On the Collisionless Asymmetric Magnetic Reconnection Rate

Area of Science:

• Space Physics
• Plasma Physics
• Astrophysics

Background:

• Understanding magnetic reconnection is crucial for space and astrophysical plasma evolution.
• Previous models for asymmetric reconnection had a free parameter for the diffusion region's aspect ratio.

Purpose of the Study:

• To predict the steady state reconnection electric field in asymmetric magnetic reconnection.
• To investigate the origin of the nearly universal reconnection rate of 0.1.

Main Methods:

• Maximizing the reconnection rate as a function of the upstream magnetic field's opening angle.
• Comparing predictions with existing asymmetric reconnection models in the collisionless limit.

Main Results:

• The prediction for the reconnection electric field is within a factor of 2 of the Cassak & Shay (2007) model.
• The new model has no free parameters, unlike previous ones.
• The normalized reconnection rate of 0.1 arises from maximizing the rate within magnetohydrodynamic constraints.

Conclusions:

• The nearly universal reconnection rate of 0.1 in asymmetric geometry is the maximal rate allowed at the magnetohydrodynamic scale.
• This finding has implications for transport processes at plasma boundaries, such as Earth's magnetopause.