报告人：英国南安普敦大学 Robert Fear教授

报告题目：Transpolar arcs - Earth's high latitude auroras

时间：5月3日 15:00-16:30

地址：闻天楼南楼208室

Presentation Title:

“Transpolar arcs - Earth's high latitude auroras”

by

Robert Fear

University of SouthamptonAbstract:

The Earth's auroras typically form in an oval configuration around the magnetic poles, encircling a dim region called the polar cap. The most vivid auroral displays, and many of the dynamical processes in the Earth's magnetosphere, occur when the interplanetary magnetic field (IMF) is southward. However, the behaviour of the magnetosphere and aurora when the IMF is northward is far more poorly understood. One particularly puzzling phenomenon is the transpolar arc - an auroral feature which extends into the polar cap from the night side of the main auroral oval. A multitude of possible mechanisms has been proposed to explain the formation of transpolar arcs, and these mechanisms differ in the predictions that they make. In this seminar we review the mechanisms which have been suggested, and discuss some statistical and case studies which demonstrate that transpolar arcs are formed by the occurrence of magnetic reconnection in the magnetotail, which closes magnetic flux in the nightside magnetosphere. Unlike the standard Dungey Cycle paradigm, this newly-closed flux is unable to convect back to the day side, and so it builds up in the magnetotail; the precipitation on these field lines gives rise to the transpolar arc.

Biography:

Dr Robert Fear is an STFC Ernest Rutherford Fellow and Principal Research Fellow at the University of Southampton (UK), where he is also Head of the Space Environment Physics group. He did his PhD at University College London’s Mullard Space Science Laboratory, and was a postdoc at the University of Leicester before moving to Southampton. His research interests cover spacecraft and ionospheric observations of large-scale solar wind/magnetosphere/ionosphere coupling (primarily at Earth), and he has specific interests in time-varying reconnection at the magnetopause (flux transfer events) and polar cap auroral phenomena (polar cap arcs, transpolar arcs).