Studies of Magnetospheric Convection: Balanced and Unbalanced.

Abstract

During active times, the magnetosphere can enter into different modes of convection. Three of the most common modes are: steady magnetospheric convection (SMC), isolated substorms, and sawtooth injections. This thesis investigates the differences in solar wind conditions and magnetospheric dynamics during these three modes. Using Polar UVI and IMAGE FUV auroral images, the open-closed magnetic field line boundary is measured using an intensity cut off. The magnetic field inside this boundary is integrated over the interior area to calculate the amount of open magnetic flux in the polar cap (Fpc). The Fpc is an indicator of the balance of dayside and nightside reconnection rates, thus its temporal evolution varies for different convection modes. If magnetospheric convection is steady, SMC mode, then the Fpc will be stable over time. If the Fpc increase (decreases) then most like the dayside (nightside) reconnection rate is larger than the nightside (dayside). The first of three studies analyzes four different SMCs and examines how balanced reconnection intervals begin and end. The second study includes a case study of each different convection mode. It also includes a superposed epoch analysis of the Fpc for all three modes. Finally, a statistical analysis is performed on the solar wind and IMF drivers that occur during the different convection modes. These three studies show for the first time that: (1) Not all SMCs are alike in their termination of balanced reconnection or in their activity levels; (2) On average, SMCs and substorms have similar amounst of Fpc, while both substorms and sawteeth release approximately 30% of their Fpc during the unloading process; (3) Finally,while the IMF Bz is steady for both sawteeth and SMCs, the solar wind velocities are very different, suggesting that more than just IMF Bz determines what mode of convection the magnetosphere enters.