# An Analogy to Gain a Better Understanding of a Jet Stream

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?

• Yes
• No
• I’m not sure

12 points

## Written by Rex Trulove

1. A very informative post, as always Rex. I learned a lot here.

• That is a very good thing. I’m glad if it taught something.

2. Thank you for making the jet stream concept even clearer.

• I am quite happy if it did so. Thank you for the confirmation.

3. Nicely done! It also speaks to the reality of why the Jet Stream is so impactful. The reality of air moving 3, 4 and 5 times faster higher, wider and with more power changes things.

I would use the analogy of your 11-foot rowboat, crossing the wake of a supertanker. If, the rowboat makes it to the other side, Highly unlikely that they would. The first 6-10 foot wake would probably make them reconsider doing that again.

In the Bay, the USCS arrests PWC drivers that cut behind large ships. Why? Because so many people did the first jump and the watercraft and they were separated.

• I can understand that. Many smaller vessels are capsized every year for exactly that reason. People can also easily drown from being sucked under by the undertow that is created.

The amount of power contained in the jet stream is hard for most folks to imagine. Saying that the wind speed can be up to 250 mph lacks meaning because that is just a number. Explaining that this is almost 100 mph faster than the winds of the strongest hurricanes puts it into perspective, though.

The power of the jet stream is very similar to the power in a tornado. Sadly, even pointing that out doesn’t necessarily shed any clarity because a lot of people have neven seen the damage that is done by a tornado, particularly when it is occurring.

I might write about tornadoes next, mostly to demonstrate the power they have.

• I remember once flying to Tokoyo, I had a 5-hour connection window, that I thought was stupidly huge.

We flew into the jet stream – or as the pilot called it a slight headwind.

we were 3 hours late. By the time I cleared customers in Narita, I had 12 minutes to make it to the gate for my next flight.

4. Jet streams usually form in the winter, when there is a greater contrast in temperature between cold continental air masses and warm oceanic air masses

• Our jet streams are there all year long. The biggest seasonal difference for the circumpolar jet stream is where it is located. As the land in the continental US heats up in the summer, the jet stream usually moves northward. In the winter, it moves farther south.

One thing that has an effect, too, is the are coming in off the Gulf of Alaska. That air can move in any direction, but if it comes in off the ocean and moves to the east or slightly north of east, the jet stream is usually very strong and the effects are much more pronounced. There is also often more moisture brought in. Still, this can happen at any time of the year.

5. Thank you that was very helpful and informative. If I am correct then it has to do with the jet stream when I see the water get choppier even before the boat had come in sight.

• It can have to do with that if the boat is displacing a lot of water and particularly if it isn’t moving very fast. In that case, the boat is pushing the water ahead, more than it is pushing it to the sides.