion Acoustic

Plasma instabilities play a important role in producing small-scale irregularities in the ionosphere. In particular, current-driven electrostatic ion-acoustic (CDEIA) instabilities contribute to high-latitude F-region electrodynamics. Ion temperature anisotropies with enhanced perpendicular temperature often exist in the high-latitude F-region. In addition to temperature anisotropies, ion velocity shears are observed near auroral arc edges, sometimes coexisting with thermal ion upflow processes and field-aligned currents (FAC). We investigated whether ion temperature anisotropy lowers the threshold conditions required for the onset of sheared CDEIA instabilities. We generalised a dispersion relation to include ion thermal anisotropy, finite Larmor radius corrections and collisions. We derived new fluid-like analytical expressions for the threshold conditions required for instability that depend explicitly on ion temperature anisotropy. We studied how the instability threshold conditions vary as a function of the wave vector direction in both fluid and kinetic regimes. We found that, despite the dampening effect of collisions on ion-acoustic waves, ion temperature anisotropy lowers in some cases the threshold drift requirements for a large range of oblique wave vector angles. More importantly, realistic ion temperature anisotropies contribute to reducing the instability threshold velocity shears that are associated with small drift thresholds, for modes propagating almost perpendicularly to the geomagnetic field. Small shear thresholds that seem to be sustainable in the ionospheric F-region are obtained for low-frequency waves. Such instabilities could play a role in the direct generation of field-aligned irregularities in the collisional F-region that could be observed with the Super Dual Auroral Radar Network (SuperDARN) array of high-frequency radars. These modes would be very sensitive to the radar probing direction since they are restricted to very narrow angular intervals. The ion temperature anisotropy is an important parameter that needs to be considered in the studies of sheared and collisional CDEIA waves and instabilities in the high-latitude F-region.

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Ionospheric heating in the F -region

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1964.0174 ◽

1964 ◽

Vol 281 (1384) ◽

pp. 140-149 ◽

Cited By ~ 17

Keyword(s):

Electron Temperature ◽

Energy Input ◽

Particle Flux ◽

Electron Interaction ◽

Ion Temperature ◽

Ionospheric Heating ◽

F Region ◽

Field Lines ◽

Photo Ionization ◽

Made In

Measurements of electron temperature made in Ariel I have been analyzed to calculate the ionospheric energy input required to maintain the electron temperature above the ion temperature. The results are found to be consistent with the energy input due to photo-ionization in the daytime, provided that allowance is made for the effects of the escaping flux of photoelectrons spiralling upwards along the geomagnetic field lines which impartenergy to the ionosphere by electron-electron interaction. However, it is found that during the night an energy input of particle origin is observed, a close agreement being found between the distribution of energy input and that of the fluxes of low-energy particles observed by Savenko, Shavrin & Pisavenko 1963. The particle flux contributes less than 30% to the heat input in the daytime and its diurnal variation is small.

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The frequency and damping of ion-acoustic waves

Canadian Journal of Physics ◽

10.1139/p80-080 ◽

1980 ◽

Vol 58 (4) ◽

pp. 565-568 ◽

Cited By ~ 2

Author(s):

A. J. Barnard ◽

C. Gulizia

Keyword(s):

Dispersion Relation ◽

Electron Temperature ◽

Acoustic Waves ◽

Ion Temperature ◽

Ion Acoustic Waves ◽

Ion Acoustic

The dispersion relation for a plasma with different ion and electron temperatures is solved numerically to obtain the frequency and the damping constant for ion-acoustic waves as a function of the wavenumber. It is shown that the commonly used expressions for these variables only apply if the parameter T = ziTe/Ti is larger than 20, and can lead to large errors if T is close to 1. (Here z1 is the ion charge, Te is the electron temperature, and Ti the ion temperature.) Tables and graphs of the frequency and damping as functions of the wavenumber are given for different values of T.

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On the usefulness of <i>E</i> region electron temperatures and lower <i>F</i> region ion temperatures for the extraction of thermospheric parameters: a case study

Annales Geophysicae ◽

10.1007/s00585-999-1182-2 ◽

1999 ◽

Vol 17 (9) ◽

pp. 1182-1198 ◽

Cited By ~ 9

Author(s):

J.-P. St.-Maurice ◽

C. Cussenot ◽

W. Kofman

Keyword(s):

Electric Field ◽

Electron Temperature ◽

Plasma Temperature ◽

Ion Temperature ◽

Heating Rates ◽

Neutral Winds ◽

F Region ◽

E Region ◽

Effective Electric Field ◽

Temperature Observations

Abstract. Using EISCAT data, we have studied the behavior of the E region electron temperature and of the lower F region ion temperature during a period that was particularly active geomagnetically. We have found that the E region electron temperatures responded quite predictably to the effective electric field. For this reason, the E region electron temperature correlated well with the lower F region ion temperature. However, there were several instances during the period under study when the magnitude of the E region electron temperature response was much larger than expected from the ion temperature observations at higher altitudes. We discovered that these instances were related to very strong neutral winds in the 110-175 km altitude region. In one instance that was scrutinized in detail using E region ion drift measurement in conjunction with the temperature observations, we uncovered that, as suspected, the wind was moving in a direction closely matching that of the ions, strongly suggesting that ion drag was at work. In this particular instance the wind reached a magnitude of the order of 350 m/s at 115 km and of at least 750 m/s at 160 km altitude. Curiously enough, there was no indication of strong upper F region neutral winds at the time; this might have been because the event was uncovered around noon, at a time when, in the F region, the E×B drift was strongly westward but the pressure gradients strongly northward in the F region. Our study indicates that both the lower F region ion temperatures and the E region electron temperatures can be used to extract useful geophysical parameters such as the neutral density (through a determination of ion-neutral collision frequencies) and Joule heating rates (through the direct connection that we have confirmed exists between temperatures and the effective electric field).Key words. Ionosphere (auroral ionosphere; ionosphere atmosphere interactions; plasma temperature and density)

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Gyrokinetic stability of electron–positron–ion plasmas

Journal of Plasma Physics ◽

10.1017/s0022377818000181 ◽

2018 ◽

Vol 84 (1) ◽

Cited By ~ 7

Author(s):

A. Mishchenko ◽

A. Zocco ◽

P. Helander ◽

A. Könies

Keyword(s):

Dispersion Relation ◽

Temperature Gradient ◽

Electron Temperature ◽

Alfven Wave ◽

Ion Temperature ◽

Slab Geometry ◽

Ion Temperature Gradient ◽

Electron Temperature Gradient ◽

Electron Positron ◽

Ion Proton

The gyrokinetic stability of electron–positron plasmas contaminated by an ion (proton) admixture is studied in a slab geometry. The appropriate dispersion relation is derived and solved. Stable K-modes, the universal instability, the ion-temperature-gradient-driven instability, the electron-temperature-gradient-driven instability and the shear Alfvén wave are considered. It is found that the contaminated plasma remains stable if the contamination degree is below some threshold and that the shear Alfvén wave can be present in a contaminated plasma in cases where it is absent without ion contamination.

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Ion temperature anisotropy effects on threshold conditions of a shear-modified current driven electrostatic ion-acoustic instability in the topside auroral ionosphere

Annales Geophysicae ◽

10.5194/angeo-31-451-2013 ◽

2013 ◽

Vol 31 (3) ◽

pp. 451-457 ◽

Cited By ~ 1

Author(s):

P. J. G. Perron ◽

J.-M. A. Noël ◽

K. Kabin ◽

J.-P. St-Maurice

Keyword(s):

Acoustic Waves ◽

Larmor Radius ◽

Ion Temperature ◽

Temperature Anisotropy ◽

Finite Larmor Radius ◽

Acoustic Instability ◽

Preferred Direction ◽

F Region ◽

Threshold Conditions ◽

Ion Acoustic

Abstract. Temperature anisotropies may be encountered in space plasmas when there is a preferred direction, for instance, a strong magnetic or electric field. In this paper, we study how ion temperature anisotropy can affect the threshold conditions of a shear-modified current driven electrostatic ion-acoustic (CDEIA) instability. In particular, this communication focuses on instabilities in the context of topside auroral F-region situations and in the limit where finite Larmor radius corrections are small. We derived a new fluid-like expression for the critical drift which depends explicitly on ion anisotropy. More importantly, for ion to electron temperature ratios typical of F-region, solutions of the kinetic dispersion relation show that ion temperature anisotropy may significantly lower the drift threshold required for instability. In some cases, a perpendicular to parallel ion temperature ratio of 2 and may reduce the relative drift required for the onset of instability by a factor of approximately 30, assuming the ion-acoustic speed of the medium remains constant. Therefore, the ion temperature anisotropy should be considered in future studies of ion-acoustic waves and instabilities in the high-latitude ionospheric F-region.

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