Similarity and difference of Alfvén waves' propagation and evolution in the slow and fast solar wind of inner heliosphere

<div>Parker Solar Probe detected the Alfv&#233;nic slow solar wind in the inner heliosphere. Before that, although different spacecraft had measured that slow solar wind sometimes has Alfv&#233;nic characteristics, they did not attract extensive and strong attention and discussion. The critical question is, how does the propagation and evolution of Alfv&#233;nic waves perform through the same or different processes in the fast and slow solar wind? To study this problem, we simulate the formation of high and low-speed solar wind and the propagation of evolving Alfv&#233;n waves therein from a global perspective. Compared with one-dimensional or multi-dimensional simulations with a limited range of latitude and longitude, the advantage of global simulation is that it provides a self-consistent model of fast and slow solar wind coexisting in different flow tubes. Based on this model, we study and evaluate the effects of the expansion, bending, and non-uniformity across the flux tube on the propagation of evolving Alfv&#233;n wave. The varying characteristics during the propagation consist of wave amplitude, wave-vector anisotropy, wave mode conversion, etc. As the critical interface to distinguish the sub-Alfv&#233;nic and super-Alfv&#233;nic solar wind, which is also the vital interface to distinguish the corona and interplanetary space, Alfv&#233;n surface is another important aspect of our research. We study the propagation characteristics of Alfv&#233;n waves inside and outside the non-spherical interface. In addition, we also discuss the possible relationship between the propagation and evolution of the Alfv&#233;n wave and the formation and development of switchback.</div>