Measurements of the interplanetary solar wind during the large geomagnetic storm of April 17-18, 1965

Abstract

During the large geomagnetic storm of April 17–18, 1965, measurements of the solar wind were made with electrostatic analyzers on the Vela 2 satellites. A number of the observed solar wind changes can be related to worldwide geomagnetic changes; the most impressive event occurred after the main phase development when a fivefold increase in the solar wind density resulted in a sudden geomagnetic impulse. During the initial phase of the storm the plasma measurements were not complete, but the evidence indicates that the wind pressure increased at the time of the sudden commencement, and other features of the initial phase seem to have been related to solar wind changes. However, the main phase of the storm developed during a period when the solar wind remained relatively steady; further, there was nothing abnormal about the magnitude of the velocity, temperature, or proton density at that time. The α-particle flux during this period was higher than usual. The storm recovery was characterized by a period of rising solar wind velocity and temperature.