Electrostatic oscillations due to filamentary structures in the magnetic‐field‐aligned flow: The ion‐acoustic branch

Gavrishchaka, Valeriy V.; Ganguli, Supriya B.; Ganguli, G.

doi:10.1029/1999ja900094

Cited by 66 publications

(58 citation statements)

References 71 publications

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“…On the basis of theoretical studies about current instabilities in the magnetosphere for a homogenous plasma (Kindel and Kennel, 1971), current thresholds are too high, and these mechanisms may not operate over a broad altitude range. For an inhomogenous plasma, if sheared flows are present, as it is likely in the auroral region, the thresholds are significantly lower (Gavrishchaka et al, 1999(Gavrishchaka et al, , 2000. In these latter works, the instability mechanism has been described in a local limit and has been successfully applied only to observations in the nightside upward current region by FAST at an altitude of 4 000 km.…”

Section: Discussionmentioning

confidence: 99%

Modeling transverse heating and outflow of ionospheric ions from the dayside cusp/cleft. 2 Applications

et al. 2003

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Abstract. In this paper, we consider major ion energization mechanisms in the dayside cusp/cleft region. This includes transverse ion heating by ion cyclotron resonance (ICR), ion energization through structures of field-aligned electric potential drops, and transverse heating by lower hybrid (LH) waves. First, we present and discuss three typical cusp/cleft crossings associated with one of the first two mechanisms mentioned above. Then, we develop a procedure for finding the altitude dependence of ICR heating for any data set in the high-altitude cusp/cleft under the absence of field-aligned potential drops. This has been accomplished using a large set of numerical simulations from a two-dimensional, steadystate, Monte Carlo, trajectory-based code, as discussed in detail in the first companion paper (Bouhram et al., 2003).The procedure is applied and tested successfully for the first two events, by using patterns of ion moments along the satellite track as constraints. Then, we present a statistical study that uses 25 cusp/cleft crossings associated with steady IMF conditions, where ICR heating is expected to occur alone. It is pointed out that the ICR heating increases gradually versus geocentric distance as s 3.3±1.8 . The inferred values of the wave power and the spectral index associated with the component responsible for ICR heating are lower than those characterizing the broad-band, extremely low-frequency (BBELF) turbulence usually observed in the cusp/cleft. This strengthens the idea that more than one wave-mode is contained in the BBELF turbulence, and only a small fraction of the observed turbulence is responsible for ICR heating. Then, we study the occurrence versus magnetic local time (MLT) of field-aligned potential drops. According to previous statistical studies, such structures are not common in the cusp and tend to be associated with the cleft region. We also discuss the effects of LH heating in the cusp on the observed ion distributions. However, this mechanism turns out to be of less importance than ICR heating.

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Section: Discussionmentioning

confidence: 99%

Modeling transverse heating and outflow of ionospheric ions from the dayside cusp/cleft. 2 Applications

et al. 2003

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“…This may explain why emissions with k || >k ⊥ occur only in short bursts, and why waves with k || <k ⊥ may exist in longer bursts and are more common. We note that in an inhomogeneous plasma, including, for example, a varying particle drift along the geomagnetic field, IA waves may also exist for other temperature ratios (Ganguli et al, 2002 andGavrishchaka et al, 1999). Different directions of the k-vector correspond to different wave modes, assigned different names, but there is no sharp theoretical limit between the different modes.…”

Section: Discussionmentioning

confidence: 99%

Identification of broad-band waves above the auroral acceleration region: Cluster observations

et al. 2004

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Abstract. We investigate broad-band emissions at frequencies above the ion gyrofrequency on auroral field lines at geocentric distances of about 4.5 Earth radii. Observations by the Cluster satellites are used to study the wave characteristics and to determine the wave modes involved. All events include some bursts of broad-band emissions with a substantial component of the electric field parallel to the geomagnetic field. Studying the polarization of the emissions we find that linear waves in a homogeneous plasma can be used to theoretically describe the observations. The broad-band emissions include short bursts of ion acoustic waves, and longer periods of ion Bernstein and Electrostatic Ion Cyclotron (EIC) waves. All waves occur during the same event within a few seconds, with EIC waves as the most common. Theoretically, there is no sharp limit between these wave modes and they can be described by the same dispersion surface. These emissions are closely associated with low-frequency Alfvén waves, indicating a possible generation mechanism.

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“…The role of transverse shears in FA ion drifts on electrostatic IA instability eigenmodes and threshold conditions was studied by Gavrishchaka et al (1998) and Gavrishchaka et al (1999). In particular, they suggested that velocity shears can significantly lower the threshold current of the current-driven electrostatic ion-acoustic (CDEIA) instability, even when T i ∼ T e .…”

Section: Introductionmentioning

confidence: 99%

“…Later, Perron et al (2009) systematically studied the threshold solutions of St-Maurice et al (2007) kinetic dispersion relation for different ion to electron temperature ratios. Besides, the Gavrishchaka et al (1998) and Gavrishchaka et al (1999) work was extended by Spangler et al (2002) who derived a dispersion relation for a Maxwellian plasma which includes temperature anisotropy and shears. They showed that ion temperature anisotropy alters the frequency modes of the sheared CDEIA instability by solving numerically the dispersion equation.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2013

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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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Electrostatic oscillations due to filamentary structures in the magnetic‐field‐aligned flow: The ion‐acoustic branch

Cited by 66 publications

References 71 publications

Modeling transverse heating and outflow of ionospheric ions from the dayside cusp/cleft. 2 Applications

Modeling transverse heating and outflow of ionospheric ions from the dayside cusp/cleft. 2 Applications

Identification of broad-band waves above the auroral acceleration region: Cluster observations

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

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