Particle simulations of magnetotail dynamics guided by empirical reconstruction of substorms with data-mining algorithms: Steady and unsteady reconnection regimes
Abstract
Empirical reconstruction of the magnetotail during substorms by means of data mining provides an unprecedentedly detailed picture of its structure and dynamics that can be used to guide its kinetic simulations. It reveals in particular two regions with distinctly different regimes of magnetic reconnection. While the reconnection process near the mid-tail X-line (-30 RE) is steady, another reconnection process near a transient flux rope closer to Earth (x>-20 RE) is unsteady, which is seen and quantitatively evaluated from the changing magnetic field there. It also shows that the substorm dipolarization is preceded by the formation of a flux accumulation regions between -30 and -20 RE. This empirical picture is used in 3-D PIC simulations of weakly driven magnetotail equilibria with a flux accumulation area, similar to what is detected in the empirical reconstruction. Simulations show a similar combination of steady and unsteady reconnection regions. Near the more distant X-line, they show classical signatures of the steady reconnection regime, including the spatially homogeneous profile of the electric field in the meridional plane with the characteristic value corresponding to 0.1 reconnection rate, super-Alfvenic bulk flows and non-gyrotropic electron motions near the electron diffusion region. In contrast, the reconnection electric field in the unsteady region is localized in space around a dipolarization front and another X-line in its trail. Its peak value strongly exceeds the steady reconnection rate estimate. Simulations suggest that unsteady reconnection is supported by kinetic dissipation, consistent with MMS observations.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMSM027..07S
- Keywords:
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- 2723 Magnetic reconnection;
- MAGNETOSPHERIC PHYSICS;
- 7526 Magnetic reconnection;
- SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMY;
- 7835 Magnetic reconnection;
- SPACE PLASMA PHYSICS