Physics of auroral phenomena : proceedings of the 40th annual seminar, Apatity, 13-17 March, 2017 / [ed. board: N. V. Semenova, A. G. Yahnin]. - Апатиты : Издательство Кольского научного центра РАН, 2017. - 143 с. : ил., табл.

Polar © Polar Geonhvsical Institute. 2017 Institute “Physics o f Auroral Phenomena”, Proc. XL Annual Seminar, Apatity, pp. 100-103, 2017 fn/UU Geophysical GEOMAGNETIC AND IONOSPHERE TEC RESPONSE TO THE ABRUPT INCREASE OF SOLAR WIND DENSITY V.B. Belakhovsky1, V.A. Pilipenko2, Ya.A. Sakharov3, S.N. Samsonov4 1 Institute o f Physics o f the Earth, Moscow 2Geophysical Center, Moscow 3Polar Geophysical Institute, Apatity 4Institute o f Cosmophysical Research and Aeronomy, Yakutsk Abstract. We have examined multi-instrument observations of the geomagnetic and ionospheric response to the interplanetary shock on 24 January 2012. World-wide ground magnetometer array detected shock-induced sudden commencement (SC) with preliminary and main impulses throughout dayside sector, and substorm triggering in the nighttime hours. Clear resonant transient Psc5 oscillations are independently generated on the morning and evening flanks, no signatures of theoretically predicted cavity mode excitation is found. A new effect found was a 30-40 % positive pulse of the ionospheric total electron content caused by SC as determined from GPS receivers in the dawn sector and 10% pulse in the dusk sector. The VHF radar EISCAT in Tromso observed SC-associated increase of electron density in the bottom ionosphere (100-180 km). SC was accompanied by a burst o f cosmic noise absorption recorded along a latitudinal network of riometers in Scandinavia. A responsible mechanism of TEC modulation may be related to field-aligned plasma transport by Alfven pulse, which provides an additional plasma flow in the bottom ionosphere. 1. Introduction. An impact of interplanetary (IP) shock onto the magnetosphere, observed by ground magnetometers as storm sudden commencement (SC), is a convenient probing signal for the experimental study of the near-Earth space. During a relatively short time period (<10 min) a significant energy and momentum is pumped into the magnetosphere from the solar wind. Despite a seemingly simplicity of such impact, a complex of impulsive and quasi-periodic phenomena stimulated by IP shock in the ultra-low-frequency (ULF) band (time scales from few sec to tens of min.) turns out to be surprisingly large. An observed response to an IP shock or discontinuity may be rather complicated due to the nearly-simultaneous excitation of several transient processes. The IP shock is known to stimulate a global compression o f the magnetosphere [Araki, 1994], excitation of transient field-aligned current systems [Fujita et al., 2005], generation o f transient ULF waves in a wide band from Pci to Pc5-6 [Saito and Matsushita, 1967], triggering of VLF wave activity and enhancement of energetic electron precipitation [Gail et al., 1990], dayside aurora activation - “shock aurora” [Vorobiev et al, 2008]. Besides that, a SC pulse serves as an indicator of the onset o f a more intense solar wind driving and buffeting the magnetosphere. Though the basic physics of the related phenomena are qualitatively understood, some aspects of IP shock impact on the magnetosphere - ionosphere system has not been sufficiently established yet. Basing on the analysis o f ground magnetometer data, Araki (1994) suggested the phenomenological model o f SC, in which an observed disturbance is interpreted as the superposition of a stepwise compression of geomagnetic field (DL component) and bi-polar impulse, composed from a short preliminary impulse (PI) and following main impulse (MI). The nature o f a stepwise increase of the geomagnetic field (DL) is now clearly identified as a result of global compression o f the magnetosphere. The MI and PI are supposedly associated with transient magnetospheric field-aligned current (FAC) systems, but driven by different mechanisms. Magnetometers, riometers, optical images, satellite particle detectors, and ionospheric radars have become a standard tool for the monitoring the solar wind - magnetosphere - ionosphere coupling. For an examination of ionospheric response to solar wind pressure pulses Jayachandran et al. (2011) suggested to use the GPS global navigation satellite system. This technique providing information on total electron content (TEC) along a radiopath satellite - ground receiver has turned out to be sensitive enough to detect ionospheric response to transient and periodic disturbances in ULF band [Belakhovsky et al., 2016]. However, apossible mechanism o f the ionosphere modification by magnetospheric ULF disturbance has not been firmly established yet. Therefore, examination of the impact on the ionosphere by disturbances of different physical nature with simultaneous data from magnetometers, riometers, ionospheric radars, and GPS/TEC receivers may provide an insight into the mechanism o f magnetosphere-ionosphere coupling. In this paper we consider the ionospheric response to the IP shock as observed by ground magnetometers, riometers, aurora imagers, GPS receivers, and EISCAT radar. We discuss what features o f the SC-related phenomena are well understood, and what still require a further consideration and modeling. 100