V. H. Guineva

Substorm observations by THEMIS D and ground-based observations by MAIN camera system in Apatity - a case study

In this work we studied the development of a substorm during the geomagnetic storm on 23 December 2014 using data of THEMIS D (THD) satellite, ground based magnetic field measurements and auroras observations by the Multiscale Aurora Imaging Network (MAIN) in Apatity. Solar wind and interplanetary magnetic field parameters were taken from the OMNI data base. THD was located at ~ 7Re from 18:30 to 19:30 UT in the time interval 23-24 December 2014 and the projection of its orbit crossed Kola Peninsula in this time. A substorm was observed over Apatity from 19:19:50 UT on 24 December 2014. A comparative analysis between ground based and satellite data was carried out. High energy electrons (1-10 keV) injections and reduction of the less energetic electrons flux (~100 eV) were observed during the substorm. Particles density reduction was found at the time about the auroras intensifications. Plasma fast flows were identified during the consecutive auroras intensifications. The time delay between the beginning of the different parameters disturbances registered by THD and the ground based observed ones is about 1.0 ÷ 1.5 min.

Investigation of Halley's Comet dust size distribution by Vega-2 interplanetary station visual spectra analysis

Spectra in the visible region measured on board the Vega-2 station are analyzed to obtain the solar spectrum continuum reflected by the dust particles in the Halley comet coma. It is suggested to determine the continuum level for every individual spectrum. By the time of Vega encounter, the concentration and distribution of particles around the comet has changed. This resulted in a different spectral indices for spectra measured in different time. The cumulative size index has been calculated for each specific spectrum by linear regression on the basis of a random number of dust points. Eleven dust continuum wavelengths are selected. The spectral index shows the mean particle size in the line of sight column around the nucleus (values calculated for 1019 spectra are in the interval of 2.85 - 3.48). Its change with the radial distance to the nucleus is discussed. The continuum spectra are calculated with the obtained values of the spectral index and are normalized to the real spectra on the minimum of interval of +/- 15 pixels in relation to the specific dust intensity, with the help of a linear regression. The continuum spectrum follows well the course of the specific Halleys comet spectrum.