Influence of the IMF Cone Angle on Invariant Latitudes of Polar Region Footprints of FACs in the Magnetotail: Cluster Observation

Abstract

The influence of the interplanetary magnetic field (IMF) cone angle θ (the angle between the IMF direction and the Sun‐Earth line) on the invariant latitudes of the footprints of the field‐aligned currents (FACs) in the magnetotail has been investigated. We performed a statistical study of 542 FAC cases observed by the four Cluster spacecraft in the Northern Hemisphere. The results show that there are almost no FACs when the IMF cone angle is less than 10°, and there are indications of the FACs in the plasma sheet boundary layers being weak under the radial IMF conditions. The footprints of the large FAC (>10 nA/m2) cases are within invariant latitudes <71° and mainly within IMF cone angles θ > 60°, which implies that the footprints of the large FACs mainly expand equatorward with large IMF cone angle. The equatorward boundary of the FAC footprints in the polar region decreases with increasing IMF cone angle (and has a better correlation for northward IMF), which shows that the IMF cone angle plays an important controlling role in FAC distributions in the magnetosphere‐ionosphere coupling system. There is almost no correlation between the poleward boundary and the IMF cone angle for both northward and southward IMF. This is because the poleward boundary movement is limited by an enhanced lobe magnetic flux. This is the first time a correlation between FAC footprints in the polar region and IMF cone angles has been determined.

Environmental Conditions During the Reported Charging Anomalies of the Two Geosynchronous Satellites: Telstar 401 and Galaxy 15

“…There are several previous studies on the influence of one of the components of the IMF in the entrance of energy from the solar wind to the magnetosphere‐ionosphere system and on the asymmetries associated with the relevant role played by any IMF component by minimizing the role of the others (Belenkaya et al, ; Chakrabarty et al, ; Cheng et al, , ; Liou et al, ; Ostgaard et al, , ; Tenfjord et al, ; Wing et al, ). However, the IMF influence on the FACs in the magnetotail should be a combined contribution of all IMF components and not only from a single one (Cheng et al, ).…”

Interplanetary Magnetic Field By Effects on the Strength and Latitude of Field‐Aligned Currents in Different Magnetic Local Time Sectors

“…The FACs intensity is effectively controlled by the solar wind merging electric field, E m , which characterizes the combined influence of IMF B y and B z magnitudes, and is symmetrical with respect to the polarity of the IMF B y component (e.g., Cheng et al., 2018; Huang et al., 2017; Kervalishvili and Lühr, 2014; Wang et al., 2005). However, the hemispheric differences in the auroral intensities and electromagnetic energy input have been revealed to depend on the orientation of IMF B y and solar illumination (e.g., Hu et al., 2014; Liou & Mitchell, 2020; Liu et al., 2020; Østgaard et al., 2011; Pakhotin et al., 2021).…”

Impact of the Solar Wind Dynamic Pressure on the Field‐Aligned Currents in the Magnetotail: Cluster Observation

“…There was a clear north–south hemispheric asymmetry of the polarity of the FACs for both signs of IMF B y , and this asymmetry of the polarity was more distinct when IMF B y was positive. Further research showed that the occurrence, density, and the location of the footprint of the FAC were depending on the IMF clock and cone angle (Cheng et al., 2013, 2018).…”