Date of Award
Program or Major
Doctor of Philosophy
In-situ measurements in the magnetotail are sparse and limited to single points. In the ionosphere, on the other hand, there is a broad range of observations, including magnetometers, aurora imagers, and radars . Since the ionosphere is the mirror of the plasmasheet, it can be used as a monitor of the magnetotail dynamics. Thus, it is of great importance to understand the coupling process between the ionosphere and the magnetosphere in order to interpret the ionosphere and ground observations properly. In this dissertation, the global magnetohydrodynamic simulation model, OpenGGCM model, is used to investigate two of such coupling processes. The first part focuses on travel time and characteristics of waves produced in the magnetotail. These waves represent the onset of the tail reconnection and substorms in the ionosphere. To investigate signal propagation paths and signal travel times, single impulse or sinusoidal pulsations are launched at different locations of the plasmasheet, and the paths taken by the waves and the time that different waves take to reach the ionosphere is determined. We find that such waves take shorter time than previously assumed, and they generally travel faster through the lobes than through the plasma sheet. It takes approximately about 70 seconds for waves to travel from the midtail plasmasheet to the ionosphere, contrary to previous reports (~ 200 seconds) [Ferdousi and Raeder, 2016]. Other important processes that greatly contribute to convection of the tail are bursty bulk flows (BBFs) which are identifiable as aurora streamers in the ionosphere. The second part of this thesis focuses on mapping such flows from the magnetotail to the ionosphere along the magnetic filed lines for three states of the magnetotail: before the substorm onset, during substorm expansion, and during steady magnetic convection event. We find that the streamers are north-south aligned in midnight area, and they have more east-west orientation in the dawn and dusk regions. The tail and the ionosphere activity increases during SMC event compared to the pre-onset and quiet times. We also find that, the convection background in the tail controls the direction and deflection of the BBFs and orientation of the aurora streamers in the ionosphere.
Ferdousi Shahandashti, Banafsheh, "The Study of Magnetotail Dynamics and their Ionospheric Signatures using Magnetohydrodynamic Simulation Model: OpenGGCM" (2017). Doctoral Dissertations. 147.