Thermal convection for a Darcy-Brinkman rotating anisotropic porous layer in local thermal non-equilibrium

The onset of natural convection in a fluid-saturated anisotropic porous layer, which rotates about the vertical axis, under the hypothesis of local thermal non-equilibrium, is analysed. Since the porosity of the medium is assumed to be high, the more suitable Darcy-Brinkman model is adopted. Linear instability analysis of the conduction solution is carried out. Nonlinear stability with respect to $$L^2$$ L 2 -norm is performed in order to prove the coincidence between the linear instability and the global nonlinear stability thresholds. The effect of both rotation and thermal and mechanical anisotropies on the critical Rayleigh number for the onset of instability is discussed.

Mirror instability driven by pickup ions in the outer heliosheath

<p><span class="fontstyle0">Kinetic linear instability analysis and hybrid simulations are carried out to examine the role of mirror instability in scattering the pickup ions in the outer heliosheath. The dynamics of these pickup ions is essential to<br />the understanding of the energetic neutral atom (ENA) ribbon observed by the Interstellar Boundary EXplorer<br />(IBEX). While most previous studies have focused on the ion cyclotron instability driven by the pickup ions,<br />recent work based on a simple ring velocity distribution of the pickup ions suggested that the mirror mode can<br />also be unstable and contribute to the scattering of the pickup ions. The present study performs linear analysis<br />as well as hybrid simulations for a more realistic, multi-component pickup ion velocity distribution given by the<br />global modeling of neutral atoms in the heliosphere. The linear theory results indicate unstable mirror modes<br />with considerable growth rates. The corresponding hybrid simulations further confirm that the mirror modes can<br />grow and aid the pitch-angle broadening of the pickup ions. So the role of mirror mode should not be ignored in<br />the stability study of the outer heliosheath pickup ions.</span> </p>