GEM: Response of Global Ionospheric Currents to Substorms: Implication for the Electric Field Penetration to the Inner Magnetosphere

点击翻译按钮获取中文摘要

This proposal builds on surprising evidence from an earlier study by this group that perturbations in the equatorial electrojet (a narrow ribbon of strong dayside ionospheric current flowing along the magnetic dip equator) may actually be caused by bursts of auroral activity called substorms on the nightside at polar latitudes. During substorms, strong currents are diverted from large radial distances in the extended tail of the magnetosphere along magnetic field lines into and through the ionosphere on the nightside. The ionospheric segment of the current is seen as a strong auroral electrojet (AEJ) at polar latitudes. The equatorial electrojet (EEJ), on the other hand, is generated as a result of the interaction between neutral winds flowing away from a region of strong solar heating while dragging ions across magnetic field lines, and the unique geometry of strictly horizontal magnetic field lines at the dip equator. The association between these electrojets implies that electric fields are penetrating from the polar region as far as the dip equator during substorms. Even though weak by the time they reach the equatorial region, their signatures can be observed in the modulation of the intense equatorial electrojet. This is a proposal to investigate more completely the response of the equatorial electrojet to substorms and determine its global closure. The penetration of the auroral electric field to low-latitudes, and the shielding that inhibits or prevents this penetration, are open and compelling questions for understanding and more accurately predicting space weather, which ultimately has benefits to society. Significant broader impacts include the participation of high-school teachers and students during the summer in research associated with this project.To accomplish the goals of this project, the proposers will address two questions: (1) how does the auroral electrojet respond to substorms, and (2) how is the substorm-related change of the dayside EEJ connected with the nightside AEJ.They will use data from a network of ground magnetometers, which includes 7 ground stations around the dip equator and a meridional chain of stations, along with auroral images from the Polar and IMAGE satellites. To answer question 1, they will use publicly-available lists of substorms, along with these observations, to determine statistically how often the EEJ responds to substorm onsets either by intensifying or weakening, the magnetic local time dependence of the response, and whether it is changed by the preceding level of geomagnetic activity. To answer question 2, they will examine the magnetic deflection (a measure of electric current intensity) as a function of solar zenith angle and magnetic latitude to test the idea that the EEJ and AEJ are connected by meridional currents that flow around the terminator. This is a new idea and a unique aspect of this proposal.