Speaker
Description
The winding angle of the heliospheric magnetic field (HMF) is investigated by analyzing approximately 60 years of in situ spacecraft observations of the solar wind and the HMF at Earth. Yearly averages of the winding angle of the Low-Resolution OMNI (LRO) dataset, hosted on the NASA OMNIWeb website, are calculated taking into consideration the sector structure of the magnetic field measurements. The Lomb-Scargle periodogram is employed as a statistical method to determine whether the yearly averaged results show a dependence on the 11-year solar cycle. The results of previous analyses of the winding angle defined by the Parker model of the HMF at Earth are reproduced within reasonable agreement, after which the analysis is extended to the full LRO dataset for the case of a two-dimensional (2D) winding angle, and a three-dimensional (3D) model of the winding angle. In general, the 2D winding angle was found to be overwound from the average value predicted by the Parker model and to a similar degree as reported by previous studies, while also showing a statistically significant dependence on the solar cycle. The 3D winding angle was found to be underwound from the average value predicted by the Parker model, with no statistically significant dependence on the solar cycle. The underwound result of the 3D HMF can, in principle, be explained by a simple model of the HMF that accounts for the influence of turbulent fluctuations transverse to the Parker HMF that yields similar deviations from the winding angles predicted by the Parker HMF as those of the 3D winding angle model.
