Observations of Transition from Imbalanced to Balanced Kinetic Alfv\'enic Turbulence

TL;DR

This paper presents solar wind observations showing a transition from imbalanced to balanced kinetic Alfvénic turbulence, marked by changing magnetic helicity ratios and wave signatures, providing new insights into turbulence dynamics.

Contribution

It provides the first observational evidence of the transition from imbalanced to balanced kinetic Alfvénic turbulence in the solar wind.

Findings

Magnetic helicity emerges in the turbulence transition range.

The ratio of opposing sign KAWs increases then decreases during transition.

First direct evidence of imbalanced to balanced KAW turbulence transition.

Abstract

We report observations of solar wind turbulence derived from measurements by the Parker Solar Probe. Our findings reveal the emergence of finite magnetic helicity within the transition range of the turbulence, aligning with signatures of kinetic Alfv\'en waves (KAWs). Notably, as the wave scale transitions from super-ion to sub-ion scales, the ratio of KAWs with opposing signs of magnetic helicity initially increases from approximately 1 to 6.5 before returning to 1. This observation provides, for the first time, compelling evidence for the transition from imbalanced kinetic Alfv\'enic turbulence to balanced kinetic Alfv\'enic turbulence.