Active role of the ionosphere in the magnetosphere-ionosphere coupling

Abstract:

Magnetosphere-ionosphere (M-I) coupling is a key element in the Sun-Earth connection and is of fundamental importance for understanding the dynamics of the magnetospheric storms and substorms. In the recent years, it has been increasingly realized by the space science community that in the M-I coupling, the ionosphere is not a passive medium with the magnetosphere acting as a driver, instead, the ionosphere can play significant active role. The active ionospheric role is not only important in the M-I processes initiated in the ionosphere, but can also significantly impact the M-I processes initiated or driven by the magnetosphere, for example, substorms. In addition, there are many sharp plasma gradients and small-scale electromagnetic structures in the high-latitude ionosphere. These small-scale structures are essential for the study of the dynamics of the M-I system as well as for space weather specification and forecast. Without including the active role of the ionosphere, which has its own characteristic spatial and temporal scales, into the M-I coupling, many of these small-scale physical processes at high latitudes cannot be well understood.   Over the years, Utah State University group has been using the approaches of theoretical analysis, numerical modeling, data assimilation, as well as model-observation comparison to systematically study the active role of the ionosphere in a number of high-latitude M-I coupling processes. In this presentation, we will specifically use the results from our numerical modeling and model-observation comparison studies of the polar cap arcs and the terminator field-aligned currents discovered by the USU data assimilation model to demonstrate the active role of the ionosphere in the M-I coupling and discuss its underlying physics.