ABSTRACT

This is a three-year project to investigate a remarkable new finding, that the intensity of geomagnetic storms displays distinct universal time dependence, and that it varies in concert with middle latitude ionospheric plasma abundance during storms. Geomagnetic indices provide our most consistent measure of physical processes occurring in geospace since their creation over the last century. The strength of geomagnetic storms, most notably, is captured in the so-called Dst index, calculated from a set of four ground-based magnetometer measurements located strategically around the Globe. This project will utilize a newly derived, improved Dst index dataset to carry out a detailed examination of trends in the storm-time Dst with UT, season and solar cycle. Ionospheric plasma adds greatly to the pressure, pressure gradients, and currents in the magnetosphere, the last of which are measured on the ground to indicate magnetic storm strength. Ion outflow in the auroral zone, particularly in the dayside ?cusp? and nightside tail-reconnection region, provides most of this plasma. The abundance of ionospheric plasma at high latitudes has recently been shown to be a more complex process than previously thought, with a number of processes delivering plasma from middle to high latitudes in rapid fashion during periods of enhanced magnetic activity. A UT-dependent modulation of outflow during enhanced magnetic activity is one possible explanation for the observed variation in magnetic storm strength. The examination of how ionospheric ion outflow into the magnetosphere may vary during different storms and impact the UT dependence of the Dst index is the main overarching objective for this project. A parallel effort will examine whether the UT dependence in the observations is also reproduced by first-principles models of the coupled physical system. The project will use the suite of ionosphere-thermosphere-magnetosphere models that make up the University of Michigan Space Weather Modeling Framework.

The project has impacts beyond the immediate benefits of improved scientific understanding. Students will participate in all aspects of the work, both at U. Michigan and Berkeley, results will be submitted to widely-read publications, and the team will work with the Center for Science Education at Berkeley to make the findings accessible to the network of teachers that it works with around the country on magnetometer data and magnetism. The importance of determining whether magnetic storms are indeed more powerful in the afternoon in the United States during summer can hardly be overstated, particularly in light of recent National Academy findings of the likely economic costs to the U.S.A. of a truly major geomagnetic storm.