Physics of auroral phenomena : proceedings of the 34th Annual seminar, Apatity, 01 - 04 March, 2011 / [ed.: A. G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2011. - 231 с. : ил.

Properties of the backward wave oscillator model of VLFchorus generation inferred from CLUSTER measurements density we determined the values and variations of the q parameter in the generation region. The results of numerical simulations of chorus elements based on the BWO model are in accord with the values of the q parameter obtained from the CLUSTER data. Significant scatter of the q parameter values was observed during each Cluster passage of the generation region. Parameter q , characterizing the step-like deformation of the distribution function of energetic electrons, is proportional to the height of the step and the concentration of energetic electrons. Therefore, we assume that significant scatter of the q parameter characterizes the scatter in the step parameters. We believe that further analysis of the q parameter on the basis of CLUSTER data along with the data on the flux of energetic electrons will allow us to improve the understanding of the electron distribution function dynamics in the chorus generation region. Acknowledgments. The present work was supported under the GACR grant 205/10/2279, the ME 10001, the RFBR (grants 11-02-00654, 11-02-00397, RFBR- CNRS N10-02-9311), and the Program of RAS “Plasma Processes in Solar System”. The Iowa co­ authors acknowledge support from NASA Goddard Space Flight Center under Grants NNX07AI24G and NNX11AB38G. References 1. V. Y. Trakhtengerts, “Magnetosphere cyclotron maser: Backward wave oscillator generation regime”, J. Geophys. Res., 100, 1995, p. 205-210. 2. V. Y. Trakhtengerts, “A generation mechanism for chorus emission”, Arm. Geophys., 17, 1999, p. 95- 100 . 3. A. G. Demekhov, V. Y. Trakhtengerts, М. M. Mogilevsky, L. M. Zelenyi, “Current problems in studies of magnetospheric cyclotron masers and new space project “Resonance” Adv. Space Res., 32(3), 2003, p. 355-374. 4. E. Macusova, et al., “Observations o f the relationship between frequency sweep rates of chorus wave packets and plasma density”, J.Geophys. Res., 115, 2010, doi:10.1029/2010JA015468. 5. V. Y Trakhtengerts, A. G. Demekhov, E. E. Titova, В. V. Kozelov, O. Santolik, D. Gumett, and M. Parrot, “Interpretation of cluster data on chorus emissions using the BWO model”, Phys. Plasmas, 11, 2004, 1345-1351. 6. A. A Bespalov, and A. G. Demekhov, “A linear theory of the backward-wave-oscillator regime in the magnetospheric cyclotron ELF/VLF maser”, Radiophys. Quantum Electron. 52(11), 2009, p.761- 773. 7. D. A. Gumett, et al., “First results from the Cluster wideband plasma wave investigation”, Ann. Geophys., 19, 2001, p. 1259-1272. 8. P. M. Decreau, et al., “Early results from the Whisper instrument on Cluster: An overview”, Ann. Geophys., 19, 2001, p.1241-1258. 9. A. G Demekhov and V. Y. Trakhtengerts, “Dynamics of the magnetospheric cyclotron ELF/VLF maser in the backward wave oscillator regime. II. The influence of the magnetic field inhomogeneity”, Radiophys. Quantum Electron. (Engl. Transl.), 51(11), 2008, p. 977-987. 93