Alfvén waves: Unresolved issues Original Research Article

Different aspects of Alfvén waves have been investigated for decades. In this paper we first present what we know about these waves from knowledge gained from these studies along with their limitations. We then point out some of the unresolved issues related to these waves with an emphasis on some intriguing observations that have not been properly explained so far. Some suggestions, about improving the existing models or making new quantitative models for the interpretation of these observations, are presented.