Overview of Solar Wind–Magnetosphere–Ionosphere–Atmosphere Coupling and the Generation of Magnetospheric Currents

Abstract

We review the morphology and dynamics of the electrical current systems of the terrestrial magnetosphere and ionosphere. Observations from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) over the three years 2010 to 2012 are employed to illustrate the variability of the field-aligned currents that couple the magnetosphere and ionosphere, on timescales from minutes to years, in response to the impact of solar wind disturbances on the magnetosphere and changes in the level of solar illumination of the polar ionospheres. The variability is discussed within the context of the occurrence of magnetic reconnection between the solar wind and terrestrial magnetic fields at the magnetopause, the transport of magnetic flux within the magnetosphere, and the onset of magnetic reconnection in the magnetotail. The conditions under which the currents are expected to be weak, and hence minimally contaminate measurements of the internallyproduced magnetic field of the Earth, are briefly outlined.

Field‐Aligned and Horizontal Currents in the Northern and Southern Hemispheres From the Swarm Satellite

“…Nevertheless, the average horizontal and FACs in the two hemispheres have often been assumed symmetrical, when averaged over seasons and solar wind conditions. Coxon et al (2016) and Milan et al (2017) used also Iridium data, now as part of the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) experiment. Green et al (2009) used the Iridium constellation to study the dependence of the global FAC configuration on IMF direction and magnitude, hemisphere, and season.…”

On the role of neutral flow in field-aligned currents

“…We discuss a perspective on ionospheric electrodynamics that emphasizes the importance of ion-neutral velocity differences within the high-latitude ionosphere (see also Tu et al, 2011, andVasyliunas, 2012). To the extent that such velocity differences are not caused by currents originating with magnetospheric processes, this perspective de-emphasizes magnetospheric current systems as a primary causative factor in magnetosphere-ionosphere coupling (however, see Milan et al, 2017;Milan, 2013;Thayer and Semeter, 2004;Cowley, 2000;Kan, 1987). We are inferring cause and effect relationships based on momentum balance considerations, not considerations of what changes the inertia of the charged or neutral species.…”

“…This solution is not of interest during conditions leading to geomagnetic storms. The solar wind imparts momentum to ionospheric ions via electrodynamic forces, as is well known from observations of ion convection anti-sunward over the polar cap (Milan, 2017). The neutral species will be influenced by ion-neutral collisions and other forces, such as gravity and pressure forces due to coupling from below, and in general neutrals will be at a different velocity than the ions.…”

Interhemispheric Asymmetry in Response of Low‐Latitude Ionosphere to Perturbation Electric Fields in the Main Phase of Geomagnetic Storms

“…Magnetohydrodynamical representation of flow of plasma needs pressure gradient forces excited by the magnetospheric dynamo that map the R1 and R2 FACs to the polar latitude ionosphere acting as load (Milan et al, 2017;Tanaka et al, 2016). The R1 (R2) FAC flows into the poleward (equatorward) boundary of auroral latitudes in midnight-noon (noon-midnight) sector centered around dawn (dusk) and flowing out of auroral ionosphere in noon-midnight (midnight-noon) sector centered around dusk (dawn).…”

“…The equatorward winds launched during the MP of the storm later on reach the middle and middle-to-low latitudes forming the disturbance dynamo wind system that produces opposing electric fields to the prevailing fields (Blanc & Richmond, 1980;Fuller-Rowell et al, 2002;Fejer et al, 2016), whereas the convection electric field associated with interplanetary electric field (IEF Ey), derived as IEF Ey = −Vsw × Bz, is transmitted instantaneously from high latitudes to the dip equator (Senior & Blanc, 1984), known as prompt penetration electric field (PPEF; Kikuchi & Araki, 1979;Kelley et al, 1979;Kikuchi et al, 1996Kikuchi et al, , 2008. As far as PPEF is concerned, its magnitude and efficiency during each case vary for daytime and nighttime conditions with anomalous dawn and dusk behaviors (Hashimoto et al, 2017;Kikuchi et al, 2008;Milan et al, 2017;Peymirat et al, 2000). PPEF can immediately affect the equatorial ionospheric TEC (total electron content) when compared to TADs during the MP (Dashora et al, 2009;Maruyama et al, 2005).…”