Plasma Physics (Physics/ECE/NE 922) Seminars

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How does the magnetosphere go to sleep? Combining global scale simulations and observations to reveal fundamental behaviors of the magnetosphere
Date: Monday, February 3rd
Time: 12:05 pm - 12:55 pm
Place: 2241 Chamberlin Hall
Speaker: Therese Moretto Jørgensen, University of Bergen, Norway
Abstract: The Earth's magnetic field presents an obstacle to the streaming magnetized plasma of the solar wind, thereby creating the magnetosphere. The solar wind, magnetosphere, and ionosphere together constitute a fascinating, complex, and highly dynamic system of interacting plasmas in the space environment near Earth, which we can study with satellites and ground-based observations. Much has been learned over the last several decades about the dynamics of this system and the processes involved but many intriguing questions remain. This talk will present a recent study of one such interesting question in magnetospheric research related to the transition between magnetospheric configurations under substantial solar wind driving, and a putative relaxed state after the driving ceases.

Energy and circulation in the Earth’s magnetosphere and ionosphere are largely determined by conditions in the solar wind and interplanetary magnetic field. When the driving from the solar wind is turned off (to a minimum), we expect the activity to die down but exactly how this happens is not known. Utilizing global MHD modelling, we have addressed the questions of what constitutes the quietest state for the magnetosphere and how it is approached following a northward turning in the IMF that minimizes the driving. We observed an exponential decay with a decay time of about 1 hr in several integrated parameters related to different aspects of magnetospheric activity, including the total field-aligned current into and out of the ionosphere. The time rate of change for the cessation of activity was also measured in total field aligned current estimates from the AMPERE project, adding observational support to this finding.

The talk will give a brief introduction to magnetosphere research and the background for the study. The simulation models and observational data will be presented and the results will be explained and discussed in terms of their physical interpretation as it relates to magnetosphere dynamics and magnetosphere-ionosphere coupling.
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