Generation of Non-Propagating Alfvenic Double Layer and Formation of Alfvenic and Quasi-Static Discrete Auroras

English Abstract:

The nonlinear interaction of incident and reflected Alfven wave packets in auroral acceleration regions can collectively produce non-propagating electromagnetic plasma structures, such as Transverse Alfvenic Double Layers (TA-DL) and Charge Holes (TA-CH). These dynamic quasi-static cellular structures include localized strong electrostatic electric fields nested in low density cavities and surrounded by locally enhanced magnetic and velocity fields. The locally enhanced magnetic and velocity fields carrying the free energy act as a local dynamo, which can continuously sustain the generation of electrostatic electric fields for a meaningful time. During this process, the generated electrostatic electric fields will also deepen the low density cavity, which can further boost the generation of powerful electric fields. Auroral charged particles can be effectively accelerated by the TA-DL, which create both Alfvenic and quasi-static discrete auroras.

The dynamical theory of the generation of the electrostatic electric fields suggests that the formation of Alfvenic and quasi-static auroras should have a unified mechanism. In both cases, parallel electric fields are generated by Alfvenic interactions in the inhomogeneous M-I coupling system, rather than by diffusive or passive processes. The TA-DL carrying strong parallel electric fields is produced by the nonlinear interaction of Alfven wave packets while the Poynting flux, a major energy source for auroral formation, is carried by Alfven waves.