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

Abstract.We use the first measurements of the STAFF/DWP instrument on the Double Star TC-1 spacecraft to investigate whistler-mode chorus. We present initial results of a systematic study on radial variation of dawn chorus. The chorus events show an increased intensity at L parameter above 6. This is important for the possible explanation of intensifications of chorus, which were previously observed closer to the Earth at higher latitudes. Our results also indicate that the upper band of chorus at frequencies above one-half of the electron cyclotron frequency disappears for L above 8. The lower band of chorus is observed at frequencies below 0.4 of the electron cyclotron frequency up to L of 11-12. The maxima of the chorus power spectra are found at slightly lower frequencies compared to previous studies. We do not observe any distinct evolution of the position of the chorus frequency band as a function of L. More data of the TC-1 spacecraft are needed to verify these initial results and to increase the MLT coverage.

Abstract. LFEW is a low frequency electromagnetic wave detector mounted on TC-2, which can measure the magnetic fluctuation of low frequency electromagnetic waves. The frequency range is 8 Hz to 10 kHz. LFEW comprises a boommounted, three-axis search coil magnetometer, a preamplifier and an electronics box that houses a Digital Spectrum Analyzer. LFEW was calibrated at Chambon-la-Forêt in France. The ground calibration results show that the performance of LFEW is similar to that of STAFF on TC-1. The first results of LFEW show that it works normally on board, and that the AC magnetic interference of the satellite platform is very small. In the plasmasphere, LFEW observed the ion cyclotron waves. During the geomagnetic storm on 8 November 2004, LFEW observed a wave burst associated with the oxygen ion cyclotron waves. This observation shows that during geomagnetic storms, the oxygen ions are very active in the inner magnetosphere. Outside the plasmasphere,