Julia Ruohotie | Searcharxiv

arXiv2025

Intermittency in Interplanetary Coronal Mass Ejections Observed by Parker Solar Probe and Solar Orbiter

Intermittency has been studied extensively in the fast and slow solar winds but to a far lesser extent in interplanetary coronal mass ejections (ICMEs). While ICMEs are often characterized by their relatively smooth, large-scale magnetic flux rope structures, a spectrum of fluctuations is nonetheless present at smaller scales. We have examined kurtosis and its scaling exponents at magnetohydrodynamic inertial scales in 49 ICMEs observed between 0.25 and 1 au by Parker Solar Probe and Solar Orbiter, and compared the results to those obtained for the ICME sheath regions and ambient solar wind intervals. Kurtosis behaves similarly in all intervals studied and presents a universal behavior typical of intermittent time series. The ICMEs displayed a radially invariant level of intermittency, suggesting that they are relatively static, well-developed turbulent environments. In the sheath regions, the level of intermittency increased with distance, indicating that the turbulence is not yet fully developed at small heliocentric distances. In addition to intermittent fluctuations related to turbulence, the sheath regions may possess a population of non-turbulent structures that increase the absolute value of kurtosis.

astro-ph.SR↗

arXiv2025

Effect of interplanetary shock waves on turbulence parameters

We have performed an extensive statistical investigation of how interplanetary fast forward shocks affect certain turbulence parameters, namely, the cross-helicity, $σ_c$, residual energy, $σ_r$, and magnetic helicity, $σ_m$. A total of 371 shocks detected by Wind at 1 au and seven shocks by Solar Orbiter at 0.3-0.5 au have been analysed. We explore how the aforementioned turbulence parameters and their variation across the shock depend on shock characteristics including the gas compression ratio, upstream plasma beta, velocity jump and shock angle. In the shock vicinity, fluctuations tend on average to show antisunward imbalance (measured as $σ_c>0$ when rectified to the Parker spiral direction), a dominance of magnetic energy ($σ_r<0$) and zero $σ_m$, all being typical solar wind properties . Antisunward imbalance and equipartition ($σ_r \sim0$) in the upstream is increasingly prevalent with increasing shock velocity jump and decreasing upstream beta and shock angle. Shocks with large velocity jumps and gas compression ratios have considerably more balanced ($σ_c\sim0$) and more magnetically dominated fluctuations downstream than upstream. From upstream to downstream, we also find that the occurrence of time periods fulfilling strict criteria for Alfvénic fluctuations (AFs) usually decreases, while those meeting the criteria for small-scale flux ropes (SFRs) increases. The occurrence of AF periods peaks for quasi-parallel shocks with large velocity jumps and small upstream beta. The occurrence of SFRs increases with increasing gas compression ratio and upstream beta. The shocks observed by Solar Orbiter below 0.5 au display similar distributions of turbulence parameters and upstream-to-downstream changes to those detected at 1 au. These results are relevant for understanding turbulence and charged-particle acceleration at collisionless shocks.

astro-ph.SR↗