Self-Similar Outflows at the Source of the Fast Solar Wind: A Smoking Gun of Multiscale Impulsive Reconnection?

TL;DR

This study analyzes structured plasma outflows from the polar coronal hole, revealing self-similar, impulsive reconnection-driven events that significantly contribute to the fast solar wind's mass and energy fluxes.

Contribution

It provides the first evidence that polar coronal-hole outflows follow power-law distributions indicative of impulsive magnetic reconnection, linking small-scale dynamics to the fast solar wind.

Findings

Over 2300 plasma flow episodes identified in 6 hours.

Flow speeds are comparable to local sound speed (~122 km/s).

Outflows follow power-law distributions characteristic of impulsive reconnection.

Abstract

We present results of a quantitative analysis of structured plasma outflows above a polar coronal hole observed by the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory spacecraft. In a 6-hour interval of continuous high-cadence SDO/AIA images, we identified more than 2300 episodes of small-scale plasma flows in the polar corona. The mean upward flow speed measured by the surfing transform technique (Uritsky et al., 2013) is estimated to be 122 $\pm$ 34 \kms, which is comparable to the local sound speed. The typical recurrence period of the flow episodes is 10 to 30 minutes, and the mean duration and transverse size of each episode are about 3-5 min and 3-4 Mm, respectively. The largest identifiable episodes last for tens of minutes and reach widths up to $40$ Mm. For the first time, we demonstrate that the polar coronal-hole outflows obey a family of power-law probability distributions characteristic of impulsive interchange magnetic reconnection. Turbulent photospheric driving may play a crucial role in releasing magnetically confined plasma onto open field. The estimated occurrence rate of the detected self-similar coronal outflows is sufficient for them to make a dominant contribution to the fast-wind mass and energy fluxes and to account for the wind's small-scale structure.