Evolution of High-Latitude Geomagnetic Disturbances during the Magnetic Storm of July 22, 2009

Abstract

The behavior of geomagnetic disturbances during a moderate CIR storm, the most intense magnetic storm of 2009 in the solar activity minimum are considered. It is found that the substorm activity during the main phase of the storm was observed not in the nighttime but in the morning sector (0700–0900 MLT) of auroral geomagnetic latitudes (65°–67°) and was accompanied by extremely large (up to 1000 nT) geomagnetic pulsations of the Рс5 range, evidently of a non-resonant nature; the amplitude of the Y component of waves considerably exceeded that of the Х component. In the recovery phase of the magnetic storm, the tangential discontinuity in the IMF caused a substorm observed near the polar boundary of the auroral oval in the global scale in the longitude, from the evening sector to midday hours. In the daytime sector, the magnetic bay was observed several minutes later than in the nighttime sector and rapidly moved to the pole, which can be interpreted as the motion to the pole of the boundary between closed and open geomagnetic field lines and contraction of the auroral oval.