Negative and Positive Cascade Rates of Slow Alfvénic Turbulence in Switchback and Nonswitchback Intervals: Wind Observations

Abstract

Abstract We estimate the turbulent cascade rate in imbalanced Alfvénic turbulence in the slow solar wind using a Politano–Pouquet-based approach that does not require an isotropic assumption. We analyze selected 8 hr intervals provided by the Wind spacecraft. These intervals are characterized by near-homogeneity, weak velocity shear, and imbalanced Alfvénic fluctuations, and are classified as switchback or nonswitchback depending on the angular spread of the magnetic field relative to the mean field. Switchback intervals are identified by large magnetic-field rotations, whereas nonswitchback intervals exhibit only small angular deviations. Our results show that nonswitchback intervals exhibit a positive total cascade rate and power spectra consistent with a −3/2 scaling, indicative of a forward energy cascade. In contrast, switchback intervals are characterized by a negative total cascade rate, and by steeper power spectra with a spectral index of approximately −1.6. This indicates that large magnetic-field rotations can substantially modify the scale-to-scale energy transfer in Alfvénic slow solar wind. The results suggest that switchbacks may be associated with additional physical processes, such as local instabilities or reconnection-related structures, that alter the direction and magnitude of the turbulent cascade. These findings may help explain previous reports of negative cascade rates in imbalanced Alfvénic solar-wind turbulence.