Scaling laws for magnetic reconnection, set by regulation of the electron pressure anisotropy to the firehose threshold. Issue 24 (31st December 2015)

• Record Type: Journal Article
• Authors: Ohia, O.; Egedal, J.; Lukin, V. S.; Daughton, W.; Le, A.
• Is Part Of: Geophysical research letters. Volume 42:Issue 24(2015:Dec.)
• Page Start: 10, 549
• Page End: 10, 556
• Publication Date: 2015-12-31
• Subjects: magnetic reconnection -- electron anisotropy -- electron energization -- plasma simulation; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1002/2015GL067117
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Magnetic reconnection in a weakly collisional plasma, such as in the Earth's magnetosphere, is known to be accompanied by electron pressure anisotropy. For reconnection scenarios including moderate guide magnetic field, electrons are magnetized throughout the reconnection region, and the anisotropy drives extended electron current layers. Along these layers, the anisotropy nears the firehose threshold. We describe how the anisotropy stagnates at this threshold by a mechanism that does not involve pitch‐angle mixing. Using previously established anisotropic equations of state and by imposing the marginal firehose condition, scaling laws are obtained for quantities along the current layers as functions of plasma parameters upstream of the reconnection region. The predicted reconnection region quantities include the magnetic field strength, plasma density, and the parallel and perpendicular electron pressures, allowing for a characterization of electron energization solely as a function of the upstream plasma conditions. This characterization is in agreement with simulations and spacecraft observations. Key Points: Electron pressure anisotropy can drive currents that negatively feedback on the pressure anisotropy Predictive scaling has been derived for moderate component collisionless reconnection Anisotropic electron energization in these current layers can be inferred from upstream conditions