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.

“Physics o f Auroral Phenomena", Proc. XL Annual Seminar, Apatity, pp. 23-26, 2017 © Polar Geophysical Institute, 2017 Polar Geophysical Institute DAYSIDE POLAR SUBSTORM BEHAVIOR: CASE STUDY N.G. Kleimenova1,2, L.I. Gromova3, S.V. Gromov3, L.A. Dremukhina3, L.M. M alysheva1, N.E. V asilieva1 1 Schmidt Institute o f Physics o f the Earth (IFZ RAN), Moscow 2Space Research Institute, Moscow, Russia ^Pushkov Institute o f Terrestrial Magnetism, Ionosphere, and Radio wave Propagation, (IZMIRAN), Troitsk, Moscow Abstract. In our previous studies we have identified the specific polar-latitude (>70°) negative bay-like magnetic disturbances which are observed near the local noon under the northward IMF Bz. These disturbances occur on the contracted auroral oval similarly to the evening polar substorm. According to that, we call them “ dayside polar substorms ” and consider the polar-latitude NBZ field-aligned currents (FACs) as their plausible source. To confirm this hypothesis, we continued comprehensive detailed studies the dayside negative polar magnetic bays and present here the results of such analysis o f the data collected from the IMAGE magnetometer chain including the Svalbard during the initial phase of the magnetic storm on January 22, 2012. The discussed daytime substorm (09-11 UT) was observed under the northward IMF Bz and very strong negative IMF By (about -30 nT) with the ratio o f \By\/\Bz\ ~3. In the considered time interval, there were no magnetic disturbances in the night side of the Earth as well as at the auroral latitudes (Л/.-index <150 nT). The SUPERDARN radar data showed the significant change in the high-latitude ionosphere convection. Before and after the discussed dayside substorm, there was two-vortex convection distribution. When the IMF Bz became large positive, and the IMF By became large negative, the convection vortices weakened. However, some small additional vortices appeared near noon which could be interpreted as the NBZ type of FAC occurrence. The AMPERE data, based on the magnetic measurements on 66 globally distributed low-altitude satellites, demonstrated the counter-clockwise magnetic vortex above Svalbard stations and very intensive upward FACs which were surrounded by two layers of the downward currents, located to the north and south. These FACs could provide the necessary energy for the dayside polar magnetic bay generation. But, the source of these FACs is still unknown. Introduction In our previous papers [. Kleimenova et al., 2015; Levitin et al., 2015; Gromova et al., 2016] we have identified the specific polar-latitude (>70°) negative bay-like magnetic disturbances which are observed near the local magnetic noon under the northward IMF Bz. Similar disturbances have been previously reported by [Iwasaki, 1971; Friis- Christensen and Wilhjem, 1975; Feldstein, 1976]. The bay sign was mainly controlled by IMF By and was termed by [Friis-Christensen and Wilhjem, 1975] as DPY currents. These magnetic disturbances occur on the contracted auroral oval as well as the evening “polar substorms” discussed in [Kleimenva et al., 2012]. Due to that we call these daytime polar disturbances “dayside polar substorms”. An example of such very strong substorm with the amplitude in order of 1000 nT is shown in Fig. 1. The aim of this study is comprehensive analysis of the dayside negative polar magnetic bay observed during the initial phase o f the moderate magnetic storm on January 22, 2012. Data and observations Ground-based data. Our analysis was based on the 10 s sampled Scandinavian magnetometer chain (IMAGE) data. The moderate “dayside polar substorm” was observed on January 22, 2012 at 09-11 UT (12-14 MLT) under the northward IMF Bz (+10 nT) and very strong negative IMF By (-30 nT) with the ratio of \By\/\Bz\~ 3 (Fig. 2). The solar wind speed was ~500 km/s, however, the solar wind dynamic pressure before this substorm, i.e. during the initial phase of the magnetic storm, was very strong (>20 nPa) as it was discussed in [Rout et al., 2016]. There were no significant geomagnetic disturbances in the night side of the auroral zone (AL- index < -150 nT, Fig. 2). The AMPERE data. The AMPERE (Active Magnetosphere and Planetary Electrodynamics Response Experiment, the website http://ampere.jhuapl.edu) facility consists of 66 Iridium commercial satellites at 780 lan altitude with the polar circular orbits distributed over six orbital planes to provide global satellite data. Each satellite carries an engineering magnetometer. The spherical harmonic fitting technique is applied [Anderson et al., 2000] to estimate the global distribution of radial currents which in the polar regions correspond to the Birkeland currents or field-aligned currents (FACs) commonly associated with the region 1 (R l) and region 2 (R2) current system [Iijima and Potemra, 1976]. 23