Time‐Varying Magnetopause Reconnection During Sudden Commencement: Global MHD Simulations

In response to a solar wind dynamic pressure enhancement, the compression of the magnetosphere generates strong ionospheric signatures and a sharp variation in the ground magnetic field, termed sudden commencement (SC). While such compressions have also been associated with a contraction of the iono...

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Bibliographic Details
Published in:Journal of geophysical research. Space physics 2022-04, Vol.127 (4), p.n/a
Main Authors: Eggington, J. W. B., Desai, R. T., Mejnertsen, L., Chittenden, J. P., Eastwood, J. P.
Format: Article
Language:English
Subjects:
Atmospheric models
Compressive strength
Coupling
Dynamic pressure
dynamic pressure enhancement
Fluid flow
global magnetosphere simulations
Interplanetary magnetic field
interplanetary shock
ionospheric polar cap
Magnetic fields
Magnetic reconnection
Magnetohydrodynamics
Magnetopause
Magnetopause reconnection
Magnetosheath
Magnetospheres
Magnetotails
Parameter identification
Polar caps
Signatures
Simulation
Solar wind
Space weather
sudden commencement
Time dependence
Upper atmosphere
Weather
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Summary:In response to a solar wind dynamic pressure enhancement, the compression of the magnetosphere generates strong ionospheric signatures and a sharp variation in the ground magnetic field, termed sudden commencement (SC). While such compressions have also been associated with a contraction of the ionospheric polar cap due to the triggering of reconnection in the magnetotail, the effect of any changes in dayside reconnection is less clear and is a key component in fully understanding the system response. In this study, we explore the time‐dependent nature of dayside coupling during SC by performing global simulations using the Gorgon magnetohydrodynamic code and impact the magnetosphere with a series of interplanetary shocks with different parameters. We identify the location and evolution of the reconnection region in each case as the shock propagates through the magnetosphere, finding strong enhancement in the dayside reconnection rate and prompt expansion of the dayside polar cap prior to the eventual triggering of tail reconnection. This effect pervades for a variety of interplanetary magnetic field orientations, and the reconnection rate is most enhanced for events with higher dynamic pressure. We explain this by repeating the simulations with a large explicit resistivity, showing that compression of the magnetosheath plasma near the propagating shock front allows for reconnection of much greater intensity and at different locations on the dayside magnetopause than during typical solar wind conditions. The results indicate that the dynamic behavior of dayside coupling may render steady models of reconnection inaccurate during the onset of a severe space weather event. Plain Language Summary The Earth’s magnetic field is often impacted by strong impulses of magnetized plasma ejected from the Sun. These compress the boundaries of the region shielded by the magnetic field and generate sudden signatures in the upper atmosphere and on the ground which can have societal effects. During the compression, some mass and energy is able to penetrate this shield more effectively than usual through a process called magnetic reconnection. We perform computer simulations of several such compressions to explore the effect on reconnection in detail, quantifying its enhancement and the dependence on various parameters. We find that reconnection is intensified immediately at the point of compression and undergoes a highly time‐dependent behavior for several minutes after im
ISSN:2169-9380
2169-9402
DOI:10.1029/2021JA030006