Super-Alfv\'enic propagation of reconnection signatures and Poynting flux during substorms

TL;DR

This study reveals that reconnection signatures in Earth's magnetotail propagate super-Alfvénically as kinetic Alfvén waves, producing significant Poynting flux capable of powering auroras, based on simulations and satellite data.

Contribution

It demonstrates that reconnection signatures propagate as super-Alfvénic kinetic Alfvén waves, a novel insight supported by simulations and satellite observations.

Findings

Reconnection signatures propagate as super-Alfvénic kinetic Alfvén waves.

Generated Poynting flux is sufficient to power Earth's auroras.

Satellite observations confirm the wave propagation and energy flux estimates.

Abstract

The propagation of reconnection signatures and their associated energy are examined using kinetic particle-in-cell simulations and Cluster satellite observations. It is found that the quadrupolar out-of-plane magnetic field near the separatrices is associated with a kinetic Alfv\'en wave. For magnetotail parameters, the parallel propagation of this wave is super-Alfv\'enic (V_parallel ~ 1500 - 5500 km/s) and generates substantial Poynting flux (S ~ 10^-5 - 10^-4 W/m^2) consistent with Cluster observations of magnetic reconnection. This Poynting flux substantially exceeds that due to frozen-in ion bulk outflows and is sufficient to generate white light aurora in the Earth's ionosphere.