South‐north asymmetry of field‐aligned currents in the magnetotail observed by Cluster

Abstract

[1] We statistically investigated features of the field-aligned current (FAC) distribution in plasma sheet boundary layers between 17 and 19 R E in the magnetotail using the curlometer technique to calculate the current from four-point magnetic field measurements taken in 2001. The results show that the FAC distribution in the plasma sheet boundary layers in the magnetotail has dusk-dawn asymmetry, earthward-tailward (polarity) asymmetry, and north-south asymmetry. The occurrence and polarities of FACs in the Northern Hemisphere are different from those in the Southern Hemisphere. The average density and the standard deviation of the FACs that are most likely to be connected to the Earth are 4.90 nA m −2 and 2.55 nA m −2 in the Northern Hemisphere and 4.21 nA m −2 and 1.80 nA m −2 in the Southern Hemisphere, respectively. For investigating the mechanism of the north-south asymmetry, we mapped the FACs along the field line into the polar region. The footprints of the FACs also show a difference between the Southern and Northern hemispheres (as a function of mapped latitude). These characteristics suggest a north-south asymmetry of the FACs in the magnetosphere. Further investigation is needed to identify the causes of this asymmetry, although the configuration of the magnetosphere, the polar cap boundary, the conductivity in the ionosphere, or the various solar wind-magnetosphere interaction processes all may be contributors. That the FAC densities are different between the hemispheres suggests that an important source of these currents must be a voltage generator.

Influences of the interplanetary magnetic field clock angle and cone angle on the field‐aligned currents in the magnetotail

“…The other is using the plasma ß (the ratio of plasma pressure to magnetic pressure). In this study, we generally identify the PSBL by examining the geomagnetic field components B x , B y , and B xy () [ Ohtani et al ., ; Shi et al ., ]. When the geomagnetic activity is strong and the geomagnetic disturbance is violent, however, it is too difficult to identify the PSBL accurately using this method.…”

Electromagnetic Fields of Magnetospheric ULF Disturbances in the Ionosphere: Current/Voltage Dichotomy

“…On the other hand, in the case of voltage generator, the amount of total current strongly varies with seasonal dependence on the ionospheric conductance. Studies using this analysis found global magnetospheric FAC systems (Haraguchi et al, 2004;Shi et al, 2010) and SCs (Shinbori et al, 2012) should be attributed to voltage generators.…”

Statistics of the field‐aligned currents at the high‐latitude energetic electron boundaries in the nightside: Cluster observation

“…So it is necessary to do systematic statistics to explore which current system generates the magnetic field bipolar signatures at the high-latitude energetic electron boundary. The Cluster constellation is in a high-eccentricity polar orbit which also provides a good opportunity to study the FACs and their source regions at perigee and has its own advantages in comparison with low-latitude satellites [e.g., Iijima and Potemra, 1976a;Le et al, 2010] and spacecraft observations during the crossing of the plasma sheet [e.g., Elphic et al, 1985;Ueno et al, 2002;Shi et al, 2010]. The regions 1 and 2 currents, detected by the low-latitude satellites, are close to each other [Iijima and Potemra, 1976a;Le et al, 2010], which will separate in the distant region [Tsyganenko and Stern, 1996].…”