High-latitude geomagnetic pulsation response to the passage of the front edge of the interplanetary magnetic cloud of January 10, 1997

Abstract In this paper we studied the high-latitude long period geomagnetic pulsations excited during the first hours (0430– 0830 UT ) of the magnetic cloud impact on January 10, 1997. In this study we analysed the ground-based data of the IMAGE magnetometers and the Scandinavian network of ∼30 MHz riometers. Two time intervals were selected. The first interval (0430– 0600 UT ) corresponds to the passage of the compression region on the front edge of the magnetic cloud. During this interval bursts of geomagnetic and riometer data pulsations at frequency range of 1– 3 mHz as well as a magnetic substorm were observed at polar latitudes ( Λ >72°) with the strongest amplitudes near a footprint of the open/closed field lines boundary. The waves propagated rapidly eastward at ∼6– 7 km / s and had an azimuthal wave number m ∼12. This seems to be inconsistent with the main signature of a field line resonance. The green (557.7 nm ) optical emissions were observed at that time at Spitzbergen. The emissions moved rapidly eastward at about the same speed. We speculate that high-latitude geomagnetic pulsations under consideration were excited at the ionosphere altitudes, near the polar cusp footprint. The waves could be associated with quasi-periodic variations in the ionospheric conductivity produced by the particle precipitation oscillations. As the alternative hypothesis we could assume the direct penetration of solar wind compression or Alfven waves to the polar cap. These waves can modulate the particle precipitation produced the quasi-periodic variation of ionospheric conductivity. The second time interval (0600– 0830 UT ) corresponds to an abrupt increasing of the solar wind dynamic pressure, observed about 2 h after the passage of the leading edge of the magnetic cloud. Contrary to the first interval, the strongest amplitudes of geomagnetic and cosmic noise absorption pulsations were observed in closed magnetosphere, at Λ ∼66°, and showed the properties of the typical field line resonance.