Space Physics and Aeronomy, Ionosphere Dynamics and Applications. Группа авторов

Space Physics and Aeronomy, Ionosphere Dynamics and Applications - Группа авторов


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magnetic disturbances observed at 1,100 kilometers in the auroral oval. Journal of Geophysical Research, Space Physics, 75(25), 4757–4762.

       Stephen E. Milan1,2, and Adrian Grocott3

       1 Department of Physics and Astronomy, University of Leicester, Leicester, UK

       2 Birkeland Centre for Space Science, University of Bergen, Bergen, Norway

       3 Physics Department, Lancaster University, Lancaster, UK

      ABSTRACT

      We review the excitation of high‐latitude ionospheric convection by the interaction of the solar wind with the magnetosphere and the coupling between the magnetosphere and ionosphere. We discuss the role of magnetic reconnection in driving the Dungey cycle of convection, and the influence of frictional coupling between the ionosphere and atmosphere in modifying this convection. The electric current systems that transport stress and momentum throughout the system are described, as well as the magnetic perturbations that they produce on the ground. The system is first described as a steady‐state approximation, and then the time‐dependent expanding/contracting polar cap model of the Dungey cycle is introduced, together with its relation to the substorm cycle.

      At high latitudes, the ionized part of the upper atmosphere undergoes a circulation known as convection, driven by the interaction between the magnetized solar wind and the Earth's magnetosphere. It is the purpose of this review to discuss the nature of this ionospheric convection and its causes. More detail on many aspects of the theory discussed here can be found in other recent reviews, including magnetosphere‐ionosphere coupling (Cowley, 2000), magnetic reconnection and convection (Chisham et al., 2008), magnetospheric current systems (Baumjohann et al., 2010; Ganushkina et al., 2015; Milan et al., 2017), and the history of the development of the ideas behind our current understanding of the system (Cowley, 2015; Milan, 2015), including dawn‐dusk asymmetries (Grocott, 2017). At the end of this review, we will place this chapter in the context of the other chapters in this monograph.

Schematic illustrations of average convection patterns for different IMF orientations from northward at the top and duskward at the right, for solar wind electric field between 3.0 and 20.0 mV m-1. Each panel is presented in a magnetic latitude (50o–90o) and magnetic local time coordinate system, with noon toward the top and dawn to the right. Contours of electrostatic potential are shown in steps of 5 kV.

      (from Thomas & Shepherd, 2018; Reproduced with permission of John Wiley and Sons).

      During the 1980s, it became clear that convection could be highly dynamic in response to intermittent phenomena such as changes in the IMF and magnetospheric processes such as substorms (e.g., Kamide & Vickery, 1983; Etemadi et al., 1988; Williams et al., 1989; Moses, 1989). A new, more dynamic picture of the Dungey cycle and its driving of ionospheric convection began to emerge, which recognized that the magnetosphere was driven independently by processes at the magnetopause and in the magnetotail (e.g., Russell, 1972; Holzer et al., 1986; Siscoe & Huang, 1985; Freeman & Southwood, 1988; Lockwood et al., 1990; Cowley & Lockwood, 1992; Lockwood & Cowley, 1992). To test these ideas, it was necessary to find techniques to instantaneously observe flows over large regions of the polar ionosphere, and systems such as the Super Dual Auroral Radar Network (SuperDARN) (Greenwald et al., 1995; Chisham et al., 2007) and Assimilative Mapping of Ionospheric Electrodynamics (AMIE) (Richmond & Kamide, 1988) were developed. Together with spacecraft missions to observe the large‐scale morphology of auroras, such as Polar (Acuña et al., 1997) and the Imager for Magnetopause‐to‐Aurora Global Exploration (IMAGE) (Burch, 2000), and FACs, such as the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) (Coxon et al., 2018, and references therein), a new picture of the time‐variability of convection has come about. This is discussed in section 2.4.

      This section provides a tutorial introduction to the morphology of the magnetosphere‐ionosphere system and the plasma physics that determines its dynamics. This will provide the background for sections 2.3


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