I.B. Ievenko, V.L. Khalipov, V.N. Alexeyev, A.E. Stepanov (Institute of Cosmophysical Research and Aeronomy, Yakutsk, Russia)

Study results of the subauroral luminosity dynamics and ionisation at heights of F2-layer on the ground-based photometric and ionospheric observation data at the Yakutsk meridian for Kp=3-5 are presented. The following features have been related:

1. At the beginning of prolonged magnetic activity (several hours) at latitudes of the brightening SAR-arc the increase of the F2 regular layer height and the decrease of the electron density in 2-4 times occured (SAID condition).

2. Under the repeated increase of activity (the expansion phase of the next substorm) in the aftermidnight sector the main trough polar edge is observed equatorward of the diffuse precipitation boundary and shifted with the velocity of 20-50 m/s to the sounding station zenith.

3. Results of complex measurements suggest that SAR-arc and sporadic ionization motion equatorward of the diffuse precipitation zone is caused by the penetration of the magnetospheric convection electric field into the plasmasphere.

V.A. Arinin (All-Russia Scientific Research Institute for Experimental Physics, Sarov, Nizhny Novgorod reg.)

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

Classical papers about triangulation of aurora (for example [1]) were aimed to solve two primal problems: determination of the height of aurora formations and their global geographical projection. These problems were successfully solved, it was confirmed by orbital photos and other data. The analysis of the methodology of processing of ground-based video information shows that 3D problem in essence was transformed to the one-dimensional. Sophistication of developed methods of correction of distortion factors (optical distortion, deviation of zenith, correction of polar orientation) and precision of the results delights until now: the complex 3D problem was solved on the 16-bit PDP-11 computer basis.

It is very strange, that the progress in computerization, which allows any scientist to use high-power computers, has not resulted in progress in the methodology of the auroral triangulation task. Authors try to fill this blank in this paper.

The problem of auroral triangulation consists from two independent ones: geometric normalization of video-data (2D) and the triangulation is (3D). It is offered for solution of the first problem to fill the image of camera field by the most bright stars. It is possible always, because the recording in various time of day or day of year allows to cover with any density of bright stars the all-sky image. Having a set of actual (distorted) and theoretical (astronomical) coordinates of the stars, it is possible to determine for each star the transformation vector, which transforms actual coordinates of any star to geographical coordinates of its image on predicted height of aurora. Considering the stars as nodes of a triangular Guro grid, it is possible to receive the painting function of Guro, which in our case normalizes initial video-data. After projection in accordance with the obtained vector fields of the auroral images, obtained from the different view points, we can receive their joint geographical projection. It reduces the problem of 3D triangulation to non-adequate problem of two-dimensional similarity. It is wellknown fact that human eyes easily manages with such problems: the most vivid example - volumetric perception of scenes. The authors assume, that the well organized interface (dynamic change of prospective height) and specific submission of data (in conditionally orthogonal colours) will allow anyone to determine with high precision such characteristics of aurora as altitude and the authentic information about its spatial structure.

[1] Kari U. Kaila "Tree-Dimensional Mapping of the Aurora from Digitized All-Sky Pictures"; technical report No.25, 1981.

V.G. Vorobjev, O.I. Yagodkina (Polar Geophysical Institute, Apatity, Russia)

D.G. Sibeck, K. Liou, C.-I. Meng (Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland)

T. Kornilova, I. Kornilov (Polar Geophysical Institute, Apatity, Russia)

M. Pudovkin, O. Kornilov (Institute of Physics, St.Petersburg State University, St.Petersburg, Petrodvorets, Russia)

An auroral substorm is a complex phenomenon that couldn't be placed in the framework of a simple scheme. With the help of new devices and methods of auroral dynamics investigation it has been shown that substorms may have some specific features and even fundamental differences.

The analysis of TV auroral data we have done, reveals that well-known scheme of poleward expansion proceeded by the jumped formation of new arcs into more polar latitudes is not the only possible. We observed another type of a poleward auroral expansion during breakup. In the course of the second type breakup poleward expansion occurred not as leaps of arcs to the pole, but as spreading of shining auroral patched-shape region in different directions. This region may have irregular structure consisting of patches or arc fragments having no definite orientation. Both types of poleward expansion were observed during isolated substorms as well as in the course of double breakups. During double breakups the southern one could be the first or second type of expansion, but the northern one is only the first type.

The structure of poleward expansion region (system of quasi-parallel arcs leaped to the pole for the first type breakups and spreading in different direction patched-shape region during the second type breakups) allowed us to suggest that the first type breakups are associated with the reconnection processes and the second type connected with another mechanism of substorm onset in the inner magnetosphere.

T. Kornilova, I. Kornilov (Polar Geophysical Institute, Apatity, Russia)

M. Pudovkin, O. Kornilov (Institute of Physics, St.Petersburg State University, St.Petersburg, Petrodvorets, Russia)

Auroral arcs dynamics during double breakups (DB) representing simultaneous poleward expansion in two regions spaced in latitude in the same longitudinal sector have been considered. It is found that usually the northern breakup emerges earlier than southern one and distance between them depends on the magnetic activity. For strong substorms this distance is of order of 8 degrees in latitude and for the weak ones is about 4 degrees.

It is shown that contact of equatorward moving arcs of the northern breakup and poleward spreading arcs of the southern one can lead to three different consequences: to damping one of the breakups (northern or southern), to damping both of them or to the development of large-scale breakup occupying the whole field of view of TV all sky camera.

Changes of the velocities of equatorward drifting arcs and poleward moving auroras in the ionosphere before and after contacts of DB are investigated. It is shown that equatorward moving arcs velocities of the northern breakup decrease before the contact and increase after it, while the same velocities of southern breakup, on the contrary, decrease after the contact. Poleward expansion velocities of both north and south breakups increase before the moment of the contact and decrease after it. Corresponding changes of the velocities are interpreted in the light of the magnetospheric models with two neutral lines during the substorm active phase.

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

Vast amount of different methods for the image processing and improvement have been developed during last decades (robotics, machine vision, remote sensing satellite data, radars, sonars and so on). Some of them (and really very few) were applied for the auroral TV data processing. Examples presented demonstrate significant improvement of TV frames and keograms especially when initial data happened to be very poor (some disadvantages of TV camera electronics, operator's mistakes, bad natural conditions like fog, clouds, city lights background and so on). Sometimes it is even possible to reveal image details invisible by the ordinary processing. Using these methods, some interesting aurora features have been found in TV data. Among them one can see very weak pulsations during breakup preliminary phase, separation of space and time variations in pulsating patches, differences in the high frequency pulsating component behavior for the northern and southern stations, etc.

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

O.I. Kornilov (Institute of Physics, University of St-Petersburg, Russia)

Auroral forms usually demonstrate very close correlation in the east-west direction (long E-W oriented arcs, spreading pulsating fragments, eastward drifting omega bands and so on). Using all-sky TV data, different correlations characteristics of aurora have been studied for the northern and southern parts of TV camera field of view (about 800 km at 200 km height, that means about 2-3 Re at the magnetosphere equator). It was noticed that a typical feature of auroral activity is a weak, but quite visible correlation of luminosity between northern and southern parts of the auroral oval. During strong magnetic disturbances lasting for several hours repeated in 30-50 minutes sequences of double breakups sometimes can be observed. It was shown that close interaction of auroras with two types of correlation in the region of the northern and southern breakups exists. At the time scales of about breakups repetition period intensity maximum of the northern breakup in average for 5 minutes leads the one of southern breakup. At the shorter time scale of the order of 100 seconds small and fast changes of luminosity in the region of the northern breakup stably lead ones of the southern breakup for about 2-5 seconds. That type of correlation N-S with characteristic time delays in the range of a few seconds have been also found for some other aurora activisations (breakup at the north and pulsations at the south, pulsations and diffuse aurora, fast and slow pulsations). Because it is very difficult to explain so fast information exchange in the outer magnetosphere, ionospheric correlation mechanism can be supposed.

B.V. Kozelov (Polar Geophysical Institute, Apatity, Russia)

During the last two decades the fractal geometry has become a powerful approach to the different physical problems. It is also found to be useful in image processing applications. A numerical quantity that characterizes the auroral structure would be important for auroral investigations. We try to obtain the quantity on the base of box-counting dimension. In this paper we present application of box-counting procedure to several long sets of digitized TV images. Here we used the TV observation data obtained in Loparskaya and Lovozero stations. Discussion of some results is also presented.

V. Safargaleev, S. Osipenko, A. Vasil'ev (Polar Geophysical Institute, Apatity, Russia)

Several intervals of TV observations of the auroral arcs drifting periodically across the pre-midnight sector of the double oval are examined together with magnetic measurements on the ground. Each interval includes four or five passes of the arc through the oval toward either pole or equatorial boundary where the arc fades. The pass time is 60-90 s. The arc velocity is 0,5-1 km/s at ionospheric altitude whereas the oval boundaries move rather slowly. The sequence of the passes coincided with a Pi2 signature at a nearby ground magnetometer, so that every pass may be associated with the magnetic disturbance of approximately the same duration. We discuss a specific type of MHD-disturbances in the magnetotail plasmasheet as a reason for those auroras. We obtained a dispersion equation for the waves propagating inside the region of gradual increase of the plasma pressure under the effective "gravity" force due to the magnetic field line curvature. These waves may propagate both parallel and perpendicular to the magnetic field forming a specific resonant Alfven wave and cause the electron precipitation because of the large compressional component.

V.N. Alexeyev, I.B. Ievenko (Institute of Cosmophysical Research and Aeronomy, Yakutsk, Russia)

The occurrence rate of the subauroral red arcs (SAR-arcs) has been Studied, using photometric observations at the Maimaga station (56.5 N, 200 E, geomagnetic coordinates) at the Yakutsk meridian in the period 1988-1998. Observations have been carried out in winter-spring periods in moonless nights under favourable atmospheric conditions. 109 events of the occurrence of SAR-arcs (557 hours) during 239 observation nights (2031 hours) were registered. The occurrence rate of SAR-arcs for each specific year was determined as a ratio of the total registration time of SAR-arcs to the summary observation time in hours per year. It is obtained that the occurrence rate of SAR-arcs is associated with the phases of the 22 nd solar cycle. They occur most commonly at the solar activity maximum (by the number of sunspots) and at the decay phase (~40%) and rarer - in the solar activity minimum (~15%). Dates and intervals of photometric observations of the SAR- arcs for 1988-1998 are presented.

I.B. Ievenko, V.N. Alexeyev (Institute of Cosmophysical Research and Aeronomy, Yakutsk, Russia)

Several events of 557.7 nm (427.8 nm) emission intensification in the form of a narrow band at SAR- arc latitudes were registered with the photometers at the Yakutsk meridian (50-60 N; 200 E; geomagnetic coordinates) for 1988- 1998. This phenomenon was observed in the evening MLT sector on March 5, 1989 (during 50 min), on March 9, 1994 (40 min), on March 10, 1994 (20 min) and on January 14, 1999 (3 hours) when the SAR- arcs were in the vicinity of the magnetic zenith of the observation station. In all the cases, a width of the green band (arc) was less by a factor of 3-4 than the SAR- arc width. In the event on January 14, 1999 the band had 2 and 3 maxima of the intensity in the latitudinal section. In each of considered cases the 557.7 nm emission intensity in the band was different and varied in time (100-1000 R). In the event on March 10, 1994 the SAR- arc and the green band appeared simultaneously prior to the intensification onset of the magnetic and auroral activities. The 557.7 nm emission intensity in the band was as much as 8000 R followed by an increase of the red line intensity to 1000 R. Once the green band disappeared, the SAR- arc was registered during ~10 min and its intensity was decreased.

The detail analysis of experimental data allowed to assume, that the appearance cases of the green band at SAR- arc latitudes are caused by the energetic particle precipitation. The process of particle precipitation is developed in the region of the radial density gradient of cold plasma inside the plasmasphere which is mapped by the SAR- arc. This process is also accompanied by the heating of the plasmaspheric electrons and it is the additional source of the SAR- arc.