Cross-scale Correlations in Imbalanced Solar Wind Turbulence: Parker Solar Probe Observations

Based on Parker Solar Probe observations, this paper investigates the proton temperature, bulk speed, proton-scale magnetic helicity, and spectral index in the parameter space of (P ( I ), sigma ( c )), where P ( I ) is the magnetic energy density and sigma ( c ) is the normalized cross helicity at proton inertial scales. Various correlations between these parameters are discussed and their relations are explored. These correlations indicate the following: (1) the turbulence with a larger P ( I ) is characterized by a higher sigma ( c ); (2) a larger P ( I ) corresponds to a higher proton temperature, faster bulk speed, and steeper proton-scale magnetic spectrum; (3) a higher sigma ( c ) accounts for higher proton-scale magnetic helicity. In particular, the P ( I ) has the largest correlation coefficient (CC) of 0.85 with proton temperature and has a considerably large CC of 0.70 with a proton-scale spectral index. The sigma ( c ) has a moderate CC of 0.52 with magnetic helicity in the low beta ( p ) case (beta ( p ) < 0.6), where beta ( p ) is the ratio of plasma to magnetic pressure. The correlation between sigma ( c ) and P ( I ) is considerable with a CC exceeding 0.6 in the low beta ( p ) case and tends to be negligible when beta ( p ) approaches 1.5. These findings could be understood by the recently discovered helicity barrier effect and underline the importance of the generalized helicity invariant in low beta ( p ) collisionless plasma for understanding imbalanced solar wind turbulence.

Automated summary

This paper investigates correlations between proton temperature, bulk speed, proton-scale magnetic helicity, and spectral index based on Parker Solar Probe observations. The results show that there are positive correlations between magnetic energy density and proton temperature, bulk speed, and proton-scale magnetic spectrum. The paper also finds a moderate correlation between normalized cross helicity and magnetic helicity.