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Satellite (IC-B-1300) data on the electromagnetic structures in the high-latitude ionosphere are presented. One can observe three kinds of vortices, namely vortex chains as well as solitary dipolar and monopolar vortex structures. The theoretical treatment that is carried out in the present paper is in reasonable agreement with the observations.

Abstract. A linear theory of mirror instability accounting for the finite electron temperature effects is developed. Using the standard low-frequency approach to the analysis of this instability but including some kinetic effects, we have derived an expression for the growth rate and analyzed the effects of finite electron temperature and arbitrary electron anisotropy. In comparison with earlier analyses which were limited to isotropic electron distributions, consideration of arbitrary electron anisotropy shows that for sufficiently hot electrons an increased electron temperature enhances the growth rate of the mirror instability. IntroductionThe The incorporation of finite electron temperature effects, and more generally the inclusion of arbitrary electron anisotropy is the main goal of the present paper. Thus the results can be applied not only to the mirror waves observed in the magnetosheath but also to those observed in other regions of space plasma (e.g., the ring current).The second goal of the present paper is to correct previously obtained results in the limit of an isotropic electron distribution. This correction is required because of the importance of resonance terms in the equation governing the motion of electrons in the direction parallel to the magnetic field. These terms have been overlooked in some previous studies. This resulted in an incorrect expression for the growth rate of the mirror instability in a plasma with finite electron temperature.The paper is organized in the following fashion: In section 2 we derive the hydrodynamic equations necessary for the study of mirror instability. The expression for the growth rate of the mirror mode in an 2393

[1] A fully kinetic theory of the magnetic mirror instability in high-b space plasmas accounting for arbitrary ion-Larmor radius effects is developed. It is shown that incorporation of ion-Larmor radius effects leads to a substantial modification of both the instability growth rate and the instability threshold. For wavelengths of the order of the ion-Larmor radius the effective elasticity of the magnetic field lines is substantially enhanced, yielding an increase in the instability threshold. We derive a compact expression for the growth rate of the fastest-growing mode in the fully kinetic limit. Furthermore, it is shown that in the presence of finite ion-Larmor radius effects a noncoplanar component of the magnetic field perturbations appears. Such a component is usually present in satellite measurements of mirror modes. The relevance of these results in understanding observations of mirror instability-generated signals in space plasmas is outlined.

[1] A theory of finite-amplitude mirror type waves in non-Maxwellian space plasmas is developed. The collisionless kinetic theory in a guiding center approximation, modified for accounting of the finite ion Larmor radius effects, is used as the starting point. The model equation governing the nonlinear dynamics of mirror waves near instability threshold is derived. In the linear approximation it describes the classical mirror instability that is valid for a wide class of the velocity distribution functions. In the nonlinear regime the mirror waves form solitary structures that have the shape of magnetic holes. The formation of such structures and their nonlinear dynamics has been analyzed both analytically and numerically. It is suggested that the main nonlinear mechanism responsible for mirror instability saturation is associated with modification (flattening) of the shape of the background ion distribution function in the region of small parallel particle velocities. The width of this region is of the order of the particle trapping zone in the mirror hole. Near the mirror instability threshold the saturation arises before its width reaches the ion thermal velocity. The nonlinear mode coupling effects in this approximation are smaller and unable to take control over evolution of the space profile of saturated mirror waves or lead to their magnetic collapse. This results in the appearance of quasi-stable solitary mirror structures having the form of deep magnetic depressions. A phenomenological description of this process is formulated. The relevance of the theoretical results to recent satellite observations is stressed.