Polar jet streams are super powerful and very focused wind bands that just wrap around the planet. They're like walking on a moving sidewalk in an airport, yes, but one that goes 200 miles an hour. The reason the jet stream is so powerful up northof the polar jet stream is because the difference in temperature between the polar cell in the farel cell is much different. It can't go all the way down because the pull of the coreolis effect is such that it stretches it out into a stream. That's what happens member when we get a polar vortex every once in a while.