Abstract
AbstractIt is known that the magnetic field of the Earth's closed magnetosphere can be highly displaced from the quiet‐day configuration when interacting with the interplanetary magnetic field (IMF), an asymmetry largely controlled by the dawn‐dusk component of the IMF. The corresponding ionospheric convection has revealed that footprints in one hemisphere tend to move faster to reduce the displacement, a process we refer to as the restoring of symmetry. Although the influence on the return flow convection from the process of restoring symmetry has been shown to be strongly controlled by the IMF, the influence from internal magnetospheric processes has been less investigated. We use 14 years of line‐of‐sight measurements of the ionospheric plasma convection from the Super Dual Auroral Radar Network to produce high‐latitude convection maps sorted by season, IMF, and geomagnetic activity. We find that the restoring symmetry flows dominate the average convection pattern in the nightside ionosphere during low levels of magnetotail activity. For increasing magnetotail activity, signatures of the restoring symmetry process become less and less pronounced in the global average convection maps. We suggest that tail reconnection acts to reduce the asymmetric state of the closed magnetosphere by removing the asymmetric pressure distribution in the tail set up by the IMF By interaction. During active periods the nightside magnetosphere will therefore reach a more symmetric configuration on a global scale. These results are relevant for better understanding the dynamics of flux tubes in the asymmetric geospace, which is the most common state of the system.
Highlights
The Earth’s magnetospheric response to solar wind forcing can to a large extent be explained as a two-stage process
As our focus is on the effect of various levels of tail activity on the convection of closed field lines, we only present the nightside part of the global convection maps
In our analysis we focus on the trends of this ratio rather than the value itself, which to some extent will reduce the impact of possible biases introduced when quantifying the convection speed, as, for example, correction for the corotation of the radars in the magnetic local time (MLT)/magnetic latitude (MLAT) frame
Summary
The Earth’s magnetospheric response to solar wind forcing can to a large extent be explained as a two-stage process. Despite knowing that the combination of the two stages controls most of the large-scale dynamics, it is often convenient to separate effects and look at influence on the system by one of the two in order to gain detailed insight One such example is the numerous studies of interplanetary magnetic field (IMF) clock angle influence on various high-latitude large-scale electrodynamic properties such as electric and magnetic fields, currents, convection, conductivity, etc. Such studies mostly agree on the large-scale features of the global distributions of these parameters in response to IMF clock angle Their main caveat is that they are large statistical averages, often sorted only by the IMF orientation and magnitude. They mix times when only Stage 1 dominates (i.e., largely controlled by the IMF clock angle), and times when significant nightside reconnection is present, which drastically changes the state of the system
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