Abstract
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.
Highlights
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One mechanism is the frictional heating of ions as they convect through the neutral gas, in presence of a DC electric field
Anisotropic ion temperatures were observed in the high-latitude F-region, using the tri-static European Incoherent Scatter (EISCAT) UHF system, during strong convection electric field events (e.g. Perraut et al, 1984; Løvhaug and Fla, 1986)
Summary
The electrostatic dispersion relationship for waves in a drifting collisional bi-Maxwellian plasma with sheared parallel ion flow and finite Lamor radius corrections, can be expressed as. Realistic electron velocity shears were seen to have a small effect on the zero shear solutions (Perron, 2004) The full derivation of Eq (1), which is a generalisation of St-Maurice et al (2007) dispersion relation that includes ion temperature anisotropy, will be presented in a following paper. In this communication, we limit our study to the limiting case where νi,e → 0, or equivalently Ui,e → 0, and for small Larmor radius corrections It is worth noting that for Vdi → 0, the linear dispersion relation for electrostatic waves in anisotropic magnetised hot plasmas is recovered (e.g. Stix, 1992, chap. 11)
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