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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.

Abstract. A new model of the ionospheric Alfv•n resonator (IAR) including the effect of wave frequency dispersion is presented. It is shown that the shear Alfv•n waves in the IAR are coupled to the compressional mode through the boundary conditions at the ionosphere. This coupling results in the appearance of the Hall dispersion and subsequent shift of the IAR frequency spectrum. The excitation mechanism involving the IAR interaction with the magnetospheric convective flow is considered. It is shown that the Hall dispersion of the IAR eigenmode increases the growth rate of the feedback instability. However, for the observed values of ionospheric conductivity this effect is not very high. It is shown that the physical mechanism of the feedback instability is similar to the Cerenkov radiation in collisionless plasmas. The IAR eigenfrequencies and growth rates are evaluated for the case of exponential variation of the Alfv•n velocity with altitude in the topside ionosphere. In this paper we will generalize the previous analysis by incorporating the dispersion of shear Alfvdn waves in the ionosphere-magnetosphere coupled system. We will show that this dispersion is produced by the ionospheric Hall current which arises due to the coupling of shear Alfvdn and fast magnetosonic (compressional) waves in the ionosphere. The deceleration of the Alfvdn phase velocity due to the Hall dispersion may increase the rate of energy transfer from the convective flow to IAR eigenmodes and overcome the dissipation rate due to the leakage of energy through the IAR upper boundary. The physical mechanism of such an instability, which we will term below as "feedback instability", is similar to the usual (•erenkov radiation in collisionless plasma.The paper is organized as follows: Section 2 describes the boundary conditions of the resonant cavity at the ionospheric and magnetospheric ends. The analysis of the dispersive ionospheric Alfvdn resonator is given in section 3. The dispersion relation for the feedback instability is presented in section 4. Excitation of dispersive eigenoscillations by the feedback instability in the lowconductivity ionosphere is considered in section 5. The case for a highly conductive ionosphere is analyzed in section 6. Our discussions and conclusions are found in section 7. 7737

[1] A unified theory of the mirror instability in space plasmas is developed. In the standard quasi-hydrodynamic approach, the most general mirror-mode dispersion relation is derived and the growth rate of the mirror instability is obtained in terms of arbitrary electron and ion velocity distribution functions. Finite electron temperature effects and arbitrary electron temperature anisotropies are included. The new dispersion relation allows the treatment of more general space plasma equilibria such as the Dory-GuestHarris (DGH) or Kennel-Ashour-Abdalla (KA) loss cone equilibria, as well as distributions with power law velocity dependence that are modeled by the family of k-distributions. Under these conditions, we derive the general kinetic mirror instability growth rate including finite electron temperature effects. As for an example of equilibrium particle distribution, we analyze a large class of k to suprathermal loss cone distributions in view of application to a variety of space plasmas like the solar wind, magnetosheath, ring current plasma, and the magnetospheres of other planets.

Abstract. The theory of ionospheric Alfv6n resonator (IAR) and IAR feedback instability is reconsidered. Using a. simplified model of the topside ionosphere, we have reanalyzed the physical properties of the IAR interaction with magnetospheric convective flow. It is found tha, t in the absence of the convective flow the IAR eigenmodes exhibit a strong da, mping due to the leakage of the wa,ve energy through the resonator upper wall and Joule dissipation in the conductive ionosphere. It is found that maximum of the dissipation rate appears when the ionospheric conductivity approaches the "IAR wave conductivity" and becomes infinite. However, the presence of Hall dispersion, associated with the coupling of Alfv•n wave modes with the compressional perturbations, reduces the infinite damping of the IAR eigenmodes in this region and makes it dependent on the wavelength. The increase in the convection electric field lea, ds to a. substantial modification of the IAR eigenmode frequencies a. nd to reduction of the eigenmode damping rates. For a given perpendicular wa,velength the position of inaximum damping rate shifts to the region with lower ionospheric conductivity. When the convection electric field approaches a certain critical va,lue, the resona,tor becomes unstable. This results in the IAR feedback instability. A new type of the IAR feedba, ck instability with the lowest threshold value of convection velocity is found. The physica,1 mecha, nism of this instability is similar to the Cerenkov radiation in collisionless plasma,s. The favorable conditions for the insta, bility onset are realized when the ionospheric conductivity is low, i.e., for the nighttime conditions. We found that the lowest value of the marginal electric field which is ca, pa, ble to trigger the feedback instability turns out to be nearly twice smaller tha, n tha,t predicted by the previous analysis. This effect may result in the decrease of the critical value of the electric field of the magnetospheric convection tha,t is necessary for the forma, tion of the turbulent Alfv•n boundary layer and appearance of the a, nomalous conductivity in the IAR region.