Abstract Periodic density structures (PDSs) are advecting quasi‐periodic (periodicities between several minutes and several hours) density enhancements observed in the solar wind and corona. There is strong evidence that PDSs are formed at the Sun. We report here an analysis of Ulysses data in which we identify PDSs using the multi‐taper method, representing the first of its kind in solar wind emanating from polar coronal holes (PCH) at high heliolatitude. Probability distributions of identified frequencies are very similar in both PCH wind and non‐PCH wind; they resemble the distribution of frequencies derived from recent analysis of Wind data (Kepko et al., 2024, https://doi.org/10.1029/2023ja031403 ). All resemble the distribution of transverse fluctuations in the corona. These results demonstrate that the source of PDSs is globally distributed. The large number of alpha‐to‐proton PDSs found indicate that PDSs originate in the low corona, where the alpha‐to‐proton ratio is set. Analyzing PDSs as a function of distance from the Sun, we found that their occurrence rate is generally decreasing, which supports the hypothesis that PDSs have a solar source and a processing en route gradually diminishes their coherence. In the ratio of the frequency distributions of protons and the alpha‐to‐proton density ratio, we found enhancements for non‐PCH wind at 0.3 mHz and for PCH wind at 0.4 mHz. Similarly, we calculated the occurrence distribution of instantaneous radial length scales and found that the slow wind (550 km ) peaked at 800 Mm, while the fast wind peaked at 1,000 Mm, suggesting some characteristics of PDSs depend on the magnetic field at their solar source.
Randol et al. (Sun,) studied this question.