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 of Auroral Phenomena", Proc. XL Annual Seminar, Apatity, pp. 19-22, 2017 © Polar Geophysical Institute, 2017 Ьп/ЦЛл Geophysical у Institute EFFECT OF THE IMF By ON DAYSIDE POLAR GEOMAGNETIC DISTURBANCES: CASE STUDY L.I. Gromova, S.V. Gromov Pushkov Institute o f Terrestrial Magnetism, Ionosphere and Radio Wave Propagation, Moscow, Russia Abstract. We present a study of magnetic bay-like disturbances occurred in the dayside sector o f the polar geomagnetic latitudes on Jun 23, 2015 and on May 24, 2000 under similar IMF and the solar wind conditions. These dayside bays developed during untypical long-duration interval of the strong negative IMF Bz under invariable the solar wind velocity and low the solar wind dynamic pressure. On June 23, 2015 the long-duration dayside negative magnetic bay (~ -350 nT) was recorded at the high-latitude IMAGE stations while the IMF Bz was more intensive than the IMF By (the ratio of the \Bz\/\By | к 3). On May 24,2000 the sequence of positive and negative bays occurred in the dayside sector of the polar latitudes (Ф > 70°) under the positive or negative IMF By respectly, and the ratio of the \Bz\t\By | varied from 0.3 to 0.9. It is shown that examined dayside polar geomagnetic disturbances should be prodeced by different high latitude current systems controlled by IMF By. We suppose the IMF By effect on dayside polar geomagnetic disturbances substantially depends on the IMF \Bz\/\By\ ratio. Introduction It is well known, under a positive Bz component of the Interplanetary Magnetic field (IMF) there is no new energy input into the magnetosphere. But dayside polar bay-like magnetic disturbances could be occur associating with the high-latitude ionospheric electric currents [e.g., Iwasah, 1971; Friis-Christensen and Wilhjem, 1975; Feldstein et al., 2006]. The role of the ratio of IMF Bz and By components controlling the development of the high latitude geomagnetic disturbances has been described previously but mainly under a dominant IMF By component [e.g. Friis- Christensen et al, 1985; Vennerstrom et al., 2002]. The aim of our study is to show the role of the ratio of IMF Bz and By components in the dayside magnetic bay­ like disturbances occurrence. Here we studied two events of magnetic bay-like disturbances occurred in the dayside sector of the polar geomagnetic latitudes on Jun 23, 2015 and on May 24, 2000 under similar IMF and the solar wind conditions. Data Our study is based on the OMNI data [http://omniweb.gsfc.nasa.gov] , on the ground-based Scandinavian magnetometer data (IMAGE profile) [http://space.fmi.fi/MIRACLE] , observations by the DMSP [http://sd- www.jhuapl.edu/Aurora/spectrogram] and IMAGE [https://cdaweb.sci.gsfc.nasa.gov/cgi-bin/evall] low orbiting satellites, the OVATION model of the auroral oval location [http://sd-www.jhuapl.edu/Aurora/ovation] , and the AMPERE data, based on the magnetic measurements on 66 low-altitude globally distributed Iridium communication satellites [http://ampere.jhuapl.edu/products/plots] . k m /e 700 riFuf* 30 June 23, 2015 fl ]i ^ yl B y _ —'4» L.... !..............!....... I V - . ;аГ Figure 1. The IMF Bz and By, solar wind velocity V and dynamic pressure Psw, and the AL- index. 19