Recent observations have revealed the ubiquitous presence of small-scale inhomogeneities in the solar wind, which are important for solar wind energy transport and defining its characteristic variability. In this thesis, we investigate Alfvén wave trapping between imposed density enhancements and the creation of propagating periodic density fluctuations. Alfvén waves are important carriers of magnetic energy, whose opportunities for dissipation can be increased by continuous reflections from field-aligned density inhomogeneities. In the first study, we confirm that specific length scales are required for optimal wave trapping. This can be understood in terms of wave interference, which is more pronounced for an extended medium with equally-spaced density inhomogeneities. Further, we investigate magnetohydrodynamic (MHD) wave-driven formation of periodic density fluctuations in the solar wind above a helmet streamer. Density fluctuations – generated from either Alfvén or slow and fast magnetoacoustic waves – exhibit qualitatively similar propagation. In a low 𝛽 plasma, the dominant contribution to the density fluctuations comes from the slow mode, while in a high 𝛽 plasma, both slow and fast modes have significant contributions. Despite this similarity, density fluctuations produced from Alfvén waves have a doubled frequency with respect to the driven waves, whereas magnetoacoustic waves produce density fluctuations with the same frequency. The inclusion of a pseudo-streamer into this model enables us to compare the propagation of MHD waves and density fluctuations in different magnetic topologies. Key differences in their propagation are in terms of wave interference, presence of a null point and structure of the high 𝛽 region. For example, along the pseudo-streamer axis, only fast waves contribute to the density fluctuations, despite being in a low 𝛽 plasma, unlike the helmet streamer axis. However, observational signatures of the density fluctuations remain largely similar for the pseudo-streamer and the helmet streamer, consistent with recent white light observations.
Anmol Kumar (Tue,) studied this question.