South‐North Hemispheric Asymmetry of the FAE Distribution Around the Cusp Region: Cluster Observation. Issue 7 (16th July 2019)

• Record Type: Journal Article
• Authors: Shi, Jiankui; Zhang, Ziying; Torkar, Klaus; Cheng, Zhengwei; Escoubet, Phillipe; Farzakeley, Andrew; Dunlop, Malcolm; Carr, Chris
• Is Part Of: Journal of geophysical research. Volume 124:Issue 7(2019)
• Page Start: 5342
• Page End: 5352
• Publication Date: 2019-07-16
• Subjects: FAE events -- cusp region -- north‐south asymmetry -- Cluster observation; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2019JA026582
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: Cluster data from late July to early October were used to study the distribution of field‐aligned electron (FAE) events around the two cusps. An FAE event was defined as electron parallel flux >3 × 10 8 (cm 2 s) −1 . The total number of FAE events around the two cusps was basically identical, but downward FAE events prevailed in the south and upward FAE events in the north. In the southern cusp, the peak of the FAE events distribution versus altitude was about 1.3 R E higher and the peak of the FAE events distribution versus invariant latitude (ILAT) was about 4° ILAT lower. Only the downward FAEs around the southern cusp had a second ILAT peak, which was located about 11° higher than the main peak. The normalized number of FAEs showed nearly the same features as the unnormalized number of the FAEs events. These results indicated a north‐south asymmetry of the FAE distribution around the two cusps. Some causes for the asymmetry are discussed, the main ones being the asymmetry of the magnetospheric configuration resulting from geomagnetic dipolar tilt and solar wind flows, the interplanetary magnetic field asymmetry related to the magnetosphere, and the difference of ionospheric conductivity in the two hemispheres. Various solar wind‐magnetosphere interaction processes, such as quasi‐viscous interaction and reconnection, are responsible for the asymmetry, too. The second distribution peak (at higher ILAT) of the downward FAE events around the southern cusp corresponded to high solar wind speed and may be associated with the northward interplanetary magnetic field B z field‐aligned current at low altitude. This requires further studies, however. Key Points: It is the first time to investigate and find the north‐south hemispheric asymmetry of FAE distribution in the two cusps The asymmetry appeared in total FAE number, distribution versus altitude and ILAT, both for up and down directions It is important to understand the physics mechanism of the particles distribution and dynamics in the cusps and magnetosphere