High-Latitude Geomagnetic Disturbances and Field Aligned Currents in the Recovery Phase of the Large Magnetic Storm on June 21–26, 2015

The features of the geomagnetic effect of the approach of an interplanetary magnetic cloud to the Earth’s magnetosphere during the recovery phase of a strong magnetic storm (June 21–26, 2015) are studied. On the Earth’s surface, the greatest geomagnetic effects were recorded when the leading edge of the magnetic cloud approached the Earth’s magnetosphere, where large alternating variations in the Bz and By components of the IMF were observed. Large (up to 1000 nT), bay-like magnetic disturbances were observed in the near-noon sector of the circumpolar latitudes, presumably in the region of the projection of the daytime polar cusp. It is shown that the sign of the high-latitude magnetic bay was controlled by the sign of the By component of the IMF and did not depend on the direction of the Bz component of the IMF. The planetary, high-latitude geomagnetic activity and the distribution of large-scale, field aligned electric currents calculated from magnetic observations were studied based on simultaneous magnetic registration on 66 ionospheric communication satellites (project AMPERE). It was found that, in the case of the development of a negative magnetic bay (the western electrojet), the downward field aligned electric currents in the midday sector were observed to be more polar than the upward currents. For a positive bay (the eastern electrojet), the upward currents were more polar than the downward ones. It is shown that an abrupt change in the sign of the By components of the IMF led not only to a sharp change in the direction of the ionospheric current, but also to its movement in latitude.