New Insights into Solar Wind Fluctuations Challenge Existing Theories

Recent research utilizing data from the Parker Solar Probe has revealed significant findings regarding the behavior of solar wind fluctuations. The study, titled "Observed Fluctuation Enhancement and Departure from WKB Theory in Sub-Alfvénic Solar Wind," was conducted by David Ruffolo and 14 co-authors. It focuses on the fluctuation amplitudes in the solar wind as it transitions from sub-Alfvénic to super-Alfvénic speeds.

The researchers found that, contrary to the predictions of the Wentzel-Kramers-Brillouin (WKB) theory, the magnetic and kinetic fluctuation energies per unit volume do not decrease monotonically as expected. Instead, there is a clear violation of the conservation of standard WKB wave action. This suggests that there is a significant input of fluctuation energy in the solar wind near the Alfvén critical region, which may be driven by large-scale coronal shear flows.

These findings have implications for our understanding of solar wind dynamics and the mechanisms that govern energy transfer in the solar atmosphere. The results challenge existing theoretical frameworks and highlight the complexity of solar wind behavior, particularly in regions where the flow speed approaches the Alfvén wave speed. This research could lead to a reevaluation of models used to predict solar wind characteristics and their effects on space weather phenomena.

The full paper can be cited as follows: Ruffolo, D., Thepthong, P., Pongkitiwanichakul, P., Roy, S., Pecora, F., Bandyopadhyay, R., Chhiber, R., Usmanov, A. V., Stevens, M., Badman, S., Romeo, O., Wang, J., Goodwill, J., Goldstein, M. L., Matthaeus, W. H. (2024). Observed Fluctuation Enhancement and Departure from WKB Theory in Sub-Alfvénic Solar Wind. arXiv:2409.02612.