Mode conversion and wave -particle interaction processes in the solar wind

This thesis presents the theoretical study of wave coupling and wave-particle interaction processes in the solar corona and wind. We first investigate the effect of an inhomogeneous velocity field on the propagation of waves in the solar atmosphere. We find that coupling between Alfven waves and fast magnetosonic waves can occur for parameters characterizing the coronal holes. For streamer conditions, the Alfven wave couples to the slow magnetosonic mode. In the inner corona, it seems that these two possible ways of coupling do not occur simultaneously in the same structures, while beyond 5--10 R⊙ , where the plasma beta is about unity, both of them can operate at the same time and the mechanism gets more sensitive to the background plasma conditions. The second part of the thesis extends the findings to determine the trajectory of waves once they undergo much of the transformation. We then examine the propagation of fast magnetosonic waves from the Sun\u27s lower atmosphere to the corona. The background in which the launched wave propagates corresponds to the region from the photosphere to the low corona, where the Alfven speed undergoes drastic changes. We find that the frequency shift of the local wave frequency due to the background flow is not significant enough to move very low frequency waves to the high frequencies needed to resonate with ions. A likely result of wave dissipation is the heating and acceleration of the solar coronal particles. The third part of the thesis examines a specific wave-particle interaction in the solar wind. Observational data show that alphas ( He2+4 ) and other ions in the interplanetary medium have a tendency to stream near or below the local Alfven speed (VA ) relative to the main component of protons. To understand the details of the wave-particle interaction process, we have performed hybrid simulations for a plasma, which consists of protons, alphas and massless quasineutralizing electrons. In an initial phase, the protons are at rest while alphas are streaming at a given speed. In this medium, Alfven waves are launched initially and our aim is to follow how the system develops in time when all the nonlinear forces involved in the process are considered. The simulated result is that the streaming population of alphas generally decelerates towards the speed of the protons. The streaming energy of alphas goes to their thermal energy. The predicted evolution of the bulk properties of alphas is fairly consistent with solar wind observations