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The dynamic evolution of a coronal mass ejection (CME) in the interplanetary space generates a highly turbulent, compressed, and heated shock-sheath. This region provides an exceptional setting for investigating the intricate fluctuations occurring at small scales and offers a valuable opportunity to unravel the underlying physical processes responsible for turbulence dissipation and plasma heating. Understanding the role of turbulence in controlling the energy transport process in a magnetized plasma, within space and astrophysics, remains an enticing challenge of the twenty-first century. In this article, we study sheath regions observed by the Wind spacecraft from 1995 to 2021. We find 80 sheath events out of the studied 384 events that show a significant Alfvénic nature (≈21%). These fluctuations are interpreted as Alfvénic wave packets propagating either parallel or antiparallel to the background magnetic field, quantified by the normalized crosshelicity ( σ C ). We find 47 sheath events with outward-propagating Alfvénic fluctuations and 33 events with inward Alfvénic characteristics. The Alfvénic sheaths had a mean value of σ C = 0.46 ± 0.03 and − 0.43 ± 0.02 for outward- and inward-directed Alfvénic sheaths, respectively. Furthermore, we compare the average interplanetary parameter values of both the Alfvénic sheaths and the ambient solar wind. The study has strong implications in the domain of interplanetary space plasmas, its interaction with planetary plasmas, and astrophysical plasmas. [ABSTRACT FROM AUTHOR]

The polytropic behavior describes the relationship between macroscopic properties of plasma species and provides useful information in understanding physical mechanisms in space plasma. Through the value of the polytropic index, which governs the polytropic relationship, we can identify the energy transfer in plasma systems. In this paper, we determine the polytropic index of proton plasma within an Interplanetary Coronal Mass Ejection (ICME), which has been observed by three different spacecraft at ∼ 1 AU, each separated by ∼ 20 ∘ degrees in longitude during the analyzed observations. By performing this multi-spacecraft analysis, we provide evidence that the polytropic index does not vary significantly across the structure of the observed ICME. This may imply that the ICME evolution process is nearly coherent. Moreover, the polytropic index values we derive here can set boundary conditions in existing and future ICME evolution models. [ABSTRACT FROM AUTHOR]

Interplanetary coronal mass ejections (ICME) are large-scale eruptions from the Sun and prominent drivers of space weather disturbances, especially intense/extreme geomagnetic storms. Recent studies by our group showed that ICME sheaths and/or magnetic clouds (MC) could be transformed into a planar magnetic structure (PMS) and speculate that these structures might be more geo-effective. Thus, we statistically investigated the geo-effectiveness of planar and non-planar ICME sheaths and MC regions. We analyzed 420 ICME events observed from 1998 to 2017, and we found that the number of intense ( − 100 to − 200 nT) and extreme (< − 200 nT) geomagnetic storms are large during planar ICMEs (almost double) compared to non-planar ICMEs. In fact, almost all the extreme storm events occur during PMS molded ICME crossover. The observations suggest that planar structures are more geo-effective than non-planar structures. Thus, the current study helps us to understand the energy transfer mechanism from the ICME/solar wind into the magnetosphere, and space-weather events. [ABSTRACT FROM AUTHOR]