Influence of the IMF cone angle on invariant latitudes of polar region footprints of FACs in the magnetotail: cluster observation
File(s)
Author(s)
Type
Journal Article
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/m 2 ) 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.
Date Issued
2018-04-06
Date Acceptance
2018-03-08
Citation
Journal of Geophysical Research: Space Physics, 2018, 123 (4), pp.2588-2597
ISSN
2169-9380
Publisher
American Geophysical Union
Start Page
2588
End Page
2597
Journal / Book Title
Journal of Geophysical Research: Space Physics
Volume
123
Issue
4
Copyright Statement
©2018 American Geophysical Union.
Sponsor
Science and Technology Facilities Council (STFC)
Science and Technology Facilities Council (STFC)
Science and Technology Facilities Council (STFC)
Science and Technology Facilities Council (STFC)
Grant Number
ST/L001276/1
ST/M003116/1
ST/N002784/1
ST/P003427/1
Subjects
Science & Technology
Physical Sciences
Astronomy & Astrophysics
FAC in magnetotail
footprints in polar region
IMF cone angle
FIELD-ALIGNED CURRENTS
INTERPLANETARY MAGNETIC-FIELD
CURRENT SIGNATURES
NORTHWARD IMF
AURORAL OVAL
DEPENDENCE
BOUNDARY
CHAMP
RECONNECTION
LOCATION
Publication Status
Published
Date Publish Online
2018-03-13