T.A.Yahnina, E.E.Titova, A.G.Yahnin, B.B.Gvozdevsky, A.A.Lyubchich (Polar Geophysical Institute, Apatity, Russia)

V.Yu.Trakhtengerts, A.G.Demekhov (Institute of the Applied Physics, Nizhny Novgorod, Russia)

J.L.Horwitz (The University of Alabama, Huntsville, Alabama, U.S.A.)

 The low-altitude NOAA satellites sometimes observed sharp, step-like enhancements in the trapped flux of energetic (E> 30 keV) electrons at L=3-5. In such events the flux increased for 150-300% when the latitude increased only for 0.1-0.3 degree. Closely to these features the localized bursts of precipitating energetic electrons were also observed. Relationship between the trapped and precipitating flux in such events, dependence of their occurrence on MLT, and particle flux dynamics during magnetic disturbances were considered. It was found, particularly, that in 80 percents of such events the step-like gradients in trapped (at the altitude 850 km) population and bursts of precipitation were observed in the evening sector. The events occurred mainly during the magnetic storm recovery phase. Nearly simultaneous data obtained from the NOAA and Aureol-3 satellites demonstrated the close relationship between these particle features and enhanced level of the ELF waves in the frequency range 100-1000 Hz. Comparison with the DE-1 satellite measurements of the low energetic (E<50 eV) ions showed the coincidence of the energetic electron precipitation features with the cold plasma gradients. These experimental results could be explained by the cyclotron instability developing in the vicinity of the plasmaspheric bulge or in the vicinity of some cold plasma gradients generated in the inner magnetosphere in the course of the magnetic storm.

V.Yu.Trakhtengerts*, A.A.Lyubchich**, A.G.Demekhov*, E.E.Titova**, M.J.Rycroft***

* Institute of Applied Physics, Nizhny Novgorod, Russia

** Polar Geophysical Institute, Apatity, Russia

*** International Space University, Strasbourg, France

Formation of a precipitation zone of energetic electrons by their injection into a region of enhanced background plasma density during magnetic storms is analyzed. Such a region can be formed by a plasmasphere bulge or detached cold plasma clouds appearing in the outer magnetosphere by the plasmasphere restructuring during a magnetic storm. As a mechanism of precipitations, wave-particle interactions by the cyclotron instability are considered. In framework of self-consistent equations of the quasi-linear plasma theory, the distribution function of trapped particles and spectral energy density of waves are found. Preliminary comparison of the theory with experimental data from NOAA satellites is made.

B.O.Vugmeister, R.A.Rakhmatulin, L.A.Leonovich, Yu.V.Lipko and I.V.Tabanakov (Institute of Solar-Terrestrial Physics SD RAS, Irkutsk 664033, P.O. Box 4026, Russia)

M.Goncharova and W.Lyatsky (Polar Geophysical Institute, Apatity 184200 Russia)

 The efficiency of the VLF wave frequency modulation by a magnetosonic low frequency wave as a function of magnetosphere plasma parameters is studied. Weak pitch angle diffusion of electrons into the loss cone is assumed. It is shown that in the quiet magnetosphere the disturbance of the maximum intensity frequency would be of order of or higher than the relative magnetic field disturbance in the equatorial plane. The upper cutoff frequency modulation is also considered. The frequency modulation seen on the calculated theoretical sonagrams may be related to the "non-dispersive" and to the "inverted V" structures of QP hiss. Simple formula relating the maximum intensity frequency and the magnetosphere plasma parameters in the equatorial plane is obtained. The relationship between the frequency modulation in the equatorial plane and on the ground is also calculated.

M.G.Gudkov (Arctic and Antarctic Research Institute, St.Petersburg)

A development of the Kelvin-Helmholtz instability in the compressible plasma containing a magnetic field is studied for a finite thick layer with a velocity shear in a linear two-dimensional MHD approximation. It is shown the existence some modes of oscillations connected with the different resonant points. The speed of the main flow in these resonant points differs from phase speed of oscillation by certain quantities typical of plasma, such as Alfven speed, fast and slow magnetosonic speeds, cusp resonance speed.

 For the velocity profile with the strongly expressed maximum of second derivative of the velocity, analytical expressions for the phase speed, growth rate and wavenumber of the fastest growing unstable mode have been obtained. These expressions have been applied with some necessary simplifications to regions of magnetisphere where sheared plasma flows are observed such as magnetopause, boundary between inner plasma sheet and plasmasphere.

V.Yu.Trakhtengerts, A.G.Demekhov (Institute of the Applied Physics, Nizhny Novgorod, Russia)

R.D. Belian (Los Alamos National Laboratory, Los Alamos, NM, USA)

J.Manninen, T.Turunen (Sodankyla Geophysical Laboratory, Sodankyla, Finland)

R.Rasinkangas (Department of Physical Sciences, University of Oulu, Oulu, Finland)

The peculiarities of the drift of energetic electrons injected during the substorm occurred in the beginning of December 17, 1990 were considered on the basis of the measurements made onboard three geosynchronous LANL satellites and CRRES. It was shown that for this event a simple model of electron cloud drift in the dipole-like magnetic field is appropriate to describe the observed evolution of the flux intensity. Pitch-angle anisotropy of the particles was considered, and it was shown that the anisotropy is maximal in the early morning sector in comparison with the night and late morning sectors. Comparison of the observations with the modeling of the pitch-angle distribution allowed us to conclude that in the morning sector the isotropization of the pitch-angle distribution as well as the precipitation of the electrons into the ionosphere probably occurred. Simultaneously, the impulsive electron precipitation and the VLF emissions were observed in the morning sector by the EISCAT radar and the ground-based VLF receiver, respectively. These observations were interpreted as signatures of the cyclotron instability developing in the equatorial magnetosphere. The characteristics of the impulsive precipitation could be related to the oscillating regime of the instability and the evolution of the pitch-angle distribution of the drifting particles.

A.G.Demekhov*, A.A.Lyubchich**, V.Yu.Trakhtengerts*, E.E.Titova**, A.G.Yahnin**

J.Manninen***, T.Turunen***

* Institute of Applied Physics, Nizhny Novgorod, Russia

** Polar Geophysical Institute, Apatity, Russia

*** Sodankyla Geophysical Observatory, Sodankyla, Finland

For comparison of theoretical results with experimental data, it is obviouly fruitful to employ simplified models which enable one quick obtaining of estimations and thus quick choosing of parameters providing the best agreement with the experiment. In this paper one of the models for a nonstationary regime of the whistler cyclotron instability is discussed. It is based on the so-called multi-level set of equations for the cyclotron maser (Bespalov, 1981), taking into account nonlinear modulation of the pitch-angle distribution of trapped particles. To get the model closer to the experiment, its generalized version with slow time dependence of the coefficients is considered. Such a dependence can be, e.g., due to variation of the number density, energy or anisotropy of energetic particles or background plasma density in the instability region. On the base of numerical calculations, we investigate the dependencies of characteristics of energetic electron precipitation pulsations on those parameters and their possible temporal evolution. An attempt is made to compare the results obtained with observational data.

The VLF wave modulation by Pc1/2 pulsations in the magnetosphere as a function of plasma parameters

M.Yu.Goncharova and W.Lyatsky (Polar Geophysical Institute, Apatity 184200 Russia)

Pc1-2 magnetic pulsations are usually considered to be Alfven waves that do not interact with VLF waves. However when a circularly polarized Alfven wave propagates in the dipole geomagnetic field along the flux tube the latter bends alternately into the area of weak and strong ambient magnetic field. As a result the VLF growth rate inside this flux tube would respond to the magnetic field compressions and decompressions. The efficiency of the Pc1/2 - VLF interaction is calculated as a function of the magnetosphere plasma parameters. It is shown that two main factors control the VLF wave intensity modulation by Pc1/2 pulsations: i) the compensation effect when integrating the VLF growth rate along the magnetic field line because of the short period of pulsations and ii) the combination of the electron pressure anisotropy A, and the squared ratio of the electron thermal velocity to the Alfven velocity B. It is found that for relatively quiet magnetosphere conditions at L=5, for A=0.5, B=1, Pc1-2 amplitude 5nT in the magnetosphere equatorial plane and the pulsation period of 7 s the expected VLF intensity variation would reach 1.5 times.

V.R.Tagirov, V.S.Ismagilov, E.E.Titova and A.A.Perlikov (Polar Geophysical Institute, Apatity, Murmansk region)

V.A.Arinin (Russian Federal Nuclear Center, Sarov, Nizhny Novgorod region)

J.K. Manninen, T.Turunen (Geophysical Observatory, Sodankyla)

K.Kaila (Department of Physics, University of Oulu, Oulu)

 Results of simultaneous TV observations of pulsating auroral patches and VLF-emissions in the morning sector carried out in Sodankyla (Finland) on February 15, 1991 are presented. Auroral pulsating activity was high during recovery phase of substorm and looked typical representing pulsating patches with characteristic periods about 5-10 s expanding and propagating during their brightening. Chorus elements in frequency range 1-2 kHz with typical periods of 0.3-0.4 s were the main VLF emissions at the same time. They appeared in trains with periodicity (5-10 s) the same as auroral one. Both auroral and VLF activity lasted up to the dawn demonstrating coexistence of both phenomena for about 2 hours. Two intervals (20 and 37 seconds) were chosen for detailed computer analysis of auroral images and VLF waves. Mutual correspondence between the flashing of the patches and appearence of VLF chorus trains was found out in both intervals. Most often chorus emissions coincide with the moments of maximum brightness of the patches. The spatial dimensions of pulsaing area were about 30 km luminosity propagated inside it with velocity about several km per second.

 This study has been supported by the grant 95-05-14495 from the Russian Foundation for Fundamental Research and INTAS grant 2753 & 3120.

I.A.Kornilov (Polar Geophysical Institute, Apatity)

 Three types of data analyzes have been used for the study of TV records with the fast auroral flashers and synchronously recorded VLF-chorus emissions (correspondingly 1350 and 1400 cases in total):

O.A.Maltseva (Institute of Physics, Rostov-on-Don)

E.E.Titova (Polar Geophysical Institute, Apatity)

V.Yu.Belashov (ISIP, FE Division of RAS, Magadan)

V.Yu.Belashov (ISIP, FE Division of RAS, Magadan)