I’ve been struggling with coming up with an analogy that might help people visualize the effect the jet stream has. It can be a little difficult to understand how it functions, partly because it is three dimensional and constantly changing.
I might have come up with something that will help, though it might not help much for people who don’t know much about boats and water or who have never experienced either, but I’m going to give it a try.
The question many people have is how a current of air that is 6-9 miles off the ground and which is relatively small, a few hundred miles wide and a quarter of a mile thick, can impact the weather on the ground as much as the jet stream does. Something similar can be seen with boats and ships moving over a lake or the ocean.
When a ship moves through the water, it creates a bow wave because water doesn’t compress. The larger the boat/ship and the greater the speed, the bigger the bow wave is. Some US Navy ships can achieve a speed of close to 50 mph, such as cutters and destroyers. While these ships are much larger than an 11-foot aluminum rowboat, they are small as compared to vessels like supertankers. In a like way, a supertanker is tiny compared to the oceans it travels.
Still, the bow wave that a cutter moving at 50 mph makes is substantial. If you see it from the deck or in a movie, it appears as water that is pushed up right in front of the bow of the ship and then peels off to either side. What you don’t see is the turbulence it causes below the bow wave and below the ship. The cutter is actually disturbing the water dozens of feet below the ship because the bow wave makes the water pile up and curl to each side. The disruption continues for a great distance before the water calms back down.
That part has been experienced by most people who’ve been standing on the shore of a lake or calm river when a fast-moving boat goes by. Even if the boat is several hundred feet away from the shore, many times farther from the shore than the boat is wide, the bow wave spreads out and on the shore, there are surging waves that splash up, generated by that bow wave. The boat can cause effects a great distance away.
In a similar way, a jet stream isn’t very large in comparison to the atmosphere at an altitude of 6-9 miles. However, it causes the air to pile up; and move out of the way. It has an impact that is felt a great distance away. Unlike the water analogy, though, most of the disturbance is focused downward because of the density of the air below the jet stream. The jet is also moving at a tremendous speed, relative to someone who is standing still.
The winds in the jet stream can move at up to 250 mph. For comparison, a category 5 hurricane has wind speeds of 157 mph. The jet stream can have winds that are almost a hundred miles per hour faster. Air is also far less dense than water, so the effects reach a lot farther. That bow wave that is created pushes the air to either side, all the way to the ground. If the air on one side is hot, it is stopped from mixing with the cooler air on the other side, which is also being pushed away.
Additionally, unlike a boat, the jet stream can be thousands of miles long in a continuous ribbon.
Thus, hot air tends to be kept to the south of the north circumpolar jet stream and colder air is normally kept north of it.
Does this analogy help visualize why the jet stream does what it does?
I’m not sure