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

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

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

Besides the Pi2 and PiB substorm related geomagnetic pulsations there is a rich concert of irregular high latitude long period (3-15 min) pulsations at different longitudinal sectors of magnetosphere corresponding to substorm development. The growth phase of substorm leads to the increase of ipcl geomagnetic activity near dayside polar cusp/cap. These pulsations may suddenly disappear in time of night side substorm onset. This effect in the North hemisphere is stronger when the IMF By is negative and in the South hemisphere - when the IMF By is positive. The expansion phase of substorm is accompanied by latitude located bursts of ipcl-type (Pi3 ?) pulsations. During the recovery phase there is a new ipcl cusp/cap pulsations activisation. The relationship between field aligned currents and ipcl pulsations generation is considered.

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

V.A. Sergeev, M.V. Kubyshkina (Institute of Physics, University of St-Petersburg, Russia)

N.L. Borodkova (Space Research Institute of RAS, Moscow, Russia)

T. Bosinger (Department of Physical Science, University of Oulu, Finland)

T.I. Pulkkinen (Finnish Meteorological Institute, Helsinki, Finland)

D.G. Sibeck (Applied Physics Laboratory, Johns Hopkins University, Laurel, USA)

V. Angelopoulos (Space Sciences Laboratory, University of California, Berkeley, USA)

S.Kokubun (STEL, Nagoya University, Toyakawa, Japan)

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

The substorm commencing at 2053 UT on Dec 15, 1996 has been investigated in many details using the data from satellites Polar, Geotail, Interball-1 together with a number of ground based instruments. Clear auroral breakup has been detected by Polar UVI and by several auroral TV cameras situated on Kola Peninsula and Scandinavia. Simultaneously several magnetic stations recorded the onset of magnetic bay and Pi2/PiB pulsations. Interball-1 situated in the tail lobe at X=-10 Re registered sharp decrease of the magnetic field Bx component (current disruption), and a little bit later Geotail detected the fast tailward plasma and energetic particle flow and bipolar variation of the magnetic field Bz component (the plasmoid) near the neutral sheet at X=-23 Re. Magnetic measurements from the three satellites were used to modify the T89 magnetospheric magnetic field model. The modified model suggests the existence of very thin current sheet at X=-(9-15) Re just prior the breakup. Mapping of the brightening auroral arc onto the magnetotail gave its core at X=-(10-12) Re, that is in the region of the thin current sheet and current disruption. Estimate of the NENL location made on the basis of the plasmoid characteristics also gave the same distance.

The observed sequence of magnetotail phenomena agrees with the substorm onset scenario in which the current disruption occurs in the near-Earth plasma sheet in close relation to reconnection process and generation of tailward moving plasmoid.

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

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

The dynamical variability of particle fluxes, associated with substorm processes, is the subject of intensive study of many years. A key feature of substorm 'dispersionless' injections is that the particle fluxes increase nearly simultaneously over a very broad range of energies (including both electrons and ions). Lezniak and Winckler (1970) showed the correlation of increases in the electron fluxes with increases of local magnetic field. Moore et al (1981) proposed that the injections correspond to some kind of compressional wave that propagates Earthward and may be associated with westward current of perturbation. However, the increase in the magnetic field strength (dipolarization) after substorm onset may indicate, that the total westward current intensity decreases suddenly (i.e. current disruption) or the eastward current of perturbation appears. We investigated changes in the magnetospheric cross-field current during the proton and electron injections on the CRRES spacecraft. The differential vectors of the magnetic field have been used to identify the current perturbations. The line current model have been used to interpret equivalent currents, associated with these magnetic field perturbations. Analysis of current perturbations showed that the current of perturbation in the injection front may be directed both westward and eastward depending on the spacecraft position in respect to the site of active region.

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

P. Eglitis, H. Opgenoorth (Swedish Institute of Space Physics, Uppsala Division, Uppsala)

M.V.Uspensky (Murmansk State Technical University, Murmansk)

T. Pulkkinen, R.J.Pellinen (Finnish Meteorological Institute, Helsinki)

During the afternoon and evening of November 17, 1996, 1530-1830 UT, when the geomagnetic conditions are rather quiet, the Finland CUTLASS radar observed a thin persistence echo strip which was gradually moved equatorward as time progresses from afternoon to late evening time. Similar echo signatures during weak to moderate magnetic activity have been observed during other afternoon-evening events. A comparison of the CUTLASS radar data for November 17, 1996 with the AL-dependent model of the auroral boundaries shows that the echoes locate and follow reasonable well the equatorward edge of the diffuse luminosity belt. The pre-substorm magnetic activity in the data collection area (1530-1830 UT, 1800-2100 MLT) was around 50-70 nT, in the early morning sector in Eastern Siberia 50-60 nT and in the global AL-index around 80-100 nT. It is interesting to note the Finland CUTLASS radar can monitor the equatorward edge of the diffuse luminosity belt during a period the ground-based optical observations are not possible due to the sunlit conditions. The Finnish digital all sky camera in Muonio detected the edge of the diffuse luminosity and a faint auroral arc only after 1908 and 1912 UT respectively. We found that the auroral boundaries and the Muonio optical data are in reasonable good agreement with each other.

It seems that the Finland CUTLASS F-layer echoes and the start of their gradual equatorward motion from the poleward edge of the auroral oval is the first indicator of the substorm growth phase development. These signatures appeared at least 20 minutes earlier than similar information derived from the ground-based geomagnetic and optical data. The mean velocity of the F-echo motion allows us estimate the growth-phase electric field within of the auroral oval to be of the order of 25 mV/m. This is in accordance with other measurements.

V.R. Tagirov (Polar Geophysical Institute, Apatity, Russia)

V.A. Arinin (Russian Federal Nuclear Center, Sarov, Russia)

K. Liou, C.-I. Meng, D. Sibeck (John Hopkins University, Applied Physics Laboratory, Laurel, MD 20723, USA)

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

Statistical relation of the three hour Kp geomagnetic index to hourly solar wind data (magnetic field, dynamic pressure, bulk flow velocity, etc.) has been analyzed. Data for 28 years from 1963 to 1991 have been used. The dependence of Kp on IMF B_z appeared to have a deep minimum under B_z ~ 0, Kp growing with both positive and negative IMF B_z values almost symmetrically. Study of Kp relation to other geophysical parameters has revealed the solar wind velocity and proton number density to be the factors causing the Kp growth under positive IMF B_z.

M.G.Gelberg, S.Z.Kershengolz, S.V.Sharaeva (Institute of Cosmophysical Research and Aeronomy, Yakutsk, Russia)

The influence of four solar sources: suddenly disappearing filaments (SDF), coronal holes (CH), heliospheric current sheet (HCS) and solar flares (sf) on the development of four types of long (>10 h) auroral disturbances (HILDCAA) are investigated for 56 events from [1].

It is shown that SDF-streams create the second type HILDCAA with the bay-shape disturbances of AL and AU indices of a duration more than 3 hours and the deep modulation (about 1) of AE-index. It is stated that for CH- and HCS-stream classes the first type HILDCAA with the great number of short-period (<10 min) bursts of large amplitude in AU- and AL-indices and small modulation depth of hourly AE-indices must predominate. Sf-streams cause the third type HILDCAA which are a train of substorms of 0,5-3 hours duration. It is found that in interaction of interplanetary plasma streams from a few solar sources, the total intermixing of streams near the Earth orbit did not occur. Geoefficiency of one of the streams dominates. At the duration of event more than 40 hours, a change of domination of stream geoefficiency from the different sources is observed. Then, in the auroral zone, one type of HILDCAA is replaced by the other without the fading of geomagnetic disturbance. It is found that if SDF-stream interacted with the streams from other solar sources, then in auroral zone the second type HILDCAA was developed. Sf-streams probably dominate less in the streams of mixed classes: from 25 events with sf-streams the third type of HILDCAA was found in 8 cases, whereas a relative part of the third type HILDCAA was ~0,4 from their total number.

The fourth type of HILDCAA coinciding with the stationary convection periods is observed only one time, 16.08.78, when the Earth crossed the SDF+CH-streams. But even in this case the features of the first and second types of HILDCAA were observed. The relative appearance frequency of the fourth type HILDCAA is ~0,2, and their absence in this event is an evidence of the non-completeness of classification of interplanetary plasma streams and their solar sources from [1].

[1] K.G. Ivanov Solar sources of interplanetary plasma streams at the Earth`s orbit // Geomagnetism and Aeronomy International. 1998. V.1. #1. P.1.

M.G. Gelberg, S.Z. Kershengolz, S.V. Sharaeva (Institute of Cosmophysical Research and Aeronomy, Yakutsk, Russia)

The possibility to classify the long auroral disturbances (HILDCAA) into four types by using minute values of auroral indices is shown. The first type of HILDCAA is different from the remaining ones by the large number of short-period (10 min) bursts in AL and AU indices and by small modulation depth of AE-index. The second type is a train of bay-shape disturbances in AL and AU. A duration of each bay is more than 3 hours and the modulation depth of AE is about 1. The third type is a train of substorms of 0,5-3 hours duration developed against the background of the disturbed DP-2 current system. The fourth type corresponds to stationary convection periods earlier described by V.A.Sergeev et al.

The variations of HILDCAA appearence frequency of each type from season to season and in a solar activity cycle are investigated after the data of auroral indices for the period of 1978-1993. It is found that a probability of appearence of the first type HILDCAA has two maxima in spring and in autumn, and minima- in summer and in winter. The distribution of the appearence frequency of the fourth type HILDCAA has a wide maximum in the period from April to August, and for the remaining months of the year it is equal to 1/4 of maximum one. In seasonal distributions for the second and third types a clear minimum in June and growth of the probability of HILDCAA appearence in winter months are found.

The analysis of distribution of the appearence probability of different type disturbances of HILDCAA in a solar activity cycle showed that appearence frequency of the first and fourth types was maximum in years of maximum solar activity, and for the second and third types- at the minimum solar activity.

The above results are interpreted in the context of seasonal position of the Earth relative to the equator of the Sun and 11-year variations of the sources of solar wind disturbances of different types.

L.P. Shadrina, V.G. Vasilyeva (Institute of Cosmophysical Reseach and Aeronomy, Yakutsk, Russia)

The main characteristics of observed global auroral dynamics correspond to the classical scheme of an auroral substorm series but not for all storm conditions. The energy entrance estimation by means of statistical parameters (modulus index, average energy E) gives the opportunity for comparison of two energy transferring ways from solar wind to inner magnetosphere.

It means that it is possible to get some more information due to fractal features of statistics turned out earlier for geomagnetic activity. There was made analisys of the role of time module t in those two different storm conditions. The relationship between two parameters 1/t ~ E, reflecting usual injection intensification is also discussed.

В.А. Величко, Р.Н. Бороев, Д.Г. Баишев

При переходе от магнитоспокойных к возмущенным условиям после начала предварительной фазы суббурь по данным долготной цепочки низкоширотных станций обнаружено:

1) за несколько десятков минут до начала взрывной фазы суббури появляются две-три микробухты в Н- и D-компонентах длительностью несколько минут и максимальной амплитудой, достигающей единицы нТл;

2) полярность D-компоненты первых двух микробухт к западу от центра ожидаемого очага суббури - положительная, к востоку - отрицательная.

3) в восьми из рассматриваемых десяти суббурь для первых микробухт к западу от центра суббури максимальное значение D-компоненты опережает на несколько минут появления максимума в Н-компоненте, к востоку от центра максимальное значение в Н-компоненте наблюдается на несколько минут раньше, чем максимум в D.

Дрейф первых микробухт в азимутальном направлении, наблюдаемый за несколько десятков минут до начала взрывной фазы суббури, вероятно вызван движением максимумов токов зоны 2 к центру будущего очага суббури.

В.А. Величко, Р.Н. Бороев, Д.Г. Баишев

За несколько минут до начала взрывной фазы суббурь в разных долготных секторах на средних и низких широтах обнаружены характерные изменения в вариациях D-компоненты геомагнитного поля: западнее центра ожидаемого очага появляется отрицательная бухта, восточнее - положительная. Положение центра семи рассмотренных суббурь в момент взрывной фазы установлено по магнитограммам авроральных и среднеширотных станций. Восстановлены направления системы продольных токов относительно центра будущего очага суббури. Оценки долготных масштабов втекающего на западе и вытекающего на востоке тока варьируют от нескольких градусов до нескольких десятков градусов.

Показано, что система продольных токов возникала за несколько минут до начала взрывной фазы. В начале взрыва происходила смена направлений токов на противоположные и наблюдалось существенное увеличение масштабов токовой системы по долготе.