Thermal expansion of atmosphere and stability of vertically stratified fluids

The influence of the thermal expansion of the Earth's atmosphere on the stability of vertical stratification of fluid density and temperature is studied. We show that such an influence leads to the instability of incompressible flows. Modified by the thermal expansion coefficient, a new expression for the Brunt-V{\"a}is{\"a}l{\"a} frequency is derived, and a critical value of the thermal expansion coefficient for which the instability occurs is revealed.Comment: 6 pages, 3 figures; Revised version to appear in Physics Letters A (2023

Destabilization of fast magnetoacoustic waves by circulating energetic ions in toroidal plasmas

An instability of fast magnetoacoustic waves (FMW) driven by circulating energetic ions in axisymmetric toroidal plasmas and characterized by the frequencies below the ion gyrofrequency is considered. An important role of the l=0 resonance (l is the number of a cyclotron harmonic) in the wave-particle interaction is revealed: It is shown that this resonance considerably extends an unstable region in the space of the pitch-angles of the energetic ions and the wave frequencies. The analysis is carried out for a ''slow'' instability, which has the growth rate less than the bounce frequency of the energetic ions. Specific examples relevant to the National Spherical Torus Experiment (NSTX) [J. Spitzer et al., Fusion Technol. 30 (1996) 1337], where instabilities of this kind were observed, are considered

Bi-directional Alfv\'en Cyclotron Instabilities in the Mega-Amp Spherical Tokamak

Alfv\'en cyclotron instabilities excited by velocity gradients of energetic beam ions were investigated in MAST experiments with super-Alfv\'enic NBI over a wide range of toroidal magnetic fields from ~0.34 T to ~0.585 T. In MAST discharges with high magnetic field, a discrete spectrum of modes in the sub-cyclotron frequency range is excited toroidally propagating counter to the beam and plasma current (toroidal mode numbers n < 0).Comment: 28 pages, 13 figures. This article has been submitted to Physics of Plasmas. After it is published, it will be found at http://scitation.aip.org/content/aip/journal/pop/brows

Nonlinear dynamics of the electromagnetic ion cyclotron structures in the inner magnetosphere

[1] Electromagnetic ion cyclotron waves, called EMICs, are widely observed in the inner magnetosphere and can be excited through various plasma mechanisms such as ion temperature anisotropy. These waves interact with magnetospheric particles, which they can scatter into the loss cone. This paper investigates how nonlinearities in the ion fluid equations governing the electromagnetic ion cyclotron waves cause large-amplitude EMIC waves to evolve into coherent nonlinear structures. Both planar soliton structures and also two-dimensional vortex-like nonlinear structures are found to develop out of these nonlinearities

Shear flow-driven magnetized Rossby wave dynamics in the Earth's ionosphere

Taking into account the action of inhomogeneous zonal wind (shear flow), nonlinear dynamic equations describing the propagation of planetary ULF magnetized Rossby waves in the ionospheric D-, E-, and F-layers are obtained and investigated. The influence of existence of charged particles through Hall and Pedersen conductivities on such dynamic equations is studied in detail. It is shown that the existence of shear flow and Pedersen conductivity can be considered as the presence of an external energy source. The possibility of a barotropic instability of the magnetized Rossby waves is shown. Based on the Rayleigh's theorem, the appropriate stability conditions are defined in case of the ionospheric D- and E-layers. It is indicated that magnetized Rossby waves under the action of shear zonal flow correspond to states with negative energy. Some exponentially localized vortical solutions are found for the ionospheric D- and E-layers.Joint Call of Shota Rustaveli National Science Foundation of Georgia [04/01]; Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK)The carried out investigation is supported through the Grant No. 04/01 of 2017 Joint Call of Shota Rustaveli National Science Foundation of Georgia and the Scientific and Technological Research Council of Turkey (TUBITAK)