1 Institute of Cosmophysical Research and Aeronomy, Yakutsk, Russia

2 Kyushu University 33, Hakozaki, Fukuoka, 812-81 Japan

V.S.Ismagilov and V.R.Tagirov (Polar Geophysical Institute, Apatity, Murmansk region, 184200, Russia)

Fast and dynamic processes in auroral phenomena occupies a particular place in investigation of auroral physics. First of all it concerns pulsating auroras and active rayed structures in all variability of thier displays. Characteristic times of their generation and variations are measured by tenth and hundredth of seconds and need computer analysis of relatively long time intervals of auroral TV data with high temporal resolution. It requiers the development of a special software for massive analysis of video data which is calculated in thousands and tens of thousands of TV frames. The approach to this problem is concluded mainly in obtaining of uniformity of initial data using methods commonly accepted in image processing and in the form of presentation of results. This methods allow to separate temporal and spatial variations of intensity in auroral displays. The examples of results of massive processing are presented in the paper.

Obviously the visible aurorae are the elements of powerful current disturbances in the magnetosphere and auroral ionosphere. Hence their characteristics are formed to a considerable extent by the state of ionospheric link.

By the observations of many years in Tixie Bay and Norilsk Station it is shown: 1) the average brightness of discrete aurorae decreases as the time interval after the sunset at ionospheric altitudes increases; this effect is confirmed by the comparative analysis of the artificial rays brightness in the experiments "Zarnitsa-1" and "Zarnitsa-2", which were carried out at the different dip of the Sun under horizon; 2) the more bright auroral rays are observed after the more power corpuscular precipitation; 3) after sunrise in the magnetoconjugate ionosphere the clear increase of the brightnes s of discrete auroral forms (0.5-0.9 kR) is observed; around the sunset in the magnetoconjugate ionosphere the response in auroral brightness is inverse; 4) the sudden ionospheric disturbances (SID) observed in the sunlit magnetoconjugate ionosphere after the solar flares cause the jump of average brightness of discrete auroral forms at the side of geomagnetic field tube placed in the night hem isphere; 5) around the moment of near earthquake (from -7 hours to +22 hours) of the magnitude M<5 a decrease of average brightness of discrete aurorae is observed.

This results are interpreted from the single point of view as the auroral brightness responses to variations of ionospheric conductivity in the local or magnetoconjugate region. The following sequence of the interdependent processes is considered: 1) the increase (or decrease) of ionospheric conductivity (sunrise-sunset, variations of the intensity of corpuscular precipitation, SID, ionospheric depletions over the earthquake epicenters et al.); 2) the intensification (or attenuation) of the auroral current system; 3) the increase (or decrease) of the localized regions number of anomalous resistivity and double potential layers at the branches of field-aligned currents; 4) the intensification (or attenuation) of electron acceleration mechanisms at the branches of forward and inverse field-aligned currents; 5) the increase (of decrease) of the intensity of discrete electron intrusions into the local and magnetoconjugate auroral ionosphere.

N.N.Shefov, V.M.Ponomarev (Institute of Atmospheric Physics, Moscow)

One can define a variety of auroral phenomena. A lot of processes in magnetosphere-ionosphere plasma lead to various and dynamic auroral displays. Investigation of this processes requires to separate temporal and spatial variations of intensity in auroral displays. For this we need a numerical characteristic of auroral structure. Fractal geometry is useful approach to this problem. A modified box-counting method has been used to obtain the fractal dimension D of image boundaries for different auroral forms. It is found that D value mainly lied in region from 1.1 to 1.4 and tend to be higher for more developed auroral displays. Dependence of D on intensity threshold and image quality is discussed. We conclude that this fractal dimension may be used to characterize numerically the local auroral structure.

V.A.Arinin (Russian Federal Nuclear Centre, Sarov, 607200, Russia)

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

The interaction of magnetic cloud with the Earth's magnetosphere on the basis of TV auroral observations, magnetic ground-based and IMF data and plasma parameters of the solar wind was studied for the time interval from 04.17 to 10.30 UT on 14.01.1988. Auroral TV observations were carried out in Frants-Joseph Land (Heiss Island) and covered the whole dayside sector corresponding to the event. Auroral forms represented very active rayed forms travelling mostly in azimuth direction with velocities about several kilometres per second. The polar plots of auroral motion showed that they moved following to "inverse" twin-cell convection pattern with sunward flow over the pole. We divided the whole interval of auroral observations into three regimes depending on the characteristics of auroral motion and solar wind and IMF parameters. The IMF Bz-component during the whole interval was very high exceeding 18 nT whereas By-component changed the sign at about 1.5 h later the local magnetic noon at the point of auroral observations, By was slightly positive.The first regime was characterised by a very steep increase in solar wind dynamic pressure. The second regime differed by much less dynamic pressure values and pronounced sunward flow motion of auroral forms. The third regime was characterised by change of auroral forms velocity vector to the eastward direction. The possible mechanisms of transient events generation for all three regimes are discussed.

With the using of TV photometers and direct TV frames digitizing space correlations in the different types of pulsating aurora were investigated. FFT spectra revealed that even spaciously close pulsations can have rather different periods. Two dimensional representation of crosscorrelation functions have shown very broad velocities range of pulsations motions in E-W and N-S directions. Data from the narrow field TV camera have demonstrated the presence of nonpulsating core in some auroral pulsations and moving pulsations have no influence on it. No direct evidence of the presence in pulsations motions the drift speed of high energy electrons responsible for the pulsating aurora were detected.