Y.I. Feldstein (IZMIRAN, 142092 Troitsk, Moscow Region, Russia)

Recently PGI and MSU-IZMIRAN offered two ways of researches of contributions of various magnetic field sources to the ground magnetic field variations. There are the magnetosphere paraboloid model by Alexeev et al. and Maltsev et al. method. Both ways were used for magnetic storms intervals. For two magnetic storms with all necessary for both methods implementation data available, the corresponding calculations of ground magnetic field were conducted. Their results are compared with the observed Dst-variation. The previous conclusions on necessity of allowing for tail currents magnetic field, when ground magnetic field variations during magnetic storms are interpreted, are substantiated.

B.V. Rezhenov, Yu.P. Maltsev (Polar Geophysical Institute, Apatity, 184200, Russia)

We have studied the response of the hourly Dst index to the IMF Bx and By components in several ranges of the IMF Bz. Processing the data throughout the 28 year period showed no distinct dependence of the response of Dst on the IMF Bx and By in all the ranges of Bz. At the same time the dependence on Bz is clearly seen at any By. Hence one can conclude that the storm activity is controlled by the magnetic flux transport from the dayside to the magnetotail rather than by the energy input into the magnetosphere.

Yu.P. Maltsev (Polar Geophysical Institute, Apatity, 184200, Russia)

A.A. Ostapenko, Yu.P. Maltsev (Polar Geophysical Institute, Apatity, 184200, Russia)

We used 60,000 magnetic measurements from the database of Fairfield et al. [JGR, 1994, V.99, 11319] for studying the differential responses of the magnetic field at distances of -30 Re < X < 10 Re to changes in the Kp and Dst indices. The response to a change of the substorm-related Kp index manifests itself almost completely as intensification of the cross-tail electric current. The change of the storm-related Dst index results in increasing of both the cross-tail and ring currents. An interesting peculiarity of the storm time depression is the absence of positive variation of the magnetic z-component throughout the magnetosphere that evidences the dominant role of the cross-tail current.

M.G. Gelberg, S.Z. Kershengolz, L.P. Shadrina, S.V. Sharaeva

The correlative relation between the absolute value of Dst min in the period of the main phase of sporadic and two groups of recurrent storms with frequencies of AE-index bursts has been investigated. A duration of these bursts was less than 10 min and deviations from background magnitudes of AE were more than 80, 150, 200, 250, 300 nT. The linear relation indices (correlation coefficients) were calculated for each group of storms as well as for all 133 events. Nonlinear relation indices between Dst min and fj were calculated only for the joined sampling.

For all j the high correlation coefficients of Dst min with fj were found to be 0.7 for the sporadic storms, 0.3 for recurrent storms of A-group and 0.5 for B-group. For the total sampling the linear relation indices are close to values for sporadic storms that testifies to the high interclass correlation between Dst min and fj for all classes of storms. For f1 and f2 a nonlinear measure of relation essentially more than the correlation coefficient, and for f>3 the indices of nonlinear and linear relation are practically not differ.

Existence of the relation between Dst min in the period of the main storm phase and the intensification frequency has been explaned as the influence of inductive electric fields at the magnetosphere equator on a transport of energetic electrons from the near part of the tail to the stable capture region. It is shown that the ring current is enhanced if an amplitude of magnetosperic intensifications in AE-index more than 250 nT for sporadic and 150 nT for recurrent storms of B-group.

This work was support Russian Fundamental Research Fund, grant N 95-05-14329.

M.G. Gelberg (Institute of Cosmophysical Research and Aeronomy. 31 Lenin Ave., 677891 Yakutsk, Russia)

Relationships between AE-index in the end of growth phase (AEp) and at a maximum of expansion (AEm) phase for the substorms with the sharp onset of expansion phase and their correlation with solar wind parameters have been analyzed. Four classes of substorms were selected: spontaneously developed substorms at Bz < 0 (class 1) and at Bz > 0) (class 2), substorms initiated by the fast change of Bz sign from minus to plus (class 3) and substorms initiated by the sharp change of the IMF By-component (class 4). Events of each class were separated into groups according to the background disturbance level before an onset of the substorm expansion phase: high disturbance (group A), middle one (group B), weak one (group C). It is shown that for initiated substorms the influence of the disturbance level on AEp and AEm variations is approximately identical (correlation ratios was 0,35). For events of 1 and 2 classes (it was 0,36 for AEp and 0,21 for AEm. Correlation coefficients between AEp and AEm for all the classes are approximately equal to 0,75 - 0,8. However, for spontaneous substorms it was calculated for A-C groups are increased with a growth of the geomagnetic disturbance before a substorm.

For initiated substorms such dependence was not available. Mean values of AEp and AEm for events of class 2 were essentially smaller, and correlation coefficients between these characteristics and dynamic pressure of solar wind (equal to 0,61 and 0,55) are higher than for substorms the at Bz < 0. Substorms initiated by the sharp change of IMF By are observed at more high pressure of solar wind and have larger mean values of AEp and AEm than in the other classes.

The analysis of differences between substorm classes with the sharp onset shown that Layons hypothesis that as if practically all substorms has are initiated by the sharp change of interplanetary parameters, is most likely incorrect. For the class 1 events it is shown that AEp and AEm weakly correlate with parameters of a type of the Akasofu epsilon-parameter. This is evidence for the nonergodicity of auroral geomagnetic disturbances.

The work is carried out at the financial support of RFFI, grant N 95-05-14329.

V.M. Uritsky, and M.I. Pudovkin (St.Petersburg University, St.Petersburg, Petrodvorets, 198904, Russia)

Long-period variations of the geomagnetic AE-index characterized by 1/f -like power spectrum (where f is a frequency) with spectral are studied. Basing on the analysis of experimental data there is shown that Bz-component of IMF and velocity of solar wind plasma are not sufficient factors for explaining these behaviour of AE-index and connected with them 1/f fluctuations of geomagnetic intensity. The effect of self-organized criticality (SOC) known from the theory of nonlinear systems is proposed as an internal mechanism of generation of 1/f fluctuations in the magnetosphere. It is suggested that localized in space current instabilities developing in the magnetospheric tail at the initial substorm phase can be considered as the SOC avalanches - dynamic clusters, superposition of which leads to the 1/f fluctuations of macroscopic characteristics of the system. Using sandpile model of SOC, numerical modeling of space-localized and global disturbances of magnetospheric current layer is fulfilled. Qualitative conformity between disturbed dynamics of self-organized critical state of the model and the main phases of real magnetospheric substorm development is demonstrated.

E.E. Antonova (Skobeltsyn Institute of Nuclear Physics Moscow State University, 119899 Moscow)

The role of eastward ring current in the magnetospheric substorm dynamics is analyzed. Such current arises on the equatorial boundary of plasma sheet due to antiearthward directed plasma pressure gradient. It produces negative Bz magnetic field disturbances on geocentric distances larger then its position and positive at smaller distances. It is shown that eastward ring current can produce the dominant contribution to the growth phase daytime magnetopause motion to the Earth. Eastward ring current increase at the time of substorm growth phase lead to nighttime field line stretching. It also can modulate near tail westward current in such a way that eastward current growth lead to near tail westward current growth. Eastward and westward plasma sheet currents form the region of very low Bz component localized near midnight and Region 1 field-aligned currents equatorial boundary. The existence of very low Bz region can lead to the development of many plasma instabilities. So the introduction of eastward ring current in the substorm currents analysis can help to understand substorm beginning localization. The role of medium scale plasma turbulence in magnetospheric plasma dynamics including growth phase plasma sheet thinning and expansive phase thickening is also discussed.

N.L. Borodkova¹, A.G. Yahnin², L.M. Zelenyi¹, Yu.I. Galperin¹, E.Yu. Budnick¹, V.N. Lutsenko¹, J. Hanasz³, R.A. Kovrazhkin¹, S.A. Romanov¹, V.A. Sergeev⁴, J.-A. Sauvaud⁵, Yu.I. Yermolaev¹

¹ Space Research Institute, Moscow, Russia

² Polar Geophysical Institute, Apatity, Russia

³ Spase Research Centre, R.A.S., Torun, Poland

⁴ Institute of Physics, University of St-Petersburg, Russia

⁵ CESR, Toulouse, France

Substorm dynamics was examined using plasma and magnetic field measurements onboard INTERBALL-1 and -2, GEOTAIL, LANL and WIND satellites, as well as ground based data. The main substorm developed under strongly negative IMF Bz conditions and consisted of the several intensifications. The first onset occured in the MLT sector that enveloped the positions of INTERBALL-1 and GEOTAIL satellites. The satellites located at different sides of plasma sheet observed plasma sheet thinning and tailward propagating plasmoid signatures. The only signature of another substorm intensification that occurred out of the MLT sector of INTERBALL-1 and GEOTAIL was global disruption of current sheet seen simultaneously in the both tail lobes. During the current disruption stage the appearance of low-energy ion (including O+) tailward flows and bidirectional electron fluxes in the tail is, likely, a manifestation of the plasma mantle approaching the satellite due to the decrease of pressure in the tail lobes. During the pass of INTERBALL-2 through the region of substorm-related auroral bulge the intensive AKR emissions were registered as well as the unusual spectra of precipitating energetic ions. High fluxes of O+ ions observed in the magnetosphere are the manifestation of the strong magnetosphere-ionosphere coupling during the substorm.

L.I. Vagina (Institute of Physics, University of St.Petersburg, St. Petersburg, Russia)

The change of structure magnetospheare is considered with excitation alfven waves in located force tube of a geomagnetic field first minutes after beginnings of substorms. Is shown, that the generation of alfven waves owes to be accompanied by excitation magnetocompression of fluctuations. The received results are used for interpretation of observations on the geostationary satellites, on which the significant amplitudes by component of pulsations, aligned to a geomagnetic field, are registered.

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

T. Mukai (ISAS, Japan)

S. Haaland (Dept of Physics, Univ. of Bergen, Norway)

D.G. Baishev (IKFIA, Yakutsk, Russia)

V.V. Klimenko (CMIS, Norilsk, Russia)

One of substorm features which importance for the substorm generation is widely disputed is the formation of the localized near-Earth neutral line (NENL). An expected result of the NENL formation is the tailward propagating (or expanding) region of closed field lines, or plasmoid. Two plasmoid events have been detected on November 22 and 27, 1995 by the Geotail satellite situated in the magnetotail at the distance of 25 and 20 Re, respectively. The plasmoids have been identified on the basis of magnetic field, plasma, and energetic particle measurements. The appearance of plasmoids was associated with substorms observed by numerous ground-based instruments. On November 27 the magnetic and plasma signatures of plasmoid were observed simultaneously with auroral breakup, but they were delayed for ~1-2 minutes for event on November 22. The delay is interpreted as a result of tailward propagation of the plasmoid. In the two cases, the energetic particle flux enhancements have been observed by Geotail simultaneously with auroral breakups registered by all-sky TV cameras. The timing of the phenomena strongly support the concept of the NENL as the key element of substorm scenario.

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

R. Rasinkangas (Unirversity of Oulu, Finland)

H. Singer (Space Environment Laboratory, NOAA, Boulder USA)

Magnetic field variations measured by the CRRES at the nigth magnetosphere are studied to estimate the changes in the near-Earth cross-field current Jo during the substorm. The line current model have been used to simulate equivalent currents dJ, associated with differential magnetic field perturbations. We assume that the current dJ is restricted to the equatorial plane and have an arbitrary orientation. Analysis of the current perturbations shows that:

1). Initial current decrease (CD) was observed at r~ 5-6 RE.

2). Within the dipolarization region the multiple localized and transient CD occur. Individual CD has short time duration (~10-20s) and separation ~ 1 min. Both Earthward and tailward transient displacements of CD with v ~ 200-1000 km/s were observed.

3). Rapid increase of the current intensity and tailward displacement of the westward current dJW were observed at r~ 6-8 RE during the sudden increase of magnetic field stretching (during the 'EGP') prior to the local dipolarization.

4). Perturbation current had a significant radial component. Before (after) Tdip this component had tailward (Earthward) direction. This component may be a part of the large- scale region 1/region 2 current system or a part of the meandering neutral sheet current.

5). Dispersionless injections of the particles were observed when the dipolarization process has started at r~ 5-6 RE.

V.R Tagirov, A.G.Ivanov (Polar Geophysical Institute, Apatity, 184200, RUSSIA)

V.A. Arinin (Russian federal Nuclear Senter, Sarov, Nizhny Novgorod region, Russia)

D. G.Sibeck, C.-I. Meng (The John Hopkins University, APL, Laurel, Mariland, USA)

L.A. Frank (University of Iowa, Iowa Sity, USA)

We present two substorm onsets on December 9, 1996. A set of ground and satellite observations was collected for this case. The development of the two substorms was different. The first one started just above Loparskaya, where all-sky TV camera was located. Accoding to WIND satellite data it was most probably triggered by a northward turning of the Bz component and an increase the solar wind pressure about 8 minutes prior to the onset. Ground optical and magnetic data and Polar satellite data show that the onset covered a very limited area and lasted about 15 minutes without developing further to recovery phase. This onset can be considered as a pseudo break-up disturbance. Another onset took place about 1 hour 20 min later at 22.51 UT. This one didn't have any noticable external triggering factors. The IMF was stable and stronly southward, wind dinamic pressure didn't exhibit any changes also. But contrary to the first onset this one developed to a very substorm expanding from the region located slightly westward from Loparskaya to both sides from it widening and finally covering the whole oval.

N.P. Dmitrieva, N.V. Miroshnikova, A.G. Yahnin (Polar Geophysical Institute, Apatity, Russia)

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

T. Hansen, B. Holmeslet (both from: Auroral Observatory, Tromso, Norway)

Some time ago it has been found that the favourite condition for substorm electrojet expansion from auroral zone to polar cap latitudes is the existence of high-speed solar wind streams [1]. Latitude that the substorm expansion may reach depends on solar wind velocity. For two solar activity cycles (from 1954 till 1978) it has been found that, in agreement with occurrence of high-speed solar wind streams, maximal number of "polar cap" substorms was observed when solar activity fell down [2]. The reason why the substorm propagation to the pole is so sensitive to the solar wind velocity was not defined. To verify above-mentioned results we performed a new study using the magnetic data from station Nord, Greenland (Inv.Lat. = 80). We expanded the interval of observations of the "polar cap" substorms until 1994, i.e. for one and half of the next solar activity cycle. All earlier findings were confirmed for this interval as well. Several extraordinary large substorm expansions were studied in details using the magnetic data from stations situated close to the geomagnetic meridian of Nord (Tromso, Bjornoja, Hopen, Ny Alesund) and simultaneous particle measurements from low-altitude satellites. The satellite data taken close to maximal stage of the substorms show a huge enhancement of energetic particle flux (of 1-3 orders more than pre-substorm value) in extremely wide latitudinal range (~15-20 degrees). This suggests a strong acceleration process operating in the entire plasma sheet, from the near-Earth region to the far tail. The acceleration is likely related with a strong induction electric field generated by explosive current instability (reconnection?) in the current sheet. Expansion of substorms into the polar cap means that during high-speed solar wind streams the conditions for the current instability are satisfied in the far tail. Thus, one can expect that the enhanced current sheet exist during such intervals. Recent results (e.g. [3]) on close relationship between an increase of lobe magnetic field in the far magnetotail and solar wind plasma pressure, gives us a hint that this idea is correct.

[1] Sergeev V.A., A.G.Yahnin, N.P.Dmitrieva, Geomagnetism and Aeronomy, V.19, #6, 1121-1122, 1979 (in Russian).

[2] Dmitrieva N.P. and V.A.Sergeev. In: Magnetospheric studies, #3, 58-66, 1984 (in Russian).

[3] Fairfield D.H. and J.Jones, J. Geophys. Res., V.101, 7785-7791, 1996

L.L. Lazutin, L.P. Borovkov, V.R. Tagirov, T.V. Kozelova, I.A. Kornilov (Polar Geophysical Institute, Apatity, Russia)

A. Korth (Max-Planck-Institut fur Aeronomie, D-37191 Katlenburg-Lindau, Germany)

J. Stadsnes S. Ullaland (Department of Physics, University of Bergen, Allegt. 55, N-5007 Bergen Norway)

H. Singer (Space Environment Laboratory, NOAA, 325 Broadway, Boulder, CO 80303-3328, USA)

CRRES energetic electron and proton measurements and auroral TV observations at Loparskaya, Kola Peninsula, are analyzed during moderate isolated substorm at 20-21 UT, February 13, 1991. CRRES was at the apogee of orbit 494 in the outer radiation belt near the magnetic equator. CRRES footprint projection calculated using Tsyganenko magnetic field model was situated 4⁰ east of Loparskaya during the breakup. It is shown that injected energetic electrons have been accelerated at the same time with one of the auroral activations at the same latitude and approximately the same azimuthal extended region. The lack of enhanced electrons during other activations suggests that the acceleration region have a sharp equatorial boundary.

L. Lazutin, I.. Kornilov, G. Starkov, T. Kornilova, L. Borovkov, S. Chernouss (Polar Geophysical Institute, Apatity, Murmansk Region, 184200, Russia)

J. Stadsnes, J. Bjordal (Department of Physics, University of Bergen, Allegt. 55, N-5007 Bergen Norway)

Our report presents a comparison of the PIXIE X-ray image dynamics with development of the polar aurora over Kola Peninsula, registered by TV cameras during 4 hours of the strong magnetospheric disturbance from 17.00 to 21.00UT, February 9, 1997. During 4-hour interval of magnetospheric disturbances polar aurora and X-rays occupied globally the same auroral oval region. As a rule nortward and southward borders of the region occupied by the aurora and X-ray emission coincide, confirming an assumption, that energetic and low energy auroral electron are accelerated simultaneously and in the same location. Local differences are existing first of all in a duration of the emissions: X-ray enhanced bursts are as a rule shorter, they are observed only at the initial stage of the aurora intensifications. Active aurora has been present over Kola Peninsula nearly continuously, whereas X-ray enhancements were observed with interruptions. X-ray events were registered simultaneously with different types of breakups or intensifications, but on some occasions were absent even during “classical” breakup with northward expansion. It seems, that predominant is an intensity of the disturbance rather than a type of the auroral activity.

V.Y. Trakhtengerts (Institute of Applied Physics, 46 Ulyanov st., 603600 Nizhny Novgorod, Russia)

Energetic particle injections during magnetic storms lead to formation of asymmetric part of the ring current (RC) and of specific zones of field-aligned currents localized near the plasmapause and detached plasma regions which appear in process of the plasmasphere erosion. These field-aligned currents are due to energetic particle precipitation caused by wave-particle interactions. Together with induced currents of cold plasma, the currents of hot particles form 3D current system in the subauroral magnetosphere and ionosphere. The magnetospheric Hall conductivity plays an important role in formation of this system, leading to generation of the ionospheric northward electric field located at the ionospheric projection of RC. This electric field increases with growth of RC intensity and reaches the saturation value determined by the energy of RC ions and can explain the structure and value of the electric field observed in the polarisation jet. The 3D current system provides not only transfer of the electric charge but also mass transfer, accumulating cold plasma in two contact regions of RC with plasmasphere located in the morning side and in the eveningside bulge. Between these regions, in the night side, an impoverishment of the ionospheric plasma density takes place.