Radial Interplanetary Magnetic Field‐Induced North‐South Asymmetry in the Solar Wind‐Magnetosphere‐Ionosphere Coupling: A Case Study

Abstract

The paradigm that magnetospheric convection is driven by the process of magnetic reconnection between the interplanetary magnetic field (IMF) and terrestrial magnetic field was first proposed by Dungey (1961). Following this seminal work, enormous attention has been paid to the influence of the IMF orientation on the solar wind-magnetosphere interaction and its influence on the large-scale plasma convection in the high-latitude (polar and auroral) ionosphere (Milan & Grocott, 2021, and references therein). Previous studies pointed out that among three components of the IMF in geocentric solar magnetospheric (GSM) coordinates, the north-south (vertical) component (that is, IMF B z ) largely determines the global convection pattern of the plasma in the high-latitude ionosphere of both the Northern and Southern Hemispheres. Specifically, this consists of two vortex cells with an anti-sunward flow across the polar cap and a sunward return flow at lower latitudes in the morning and evening sectors (a two-cell convection pattern) under purely southward IMF conditions. When IMF is northward, on the other hand, two additional cells with reversed vorticity (a four-cell convection pattern) can exist in the central polar cap. These convection cells are observed to be significantly distorted toward either the dawn or dusk sector depending on the sign of dawn-dusk (azimuthal) IMF component (IMF B y ) (Heppner & Maynard, 1987). The convection pattern essentially shows a mirrored symmetry with respect to the noon-midnight meridian between the hemispheres.Compared to these two IMF components, less attention has been paid to the influence of the Sun-Earth (radial) IMF component (IMF B x ) on the solar wind-magnetosphere-ionosphere (SW-M-I) coupling. This is because its

Statistical Features of Polar Cap North and South Indices in Response to Interplanetary and Terrestrial Conditions: A Revisit

“…Park et al. (2022) pointed out that the hemispheric asymmetry in the SW‐M‐I coupling in the polar cap induced by strong IMF B x can be responsible for the discrepancy between the concurrent PCN and PCS . According to them, under strong IMF B x conditions, dayside magnetopause reconnection can take place in one hemisphere where the IMF drapes southward along the magnetopause, while single‐lobe reconnection can occur in the other hemisphere where the IMF drapes northward along the magnetopause (also documented in Pi et al.…”

“…For strong IMF B x cases (i.e., in 0°≤ ψ < 30°bins and 150°≤ ψ ≤ 180°bins), on the other hand, the occurrence of the opposite-sign PCN-PCS pairs tend to have the preferred IMF B x orientations depending on the sign type and the MLT location of the PC index stations (third and fourth row panels of Figure 4; also see Figure S1). Park et al (2022) pointed out that the hemispheric asymmetry in the SW-M-I coupling in the polar cap induced by strong IMF B x can be responsible for the discrepancy between the concurrent PCN and PCS. According to them, under strong IMF B x conditions, dayside magnetopause reconnection can take place in one hemisphere where the IMF drapes southward along the magnetopause, while single-lobe reconnection can occur in the other hemisphere where the IMF drapes northward along the magnetopause (also documented in Pi et al (2017)).…”

Auroral Electrojet Activity for Long‐Duration Radial Interplanetary Magnetic Field Events

“…However, there is some evidence from other observational and simulation studies that solar wind energy can enter the ionosphere through the magnetosphere via magnetic reconnection processes even under radial IMF conditions (H.‐M. Li et al., 2021; Nykyri et al., 2019; Park et al., 2021, 2022; Tang et al., 2013; H. Wang et al., 2014). These inconsistencies imply that the role of IMF B x in the SW‐M‐I coupling process is still poorly understood.…”

“…According to their event study, the magnetosphere under the influence of a strong IMF B x component (more specifically, under sunward IMF conditions) can be characterized by an absence of viscous-type interaction between the solar wind and the magnetosphere, no substorm activity, weak or no electron precipitation into the polar cap, and weak and patchy ionospheric convection. However, there is some evidence from other observational and simulation studies that solar wind energy can enter the ionosphere through the magnetosphere via magnetic reconnection processes even under radial IMF conditions (H.-M. Li et al, 2021;Nykyri et al, 2019;Park et al, 2021Park et al, , 2022Tang et al, 2013;H. Wang et al, 2014).…”