T.A.Kornilova, I.A.Kornilov (Polar Geophysical Institute, Apatity, Murmansk region, 184200 Russia),

M.I.Pudovkin (Institute of Physics,University of St Petersburg, St Petersburg, 198904 Russia),

K.Kaila (Department of Physics University of Oulu, Linnanmaa, FIN-90570 Oulu, Finland),

J.Manninen, J.Kultima (Geophysical Observatory of the Finnish Academy of Science and Letters, FIN-99600 Sodankyla, Finland)

 Regularities in behavior of arcs on the pole boundary of auroral oval during substorm active phase have been investigated on the base of TV data. Different ways of poleward expansion are described. Besides known earlier persistent and jump poleward spreading there are some others: splitting of fine arcs from the front of the poleward mowing arc and their following movement poleward; forming of the pole arc from the weak diffuse luminosity occurring at higher latitudes; forming of the pole arc by bright local formation separated from a primary existing pole arc and moving parallel to the latter. The velocity of poleward expansion has been estimated. It is shown that the typical feature of auroral dynamics of poleward expansion is regular decrease in velocity. As the velocity decreases the local maxima appear. Statistic results of study of horizontal luminosity profiles of arcs on the pole boundary of auroral oval are presented. It is shown that profiles of motionless and poleward moving arcs are generally symmetrical, and profiles of equatorward moving arcs are asymmetrical with smaller tilt in the direction of their motion.

V.O.Papitashvili, C.R.Clauer (Space Physics Research Laboratory, University of Michigan, Ann Arbor, USA)

E.Friis-Christensen (Danish Meteorological Institute, Copenhagen, Denmark)

S.-I.Ohtani (The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA)

Magnetic data from meridional chain of stations in Greenland and AL - indices of magnetic activity are used to study the relationship between magnetic perturbations in the daytime cusp/cleft region and substorm development. The only events analysed are those for which the Greenland West Coast chain is in the noon sector, and there is substorm activity in the nighttime auroral zone. 14 substorms developed under conditions of positive or close to zero IMF Bz component and large positive or negative By component were chosen for analysis. It is shown that the current intensification in the cleft region preceds or accompanies the substorm development and is observed for both signs of IMF By. To explain this relationship between the cleft currents and the auroral electrojet, an interconnection between the plasma sheet currents and the noon Birkeland current system is suggested and discussed. The field-aligned current patterns derived from magnetic measurements on board DMSP F7 spacecraft for case of two substorms are compared with the patterns obtained from ground magnetic observations.

L. Lazutin (Polar Geophysical Institute, Russia)

 From the numerous experimental studies it is known, that during the auroral breakup following effects are taking place in the vicinity of the geosinchronous orbit: (1) magnetic field configuration is changing from stretched tailward toward more dipolar and growing by value, (2) auroral and radiation belts electron are accelerated in wide range of energies, and(3) radial tailward transport of electrons is taking place. Particle transport and acceleration are calculated in present paper using Tsiganenko(89) magnetic field models. Some modification were introduced to create more realistic tailward magnetic field line stretching before the breakup.

 Computer program of successive transition between the pairs of magnetic field models corresponding to the situation before and after the breakup includes calculation of the inductive electric field, ExB and magnetic drift velocities and other parameters.

 Following conclusions results from the modelling:

(1) calculated electron acceleration is sufficient as compared with the experimental data;

(2) electrons initiated at 5-9 Re are moving presumably tailward whereas more distant particles are transported earthward;

(3) drift-shell splitting effect separate electrons with different energies; final position of the particles with smaller pitch angle is closer to the Earth;

(4) pitch angles of the electrons increases during magnetic field dipolarization.

All this effects are in agreement with the scenario of the substorm initiation on closed field lines in geosynchronous region.

E.E.Antonova, N.Yu.Ganyshkina, I.L.Ovchinnikov (Skobeltsyn Institute of Nuclear Physics Moscow State University, Moscow)

 The magnetosphere electric fields and currents dynamic theory is developed based on the suggestion of magnetostatic equilibrium support in the inner magnetosphere and inner plasma sheet regions. The theory give the possibility to explain the auroral oval projection on the inner plasma sheet regions and IMF control of magnetospheric convection. The dawn-dusk electric field is formed due to Region 1 field-aligned current generation and their closing in the auroral ionosphere. Region 1 currents are supported by azimuthal plasma pressure gradients along the magnetic flux tube isosurfaces. The created dawn-dusk field is projected on the tail field lines and creates lobe plasma flow to the equatorial plane. The theory of plasma sheet equilibrium formation taking into consideration middle-scale electric fields and diffusion plasma sheet processes give the possibility to determine plasma pressure dependence on magnetic field vector potential and to solve Grad-Shafranov equation. On the base of plasma sheet turbulent model it is possible to explain the plasma sheet dynamics during substorm including plasma sheet thinning during the substorm growth phase and plasma sheet thickening during substorm expansive phase. These properties are connected with turbulence spectrum change and dawn-dusk electric field dynamics. The beginning of substorm expansive phase in the inner magnetosphere regions is explained on the base of transverse currents dynamics during IMF Bz<0.

V.V. Safargaleev, W.B. Lyatsky, V.R. Tagirov (Polar Geophysical Institute, Apatity 184200, Russia)

The variations of the luminosity of several parallel auroral arcs before the auroral breakup was studied by using digitised TV-data (obs. Loparskaya). The events of short-time activisation at least one of the arcs few minutes before the substorm onset (pseudobreakup events) were chosen for the analysis. All the events may be separated into two groups. The events of the first group are characterised by simultaneous enhancement of intensity in the all arcs (S-events). The events of the second group are characterised by opposite behaviour of the arc intensity when the brightening of one arc is accompanied by fading or disappearance of other arcs (O-events). Some times O-event shows itself as a jump-like (from arc to arc) equatorward movement of the luminosity with the velocity of about 4 km/s at the ionosphere altitude. The character time of the S-events is of about 15 s. The O-events last more than one minute. As the local activisation of one of the arc (pseudobreakup) may be caused by the magnetic field lines reconnection in the magnetotail, the counterphase variations of the luminosity in several arc may testify that the beginning of magnetic field lines reconnection in one place in the magnetotail prevents from the reconnection development in any other place.

T.V.Kozelova, L.L.Lazutin, B.V.Kozelov (Polar Geophysical Institute, Apatity, Russia)

R.Rasinkangas (University of Oulu, Oulu, Finland)

One of problems concerning substorm is the determination of the location of the substorm onset region. This issue presents the CRRES magnetometer and energetic particle data obtained during the substorms on Feb 9 and 28, 1991. CRRES data are used to examine the spatial evolution of the flux enhancement regions relative to the spacecraft during the substorm onset and the local magnetic field dipolarization. The 37-190 keV proton fluxes observed by EPAS spactrometer exhibited strong azimutal anisotropy during an individual spin period (30s). This anisotropy can be interpreted in terms of spatial gradients of substorm associated particle fluxes. The following main points can be seen from the CRRES data: (1) The noncoherence of the proton flux variations within a small spatial region (2gyroradii). (2) Anisotropy of the higher energy proton fluxes may differ from the anisotropy of the low energy proton fluxes. (3) Local magnetic field dipolarization was accompanied by large dispersive 85-190 keV proton flux increase tailward of the spacecraft. (4) Increase of 37-70 keV proton fluxes eathward of the spacecraft was associated with reconfiguration of the magnetic field to a more taillike. This analysis shows the rapid dynamical variations of different regions of proton flux enhancements during magnetospheric substorm.