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Observations of Asymmetric Lobe Convection for Weak and Strong Tail Activity.

Observations of Asymmetric Lobe Convection for Weak and Strong Tail Activity.

Authors :
Ohma, A.
Østgaard, N.
Reistad, J. P.
Tenfjord, P.
Laundal, K. M.
Moretto Jørgensen, T.
Haaland, S. E.
Krcelic, P.
Milan, S.
Source :
Journal of Geophysical Research. Space Physics; Dec2019, Vol. 124 Issue 12, p9999-10017, 19p
Publication Year :
2019

Abstract

In this study we use high‐quality convection data from the Electron Drift Instrument on board Cluster to investigate how near‐Earth tail activity affects the average convection pattern in the magnetotail lobes when the interplanetary magnetic field has a dominating east‐west (By) component. Two different proxies have been used to represent different levels of reconnection in the near‐Earth tail: The value of the AL index and the substorm phases identified by the Substorm Onsets and Phases from Indices of the Electrojet algorithm. We find that the convection changes from a dominantly YGSM direction, but opposite in the two hemispheres, to a flow oriented more toward the plasma sheet, as the north‐south component of the convection increases when reconnection enhances in the near Earth tail. This result is consistent with recent observations of the convection in the ionosphere, which suggest that the nightside convection pattern becomes more north‐south symmetric when tail reconnection increases. This is also supported by simultaneous auroral observations from the two hemispheres, which shows that conjugate auroral features become more symmetric during substorm expansion phase. The reduced asymmetry implies that the asymmetric pressure balance in the lobes is altered during periods with strong reconnection in the near‐Earth tail. Key Points: Average lobe convection when IMF By≠0 is more north‐south aligned for high |AL| compared to low |AL|Average lobe convection when IMF By≠0 is more north‐south aligned during substorms compared to nonsubstorm intervalsThe more north‐south aligned convection implies that enhanced near‐Earth tail reconnection alters the average lobe convection [ABSTRACT FROM AUTHOR]

Details

Language :
English
ISSN :
21699380
Volume :
124
Issue :
12
Database :
Complementary Index
Journal :
Journal of Geophysical Research. Space Physics
Publication Type :
Academic Journal
Accession number :
141383319
Full Text :
https://doi.org/10.1029/2019JA026773