Abstract. It is becoming increasingly clear that electron thermal e ects have to be taken into account when dealing with the theory of ionospheric instabilities in the high-latitude ionosphere. Unfortunately, the mathematical complexity often hides the physical processes at work. We follow the limiting cases of a complex but systematic generalized¯uid approach to get to the heart of the thermal processes that a ect the stability of E region waves during electron heating events. We try to show as simply as possible under what conditions thermal e ects contribute to the destabilization of strongly ®eld-aligned (zero aspect angle) Farley-Buneman modes. We show that destabilization can arise from a combination of (1) a reduction in pressure gradients associated with temperature¯uctuations that are out of phase with density¯uctuations, and (2) thermal di usion, which takes the electrons from regions of enhanced temperatures to regions of negative temperature¯uctu-ations, and therefore enhanced densities. However, we also show that, contrary to what has been suggested in the past, for modes excited along the E 0 Â B direction thermal feedback decreases the growth rate and raises the threshold speed of the Farley-Buneman instability. The increase in threshold speed appears to be important enough to explain the generation of`Type IV' waves in the high-latitude ionosphere.

In this paper we develop the complete theory of the relativistic motion of a singular layer of matter under the influence of surface tension and volume tension. In order to account for vacuum tension effects we suggest a formalism of universal applicability: the single degree of freedom of a relativistic "bubble" is coupled in a gauge-invariant manner to a potential three-form A in the presence o f gravity. The mathematical and physical consequences of this coupling can be summarized as follows. (i) The action functional of the theory, when written in geometric form, is formally quite similar to the Einstein-Maxwell action for the dynamics of a point charge on a Riemannian manifold. However, in comparison with electrodynamics, bubble dynamics is a highly constrained theory with a vastly different physical content: the gauge field F = d A propagates no degrees of freedom and when it is coupled to gravity alone, it gives rise to a cosmological constant of arbitrary magnitude. (ii) We exploit this peculiar property of the gauge field to solve exactly some of the equations of motion of bubble dynamics. The net physical result is the nucleation of bubbles in different "vacuum phases" of the de Sitter type characterized by two effective and distinct cosmological constants, one inside and one outside the domain wall. (iii) Because of the generality of the above mechanism, the theory is applicable to a variety of different physical situations; in the case of a spherical bubble we derive the radial equation of motion and solve it explicitly in a number of cases of physical interest ranging from cosmology to particle physics. Thus, in curved spacetime we find that our action functional provides a natural basis for the so-called inflationary cosmology; in flat spacetime we find that our action functional generates the same vacuum tension advocated in the so-called "bag model" of strong interactions in order to confine quarks and gluons.

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Based on the linear dispersion relation of Kissack et al., Phys. Plasmas 15, 022901 (2008), the physical processes that define altitude behavior of marginally stable Farley–Buneman waves in the equatorial electrojet are investigated. The expressions derived for the angular frequency and growth rate are presented in such a way as to make it easy to track the dominant physical processes and to see the relation with earlier work. Two dimensionless parameters are identified that are helpful in showing the transition between altitude and wavelength domains where different thermal processes dominate. The difference in phase velocity between vertical and off-vertical transmissions (zero versus nonzero flow angles) is found to be due to Dimant–Sudan effects, which are preferentially less important at higher altitudes and shorter wavelengths.

The traditional linear fluid dispersion relation of Farley–Buneman waves has been generalized by including, for the electron gas, the effects of collisional energy exchange, as well as thermal force and thermoelectric effects associated with heat flow. The formalism used is that of Schunk [Rev. Geophys. Space Phys. 15, 429 (1977)] for Grad’s 8-moment approximation, to which inelastic energy exchange has been added phenomenologically. The resulting dispersion relation recovers both the traditional isothermal and adiabatic limits, as well as the dispersion relation of Pécseli et al. [J. Geophys. Res. 94, 5337 (1989)] as a special case. Owing to the fact that the electron–neutral interaction is far from being of the Maxwell molecule type, it is found that, contrary to suggestions in the literature, adiabaticity does not hold at the larger wavelengths of the instability. In the small wave-number limit, the linear instability threshold speed of the waves takes the form [(γeTe0+Ti0)/mi]1/2, with the effective γe being a sensitive function of aspect angle. Its value can be as small as 0.28 or as large as 3.4 depending on conditions.