Electromagnetic viscosity supported anomalous electric field in the electron diffusion region of collisionless magnetic reconnection

Abstract Summary

Kinetic-scale electromagnetic fluctuations often appear in the reconnection electron diffusion region, potentially accelerating processes through anomalous effects. These fluctuations mainly contribute via the electromagnetic anomalous viscosity term $${{{\boldsymbol{T}}}}_{{{\mathrm{EM}}}}=-{\frac{ < \delta (n{{\bf{V}}})\times \delta {{\bf{B}}} > }{ < n > }}$$. The maximum anomalous viscosity can reach up to ~20% of the fast reconnection electric field, though typically less.

Key Findings

Total anomalous electric field $$ R_M $$ peaks at ~0.025 mV/m inside the electron diffusion region (EDR), aligning with the out-of-plane reconnection field but comprising only 3% of it (Table 1).
In EDR 10, $$ R_M $$ hits ~0.036 mV/m (~1% of reconnection field) at the center, with negative values at edges; fluctuations occur both inside and outside EDR.
Across events, EM fluctuations yield positive $$ RM $$ in +M direction, supporting reconnection; ratio $$ P = {R}{M,\max} / < {E'}_{M,\max} > $$ quantifies this (Table 1, Column 7).

Contributions to Anomalous Fields

Anomalous electric fields in EDR primarily stem from EM viscosity $$ T_{EM,M} $$ (correlation r ≈ 0.98), not anomalous drag $$ DM $$ or electrostatic viscosity $$ T{ES,M} $$. Data cluster around $$ {R}{M}/{|{R}{M}|}{\max }={T}{{EM}}/{|{R}{M}|}{\max } $$, confirming dominance. Drag and ES viscosity mutually restrain each other, akin to effects in asymmetric reconnection where electrons stay nearly frozen-in.

Electromagnetic fluctuations provide anomalous effects in EDRs mainly through EM anomalous viscosity, supporting up to 20% of the reconnection electric field at peak.

Author's Summary: This study reveals electromagnetic anomalous viscosity as the key driver of supportive electric fields in collisionless reconnection's electron diffusion region, contributing up to 20% of the reconnection field based on spacecraft data analysis (148 characters).

Nature — 2025-11-27

Abstract Summary

Key Findings

Contributions to Anomalous Fields

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