Three‐Dimensional Magnetic Reconnection Spreading in Current Sheets of Non‐Uniform Thickness

Journal Article · 15 March 2023 · Journal of Geophysical Research. Space Physics

DOI: https://doi.org/10.1029/2022JA030999 · OSTI ID:1961928

Arencibia, Milton  ^[1]; Cassak, Paul A.  ^[1]; Shay, Michael A.  ^[2]; Qiu, Jiong  ^[3]; Petrinec, Steven M.  ^[4]; Liang, Haoming  ^[5]

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1. Department of Physics and Astronomy and Center for KINETIC Plasma Physics West Virginia University Morgantown WV USA
2. Department of Physics and Astronomy University of Delaware Newark DE USA
3. Department of Physics Montana State University Bozeman MT USA
4. Lockheed Martin Advanced Technology Center Palo Alto CA USA
5. Center for Space Plasma and Aeronomic Research (CSPAR) University of Alabama in Huntsville Huntsville AL USA

Abstract Magnetic reconnection in naturally occurring and laboratory settings often begins locally and elongates, or spreads, in the direction perpendicular to the plane of reconnection. Previous work has largely focused on current sheets with a uniform thickness, for which the predicted spreading speed for anti‐parallel reconnection is the local speed of the current carriers. We derive a scaling theory of three‐dimensional (3D) spreading of collisionless anti‐parallel reconnection in a current sheet with its thickness varying in the out‐of‐plane direction, both for spreading from a thinner to thicker region and a thicker to thinner region. We derive an expression for calculating the time it takes for spreading to occur for a current sheet with a given profile of its thickness. A key result is that when reconnection spreads from a thinner to a thicker region, the spreading speed in the thicker region is slower than both the Alfvén speed and the speed of the local current carriers by a factor of the ratio of thin to thick current sheet thicknesses. This is important because magnetospheric and solar observations have previously measured the spreading speed to be slower than previously predicted, so the present mechanism might explain this feature. We confirm the theory via a parametric study using 3D two‐fluid numerical simulations. We use the prediction to calculate the time scale for reconnection spreading in Earth's magnetotail during geomagnetic activity. The results are also potentially important for understanding reconnection spreading in solar flares and the dayside magnetopause of Earth and other planets.

• Research Organization: West Virginia Univ., Morgantown, WV (United States)
• Sponsoring Organization: NASA; National Science Foundation (NSF); USDOE; USDOE Office of Science (SC)
• Grant/Contract Number: AC02-05CH11231; SC0020294
• OSTI ID: 1961928
• Journal Information: Journal of Geophysical Research. Space Physics, Journal Name: Journal of Geophysical Research. Space Physics Journal Issue: 3 Vol. 128; ISSN 2169-9380
• Publisher: American Geophysical Union (AGU)Copyright Statement
• Country of Publication: United States
• Language: English