O.V. Kozyreva, N.G. Kleimenova (Institute of the Earth Physics RAN, Moscow)

P. Francia, U. Villante (University of L'Aquila, Italy)

M. Bitterly (Institute of the Earth Physics, Paris)

J. Schott (E.O.S.T., Strasbourg, France)

Simultaneous long-term geomagnetic pulsation measurements by two on-ground stations in Antarctica, located at similar geomagnetic latitudes ~80.5 S with longitude distance about 5 hours has been analyzed. It was found, that the daytime 0.6-6.0 mHz spectral wave distribution was similar at both stations and showed the rapid decrease of the intensity with frequency in the range of 1-2 mHz and the broad enhancement between ~2 -5 mHz, often with remarkable maximum in the frequency band of about 2-3 mHz. The ipcl pulsations looked like the background noise with separated wave packets in which the time signature of the frequency bands of ~1-2 mHz and ~2-3 mHz could be different as well as similar. The waves propagated from noon till morning with significant attenuation which was greater for 1-2 mHz than for 2-3 mHz. Counter-sunward propagation for both 1-2 mHz and 2-3 mHz bands, the near noon polarization rotation reversal and noon enhancement of the amplitudes indicate a common generation mechanism for all frequencies of pulsation of the given event, but each wave packet is caused by different impulsive source. The ipcl could probably represent the superposition of waves of different nature.

S.I. Solovyev, D.G. Baishev, E.S. Barkova

(Institute of Cosmophysical Research and Aeronomy, Yakutsk, Russia)

K. Yumoto (Kyushu University, Fukuoka 812-81, Japan)

M.J. Engebretson (Augsburg College, Minneapolis, MN 55454-1338, USA)

W.J. Hughes (Department of Astronomy and Center for Space Physics, Boston, MA 02215, USA)

GEOTAIL satellite data obtained during N-S aurora show that their formation is accompanied with fluctuations of the electric field (E_y) and particle fluxes in the direction to the Earth (V_x) with quasiperiods of ~5-15 min. On the basis of these observational facts we assume: (1) the Cowling currents along the auroral luminosity band stretched along the meridian contribute mainly to Ps6 currents; (2) the formation of N-S aurora which can be simultaneously observed with a generation of omega bands gives evidence of turbulent processes in the plasma sheet and the generation of BBF-events.

E.Yu. Feshchenko (St-Petersburg State University, Russia)

Yu.P.Maltsev, A.A.Ostapenko (Polar Geophysical Institute, Apatity, Russia)

The database of Fairfield et al. [1994] has been used for drawing magnetic field lines in the magnetosphere at distances of 10 Re > x > -40 Re. The field of the magnetospheric currents was averaged in the cubic bins with the linear size of 2 Re. The total field is the sum of fields of the magnetospheric currents and of the Earth dipole. The magnetic field lines are built under various values of the Dst and Kp indices, solar wind dynamic pressure Psw, and vertical component of the interplanetary magnetic field BzIMF. The configuration of the magnetic field lines appeared to be most sensitive to the Dst and Kp. The latitude of the dayside polar cusp decreases by 1 degree when either Dst falls by 15 nT or Kp grows by 0.7. Such a decrease exceeds that in the model by Tsyganenko [1995] several times and agrees well with observations. Storms stretch the magnetotail, whereas substorms somewhat dipolarize it. The sizes of the magnetosphere as well as its day-night asymmetry depend mainly on the pressure Psw. The influence of BzIMF (providing Dst, Kp, and Psw keep invariable) appeared to be negligible.

О. В. Мингалев

Получена формула для плотности продольного тока, которая является обобщением известной формулы Василюнаса--Тверского, полученной при условии магнитогидростатического равновесия и изотропности давления, на случай, когда учитывается возможность анизотропии давления в разреженной горячей магнитосферной плазме. Полученная формула позволяет найти плотность продольного тока в данной точке в магнитосфере Земли, если во всех точках проходящей через данную точку силовой линии магнитного поля, лежащих между данной точкой и плоскостью экватора, известны величина магнитного поля, градиенты эйлеровых потенциалов магнитного поля и ортогональная к магнитному полю составляющая дивергенции тензора напряжений, а также известна плотность продольного тока в плоскости экватора.

Таким образом, учёт анизотропии давления разреженной горячей магнитосферной плазмы усложняет вычисление плотности продольного тока по сравнению со случаем изотропного давления, когда для вычисления плотности продольного тока в данной точке достаточно знать градиент давления в этой точке, распределение величины магнитного поля вдоль его силовой линии от плоскости экватора до рассматриваемой точки и плотность продольного тока в плоскости экватора.

Также обсуждается вопрос о нахождении эйлеровых потенциалов магнитного поля в магнитосфере.

I.V. Despirak, A.G. Yahnin, A.A. Lubchich (Polar Geophysical Institute, Apatity, Russia)

We have examined 31 crossings of polar orbiting TIROS/NOAA satellites over the polar cap sun-aligned arcs observed from the ground-based Antarctic station Vostok (Corr.Geom.Lat.=-84^O). For 88% of the crossings it has been found that the arcs are embedded into the wide region of the energetic (>30 keV) proton precipitation. For most cases the proton precipitation region is simply poleward extension of that observed at the auroral zone latitudes, but sometimes it is isolated from the auroral zone by the precipitation gap. We suggest that the energetic protons have the origin from the magnetospheric plasma sheet, where, as it is known, their fluxes are rather high in any geomagnetic conditions. This is particularly confirmed with consideration of a “spectral index”, which is a ratio of the proton flux at energies >30 keV and the flux at energies <20 keV. It has been shown that the spectral index of proton precipitation related to polar cap arcs is nearly the same as for that in the auroral zone. For some events we were able to observe the polar rain precipitation. The energetic proton precipitation region as well as auroral arcs embedded were found outside the polar rain area. On the basis of these findings we conclude that the polar cap auroral arcs are originated from the closed field lines inside magnetosphere.

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

J.Borovsky, M.Thomsen (LANL, Los Alamos, NM, USA)

In a series of recent papers /1, 2, 3, 4/ a new pattern of the low-altitude energetic electron precipitation, so called "precipitation cliff", has been described. This is a sharp spike of both precipitating and locally trapped particles, which is usually observed in the vicinity of L=4 in the evening sector. Both experimental and theoretical investigations suggest that the cliff phenomena relate to the cyclotron instability in the region where there is a sharp gradient in the spatial distribution of cold plasmaspherelike plasma.

To verify the suggestion that the cliff associates with the cold plasma gradients we compared the cliff observations from low-altitude NOAA satellites with the longitudinal distribution of the cold plasma observed at geosynchronous orbit. The cold plasma observations have been done using the MPA instrument onboard the geosynchronous LANL satellites (see, /5/ for details). Typically the plasmasphere population at L=6.6 is seen in the afternoon-evening sector and has rather sharp boundaries. The boundaries mark, evidently, the edges of the plasmaspheric plasma expanded sunward (or detached) in the afternoon-evening sector in form of a "tongue". The interpretation of the cliff phenomenon (see references above) suggests that it should appear at the western edge of the tongue. The mapping of NOAA orbits into the equatorial plane showed that the location of the cliff and the location of the western edge of plasmaspherelike plasma region detected by the LANL satellites are in a reasonable agreement with this view. We conclude that together with in situ cold plasma measurements the low-altitude energetic particle observations provide us with a tool for monitoring of the spatial configuration of the cold plasma region detached from the plasmasphere.

1. T.A.Yahnina, E.E.Titova, A.G.Yahnin, B.B.Gvozdevsky, A.A.Lubchich, V.Yu.Trakhtengerts, A.G. Demekhov, J.L.Horwitz, J.Manninen, T.Turunen. Some features of the energetic electron precipitation in the evening sector. Proceedings of XIX Apatity seminar "Physics of auroral phenomena", 70-72, Apatity, 1996.

2. V.Yu.Trakhtengerts, A. Lubchich, A.G.Demekhov, T.A.Yahnina, E.E.Titova, M.J.Rycroft, J.Manninen, T.Turunen. Cyclotron model for quasi-steady precipitation of energetic electrons at the plasmapause. Proceedings of XIX Apatity seminar "Physics of auroral phenomena", 73-76, Apatity, 1996.

3. E.E.Titova, T.A. Yahnina, A.G.Yahnin, B.B.Gvozdevsky, A.A.Lubchich, V.Yu.Trakhtengerts, A.G. Demekhov, J.L.Horwitz, F.Lefeuvre, D.Lagoutte, J.Manninen, T.Turunen. Strong localized variations of the low-altitude energetic electron fluxes in the evening sector near the plasmapause. Ann. Geophysicae 16, N1, p.25-33, 1998.

4. D.L. Pasmanik, V.Yu. Trakhtengerts, A.G.Demekhov, A. Lubchich, E.E.Titova, T.A.Yahnina, M.J.Rycroft, J.Manninen, T.Turunen. A quantitative model for cyclotron wave-particle interactions at the plasmapause. Ann. Geophysicae 16, N3, p.322-330, 1998.

5. M.B. Moldwin, M.F. Thomsen, S.J. Bame, D.J. McComas, K.R. Moore. An examination of the structure and dynamics of the outer plasmasphere using multiple geosynchronous satellites. JGR, V.99, N A6, 11475-11481, 1994.

V.E. Kunitsyn, I.V. Silin

(Moscow State University, Moscow, Faculty of Physics, Dept. of Atmospheric Physics)

The multi-spacecraft ROY project is designed to study the small-scale turbulent structures in the critical regions of the magnetosphere. These regions include polar cusps, subsolar magnetopause and earthward edge of the cross-tail current. The group of satellites in the project will consist of one main satellite (the BASE) and four subsatellites.

One of the main tasks of the ROY project is the radiotomographic reconstruction of 2D cross-sections of electron density in the regions mentioned above. As the most suitable method for the experiment the ray phase-difference medium wave tomography is proposed. According to recent in-situ measurements and some theoretical estimates the hot plasma inhomogeneties in the critical regions of magnetosphere are scaled according to ion Larmor radius, which is of the order of tens or hundreds of kilometers. Our estimates showed that with these typical spatial scales and the typical electron density ~10 cm-3 the probing and the bearing waves' frequencies f1 and f2 should be chosen in the range between 100-300 kHz and around 1 MHz respectively. The resolution of this method is limited with the Fresnel zone diameter which in our case is approximately 20 km.

Bulk velocities of plasma in investigated regions vary in the range between ~10 and ~200 km/s. Due to plasma motion radiowaves emitted under different angles in consequent moments will cross the same part of the scanned plasma formation and the trajectories of radio-rays connecting the BASE with different subsats will intersect. This way multiple crossings of investigated plasma structure with numerous intersections will be obtained by use of only three subsatellites. Taking this into account the following configuration for the RSS was proposed: all subsatellites are placed along the plasma streamline so that the angle between rays from the BASE to wing subsatellites makes at least 100 degrees.

A course of computer simulations of the experiment was carried out. As it is very difficult to predict what kind of structures may be encountered in the experiment the aim of the simulations was to test the proposed configuration in as many vairous types of electron density distribution as possible. Several examples of 2D cross-sections of electron density distribution in the regions of magnetic field reconnection obtained in 3D kinetic modeling by team of J. Buechner at Max Planck Institute for Aeronomy were used. The results of the simulations demonstrated perfect feasibility of the method for the investigated phenomena.

A.V. Dmitriev and A.V. Suvorova (Institute of Nuclear Physics, Moscow State University, Moscow, Russia)

The code of 3D Artificial Neural Network Model of Dayside Magnetopause is applied for description of the dynamics of subsolar point and cusp region under different solar wind and interplanetary magnetic field conditions. The dependence of the subsolar point location on the dynamic pressure and IMF Bz- and By- components is expressed in the form of modified logistic function which permits to describe three different regimes of magnetopause formation controlled by IMF Bz-component. The dynamics of the cusp region extension in longitudes and latitudes is presented. Effects of "dimple" formation in the region of the subsolar point and the cusp disappearance under strong negative Bz (<-10nT) are described.

M.A. Volkov (Murmansk State Technical University, Murmansk)

One of the possible mechanisms of formation of expansion phase currents of magnetospheric substorm is considered in the paper. According to the measurements in the plasma sheet during a substorm expansion phase the ions' density decreases but their temperature grows (1). These processes can be connected with reconnections of magnetic field lines. In the paper (2) the connection between magnetosheric substorm currents and region with the lowered density of the charged particles (hot magnetospheric ions) in the plasma sheet has been found, and field-aligned currents flow on edges of this region. In the present paper the given current system is received by calculation of the hydrodynamic equations system for hot magnetospheric particles when region of the lowered density of charged particles occurs in the plasma sheet. The system of the equations for the charged particles can be reduced to two-dimensional by integrating them along magnetic field lines. We allow that magnetic field lines are equapotential and pressure of plasma field lines is isotropic and constant. The numerical calculations are carried out for cases when in the initial time moment plasma pressure inside and outside of the region is identical and the field-aligned currents are absent. Characteristic time of current system development is 10-15 minutes.

This work has been supported by Grant ь 98-05-64145 of Russian Foundation of Basic Research.

1. W. Baumjohann, G. Paschumann, T. Nagai, H. Luhr Superposed epoch analysis of the substorm plasma sheet // J.Geophys.Res. 1991. V. 96. N A7. P. 11605

2. M.A. Volkov, A.A. Namgaladze Models of field-aligned currents needful to simulate the substorm variations of the electric field and other parameters observed by EISCAT//Annales Geophysicae. 1997, V.15, N1

A.A. Rusanov, T.M. Burinskaya, M.M. Mogilevsky, R.A. Kovrazhkin (Space Research Institute of RAS, Moscow, Russia)

J.-A. Sauvaud (CESR/CNRS, Toulouse, France)

In this presentation some results of the analysis of electromagnetic and electrostatic signals in the VLF frequency range measured at the INTERBALL-2 satellite are discussed. The satellite was equipped with wave instrumentation including the VLF receiver NVK-ONCH, which operates in the frequency range 8Hz - 20kHz and makes it possible to transmit to ground waveforms of electrical and magnetic components. The relevant particle data were taken from ION experiment, which measured ion and electron fluxes in the energy range of 10eV - 20 eV.

The INTERBALL-2 plasma wave instrument have currently shown two kinds of signals (i) in the polar cap and (ii) at the polar boundary of the auroral region. This emission in polar cap was associated of broadband whistler mode emissions (hiss) with a cut-off near the local plasma frequency, narrow band Langmuir oscillations modulated in ELF frequency range, and mixtures of both wave emissions. The Langmuir wave emissions are very short in time and often are composed of several electrostatic wave bursts. Langmuir emissions observed near the polar boundary of the auroral region are typically made of a series of bursts with average pulse duration about 0.1 - 0.4 sec. On contrary Langmuir wave activity observed in the polar cap usually presents 1 - 3 bursts with duration 1 - 3sec.

The series of electrostatic bursts detected at the polar boundary of auroral region were observed in association with fine structured electron fluxes that are typical for this region. The long duration emissions in the polar cap are associated with hot plasma clouds detected by particle measurements in the cold polar cap plasma environment. However the typical time of cloud registration at the spacecraft is about several minutes, though the characteristic duration of the polar cap electrostatic bursts is about few seconds.

Physical mechanisms of detected phenomena are discussed in term of guided plasma waves propagation.

M. Goncharova, W.Lyatsky, V.Kriviliov (Polar Geophysical Institute, Apatity, Russia)

D. G.Sibeck (APL/JHU, Laurel, Maryland, USA)

The separation of the dispersion signatures measured onboard DMSP F7 to those forming the average energy decline (hereafter general dispersion signatures) and those forming the dispersion fine structure allowed to obtain new information about relationship between the IMF B_z component and dispersion-forming velocity. Particularly it was found that for the general dispersion signature:

1) for IMF B_z southward the meridian component of the dispersion-forming velocity drops with increasing IMF Bz whereas for IMF B_z northward it has poleward and equatorward branches due to measurements in counter-dispersive general signatures, the either of them increasing with IMF B_z growth;

2) the distribution of those velocities and sites of their measurements over the local time and latitude imply they would reflect the two convection mechanisms - for open and closed field lines - working together at higher and lower latitudes respectively. So far, the counter-dispersive general signatures could be supposed as reflecting the meeting of the counter-directed ionosphere convection flows.

L. Benkevich, W. Lyatsky (Polar Geophysical Institute, Apatity, Russia)

This work presents some results of model study of the magnetospheric field-aligned currents (FACs) that flow between the north and the south parts of the ionosphere. Magnetospheric sources produce "primary" FACs, they diverge in the ionosphere, branching into the secondary interhemispheric currents. These currents emerge in the vicinity of ionospheric conductivity discontinuity lines such as the terminator. To explore this phenomenon, two 3-dimensional current system models have been developed, analytical and numerical ones. Using the both, we obtained the conditions under which the secondary currents get substantial. Then we conducted a series of numerical experiments to obtain their distributions and to determine what fraction of the primary currents branches into the secondary interhemispheric currents.

A.A.Ostapenko, Yu.P.Maltsev (Polar Geophysical Institute, Apatity)

V.G. Vorobjev, B.V. Rezhenov, G.V. Starkov (Polar Geophysical Institute, Apatity, Russia)

L.I. Gromova, Ya.I. Feldstein (Institute of Terrestrial Magnetism, Ionosphere and Radio Waves Propogation, RAS,Troitsk, Russia)

A.G.Yahnin (Polar Geophysical Institute, Apatity, Russia)

N.L.Borodkova, A.A.Petrukovich, A.O.Fedorov (Space Research Institute, Moscow, Russia)

L.A.Frank (Dept of Physics & Astronomy, University of Iowa, Iowa City, USA)

T.Mukai (Institute of Space and Astronautical Science, Sagamihara, Japan)

M. A. Volkov (Murmansk State Technical University)

Yu. P. Maltsev (Polar Geophysical Institute, Apatity)

The paper [1] shows that the magnetosphere-ionosphere convection causes interchange instability everywhere in the plasma sheet, even at its inner boundary. As a result, electric field and field-aligned current structures are formed. They are stretched approximately along the east-west direction. This instability allows to explain generation of discrete auroral forms. The paper [1] considered the magnetospheric plasma to be monoenergetic. Now we have taken into consideration the thermal spread. General dispersion equation for the interchange instability is obtained for an arbitrary distribution function. For special cases of rectangular and triangular functions, analytical solutions are found. Dependence of growth rate of the instability on the wave vector is investigated. The time of development of the instability appeared to be about 5-10 minutes.

[1] M.A. Volkov, Yu.P. Maltsev, Interchange instability of the inner plasma sheet boundary, //Geomagn. Aeron., 26, 798-801, (in Russian), 1986.

Обращается внимание на связь инвариантности уравнений идеальной одножидкостной МГД относительно калибровочных преобразований 4-потенциала и 4-импульса с интегрируемостью уравнений движения Эйлера и уравнений течения. Показано, что появление (в результате калибровки) новых вмороженных полей приводит к появлению новых, не обсуждавшихся ранее лагранжевых инвариантов.

Y. V. Bogdanova, V. S. Semenov (Physical Institute, St.Petersburg State University, Russia)

R.P. Rijnbeek, M. J. Buchan (Space Scientific Center, University of Sussex, Brighton BN1 9QH, UK)

A new interpretation of active arc dynamics at the polar boundary of auroral bulge during the expansion phase of a substorm is presented. Investigation was made in the conditions of the model of magnetic reconnection in the magnetosphere. This model is based on the hypothesis about magnetic reconnection in the magnetotail current sheet. The main processes responsible for the breakup are assumed to take place in the vicinity of the neutral X-line in the magnetotail, and the associated auroral dynamics can be interpreted as the ionospheric manifestation of magnetotail reconnection.

We suppose that auroral arc is a result of following processes:

1). Reconnection pulse in the magnetotail current sheet leads to generation of Alfven shock wave. Electrons are accelerated on the shock wave front up to the thermal energy.

2). Alfven wave propagates along magnetic field lines into the ionosphere and induces Birkeland current system. Upward field-aligned current is formed in the nightside sector.

3). The main acceleration electrons have in the region of field-aligned potential difference at the altitudes of about (1-2)R_E over ionosphere at auroral field lines.

Shock wave propagates through magnetotail with local Alfven velocity, and non-uniform plasma medium leads to the dispersion of the wave. Numerical simulations show that in this case manifestation of magnetotail reconnection can correspond to both poleward and equatorward moving auroral arc. Dynamics of auroral arc depends on three parameters: the dissipative electric field in the diffusion region, the gradient of the Alfven speed in the magnetotail and the position of the X-line in the current sheet.

To illustrate this idea two experimental keograms showing interesting active arc dynamics (double arcs and series of equatorward moving arcs) during breakup are presented. Our investigation shows a good agreement of dynamics deduced from our model with these experimental keograms.