Physics of auroral phenomena : proceedings of the 39th annual seminar, Apatity, 29 February-4 March, 2016 / [ed. board: N. V. Semenova, A. G. Yahnin]. - Апатиты : Издательство Кольского научного центра РАН, 2016. - 167 с. : ил., табл.

“Physics o f Auroral Phenom ena”, Proc. XXXIX Annual Sem inar, A patity, pp. 36-39, 2 0 1 6 D Polar Geophysical Institute, 2016 Polar Geophysical Institute SC-ASSOCIATED VLF-EMISSIONS AT TWO CLOSELY SPACED AURORAL STATIONS: CASE STUDY DECEMBER 23, 2014 N.G. K leim enova12, l.A . K o rn ilo v , J. M anninen4, Yu.V . Fedorenko3, L .I. G rom o v a5 1Schm idt Institute o f Physics o f the Earth, Moscow , Russia 2Space Research Institute, Moscow , Russia ' P o la r Geophysical Institute, Apatity, Russia 4Sodankyla Geophysical Observatory, F inland 5Pushkov Institute o f Terrestrial Magnetism , Ionosphere and Radio Wave P ropaga tion , M o scow , R u ssia e-mail: kleimen@ ifz.ru Abstract. The SC effects in VLF emissions were studied basing on the simultaneous VLF observations at Finnish station Kannuslehto (KAN) and Russian station Lovozero (LOZ) located at the same geomagnetic latitude but separated by -400 km in the longitude. The considered SC has happened on December 23, 2014 at 11.14 UT under northward IMF. Thus, geomagnetic and VLF effects in the magnetosphere were caused most o f the enhancement of the solar wind dynamic pressure. There was the daytime SC associated VLF burst (VLFsc) and a succeeding strong VLF hiss, which started several minutes after SC. A sharp particle flux enhancement (typical for SC) was observed at first by THEMIS В (ThB) satellite, located in front of the magnetosphere at X=~50 Re and Y=~20 Re, about 10 min before the SC impulse observed on the ground. Increasing electron and ion fluxes were observed by ThA. ThD, and ThE in the evening sector (at X=—7 Re, Y=~10 Re). These satellites recorded strong pressure depletion between the VLFsc burst and the subsequent VLF hiss onset. The VLFsc burst represented the composition of a high-frequency (-2-5 kHz) left-hand polarized part and a low-frequency (-0.5-1.5 kHz) right-hand polarized part. According to the KAN data, the VLF signals arrived from the meridian (North-South) direction. However, the LOZ 3-component receiver allows to estimate the signal arriving azimuth. It was found that the VLF high-frequency part arrived from the South, but the VLF low-frequency part arrived mainly from overhead. The plasmapause location estimated by RBSP (A and B) satellites showed that KAN and LOZ were mapped outside of the plasmapause. We suppose that the 2-5 kHz hiss burst was originated inside of the plasmasphere and the 0.5-1.5 kHz hiss -outside of it. In spite of the similarity of general spectrogram and polarization at KAN and LOZ, the small differences have been found, and the VLF signals arrived to these stations from different direction due to KAN location closer to the wave exit point than LOZ. -----■------------ { ---- T --— — X ‘ ; f V . 1 v t L*. “V 1 ч _______ n / f i i \X ■ > Kannuslehto VTt-ovozero V . j \ | L —O — t *■------ qh *—— , 4 pS L - 4 . 5 - ^ - Ч 'ч Ч Л I - ^ t « * . ' т Щ ш к • \ 2 ______________L --$ S g B p — й — v — * • • 1. Introduction It is well known that a sudden commencement (SC) is caused by interplanetary shock and has been interpreted in terms of a compression of the magnetosphere [e.g., Nishida, 1978; Shinbori et al ., 2003; Yu et al., 2015] resulting electron cyclotron VLF wave generation. Here the SC effects in VLF waves were studied basing on simultaneous VLF observations at Kannuslehto (KAN) in Finland and Lovozero (LOZ) in Russia. They are located at the same geomagnetic latitude but separated by -400 km in the longitude (Fig. 1). The studied SC event has occurred on 23 Dec 2014 at 11.14 UT under northward IMF (Fig. 2), i.e. there was no new particle input from the solar wind into the magnetosphere. But the previous day was disturbed and Kp was 5. The plasmapause location estimated by the RBSP (A and B) satellite data showed that during the event, KAN and LOZ (the asterisk in Fig. 3) were mapped outside the plasmapause (Fig. 3) due to strong magnetic activity during previous day. Figure 1. The map of the station location Figure 2. IMF and solar wind data 14 С -GO 36