The pulsating magnetosphere and flux transfer events

Abstract

A unique positioning of the GOES 5, GOES 6, AMPTE/CCE, and Viking satellites on the dayside of the magnetosphere has provided the opportunity to study the relationship of periodic variations in magnetic fields, energetic particle fluxes, and images of UV auroral forms. On March 25, 1986, at about 1725 UT, two cycles of 10‐min‐period magnetic field oscillations were observed by all four satellites and by the Huancayo magnetic ground station. The UV images acquired by Viking showed intense emissions in a wide area near noon at 1730 UT, but near dawn 11 min later. We interpret these observations as being associated with anti‐sunward‐moving periodic compressions of the magnetopause, which precipitated low‐energy electrons that produced the enhanced UV emissions. In the midst of the longer‐period variations, the magnetic field intensity measured by CCE near the magnetopause decreased sharply for a 105‐sec period. This may be interpreted as being due to a flux transfer event that occurred during the longer (10‐min) periodic compressions of the magnetosphere. These observations support the view that the magnetosphere often varies in a periodic way because of its own resonant processes and processes driven by the solar wind. A wide range of phenomena is associated with these variations including dayside auroral emissions, magnetic field variations throughout the magnetosphere and on the Earth's surface, and flux transfer events.