Response timescales of the magnetotail current sheet during a geomagnetic storm: Global MHD simulations

Eggington, J. W. B., Coxon, John, Shore, R. M., Desai, R. T., Mejnertsen, L., Chittenden, J. P. and Eastwood, J. P. (2022) Response timescales of the magnetotail current sheet during a geomagnetic storm: Global MHD simulations. Frontiers in Astronomy and Space Sciences, 9. p. 966164. ISSN 2296-987X

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The response of the Earth’s magnetotail current sheet to the external solar wind driver is highly time-dependent and asymmetric. For example, the current sheet twists in response to variations in the B y component of the interplanetary magnetic field (IMF), and is hinged by the dipole tilt. Understanding the timescales over which these asymmetries manifest is of particular importance during geomagnetic storms when the dynamics of the tail control substorm activity. To investigate this, we use the Gorgon MHD model to simulate a geomagnetic storm which commenced on 3 May 2014, and was host to multiple B y and B z reversals and a prolonged period of southward IMF driving. We find that the twisting of the current sheet is well-correlated to IMF B y throughout the event, with the angle of rotation increasing linearly with downtail distance and being more pronounced when the tail contains less open flux. During periods of southward IMF the twisting of the central current sheet responds most strongly at a timelag of ∼ 100 min for distances beyond 20 R E , consistent with the 1–2 h convection timescale identified in the open flux content. Under predominantly northward IMF the response of the twisting is bimodal, with the strongest correlations between 15 and 40 R E downtail being at a shorter timescale of ∼ 30 min consistent with that estimated for induced B y due to wave propagation, compared to a longer timescale of ∼ 3 h further downtail again attributed to convection. This indicates that asymmetries in the magnetotail communicated by IMF B y are influenced mostly by global convection during strong solar wind driving, but that more prompt induced B y effects can dominate in the near-Earth tail and during periods of weaker driving. These results provide new insight into the characteristic timescales of solar wind-magnetosphere-ionosphere coupling.

Item Type: Article
Additional Information: Funding information: JWBE was supported by Science and Technology Facilities Council (STFC) Studentship ST/R504816/1. JCC was supported by STFC Ernest Rutherford Fellowship ST/V004883/1. RS was supported by Natural Environment Research Council (NERC) grants NE/V002716/1 and NE/V002732/1. JWBE, LM, JPC and JPE acknowledge funding by NERC grant NE/P017142/1. JWBE, JPC andJPEacknowledge funding by NERCgrant NE/V003070/ 1. RD, JPC and JPE acknowledge funding by NERC grant NE/ P017347/1.
Uncontrolled Keywords: magnetotail twisting, current sheet, response timescales, geomagnetic storm, magnetosphere-ionophere coupling, global MHD simulations, space weather
Subjects: F500 Astronomy
Department: Faculties > Engineering and Environment > Mathematics, Physics and Electrical Engineering
Depositing User: John Coen
Date Deposited: 21 Sep 2022 10:28
Last Modified: 21 Sep 2022 10:30

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