Solar Cycle, Solar Wind, and Ultraviolet (UV) Control of Substorm Frequency and Magnitude

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Magnetospheric substorms are one of the most widely studied and important topics in magnetospheric physics. Substorms are frequent and studies of substorms allow researchers to investigate the basic physics of the dynamics of the solar wind, magnetosphere and ionosphere system. It is well recognized that magnetic reconnection occurs at the dayside magnetopause in the overwhelming majority of substorms and is generally thought to be the main way in which mass, momentum and energy are transported from the solar wind to the magnetosphere. However, other processes can also influence substorm dynamics. This is a proposal to evaluate the importance of the solar wind velocity and ionospheric conductivity on substorm dynamics. It is possible to separate these effects from the effects of reconnection because of the large 30 year data base created by the SuperMAG project. In a substorm the magnetosphere is first preconditioned by the solar wind. This preconditioning has two time scales. In this proposal it is hypothesized that those time scales are influenced by the solar wind velocity. One influence affects the reconnection rate at the dayside magnetopause and the other provides ?seed energy? to the plasma sheet. The investigators also propose to investigate the influence of ionospheric conductivity on substorm preconditioning by studying the effects of solar UV insolation. In particular they will investigate the semi-annual variation of geomagnetic activity with peak activity at the equinoxes and the observation that during substorms stronger auroras occur in the winter hemisphere. They propose to resolve the question of whether dipole tilt (and hence reconnection) drives the equinoctial variation or whether UV insolation is also important. This work will support a young woman scientist just starting her career. The Applied Physics Laboratory has an ongoing program to support summer interns. The database from this study will be very valuable to the overall magnetospheric physics effort.