U.S.-Western Europe Cooperative Study of the Solar Wind Acceleration

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This award supports Dr. W. A. Coles and two graduate students of the University of California at San Diego to collaborate in space physics research with Ruth Esser and others of the Auroral Observatory, University of Tromso, Norway, Egil Leer of Oslo, Jussi Markkanen of Finland, and Eckart Marsch of the Max Planck Institute for Aeronomy, Lindau, Germany. Much of the leading theoretical work on solar wind acceleration is now done in Europe (notably in Norway and at this German institute.) The U.S. PI and his students will benefit substantially from the opportunity to work directly with these leading theorists. Together they propose to continue observations of the solar wind velocity that were begun at the European Incoherent Scatter Radar Facility (EISCAT) in northern Scandinavia during the summer of 1990, when Dr. Coles was on sabbatical. Despite limits on the observing time, the 1990 data have permitted the first quantitative comparison of theoretical radial acceleration profiles with measurements. More time will be available to them in the coming few summers, which will enable them to make many more observations and drastically decrease the velocity estimation errors. This extra observing time does require much more work, and the graduate students as well as several European collaborators are necessary for its success. The basic aim of this proposal is to improve understanding of the earth's plasma environment. The plasma is formed by ionization of the atmosphere by solar radiation. This "ionosphere" interacts with the outer atmosphere of the sun, the "solar wind", in a magnetically controlled region called the "magnetosphere." The proposed collaborative research is directed at understanding the mechanisms which create and accelerate the solar wind, causing the sudden changes in its velocity which are responsible for ionospheric disturbances. Such disturbances have a number of important geophysical and practical symptoms, including auroral displays, high frequency communications blackouts, fading on satellite communication links, and long distance power line upsets.