According to NOAA: “Colder temperatures to the north and warmer temperatures to the south create winds that generally blow from west to east around the northern hemisphere. This atmospheric river of strong winds can vary from a straight west-to-east pattern, to a more wavy pattern.
Does climate change influence the polar vortex? In short, yes. For a lucid explanation, you cannot do better than John Holdren. Holdren is a distinguished scientist who serves as Director of the White House Office of Science and Technology Policy. See the video from Holdren. (HT to ICN.) (If you want an even more in-depth explanation, see this from Climate Central.)