How Flying Works
Jet Streams: The World’s Real Rivers of Wind
In February 2020, a British Airways Boeing 747 flying from New York to London reached a ground speed of over 800mph. That’s nowhere near the speed of sound through the surrounding air, but it was real and measured, and it brought the flight in more than an hour early. The aircraft wasn’t flying unusually fast. It had climbed into an unusually strong jet stream, boosted that week by Storm Ciara, and let the atmosphere do part of the work. Jet streams are the main reason two flights on the same route, in opposite directions, almost never take the same time. And they’re real, mapped features of the atmosphere, not a loose term for “wind up high”.
What a jet stream actually is
A jet stream is a narrow, fast ribbon of wind, usually 4-8 miles above the ground. It forms where two air masses of very different temperature sit side by side. The bigger the temperature gap, the stronger the jet. That’s why jet streams strengthen in winter, when the gap between polar cold and warmer air further south is widest. A jet stream doesn’t run in a straight line around the planet. It snakes in broad, slow loops called Rossby waves, dipping towards the equator in one place and towards the pole in another. So its exact position shifts week to week, even though the band of latitude it lives in stays roughly the same.
There are four major jet streams — and a fifth that runs backwards
Each hemisphere has two: a polar jet at about 50-60° latitude, and a subtropical jet nearer the equator at about 30°. That makes four major jet streams circling the planet, all flowing broadly west to east. The Northern Hemisphere polar jet matters most for flights across the Atlantic and Pacific, because it runs right across the North America–Europe and North America–Asia routes most airline traffic uses. The Southern Hemisphere polar jet circles almost entirely over open ocean around Antarctica. Few scheduled flights ride it, which is partly why it gets far less attention when people talk about flight times.
The odd one out is the Tropical Easterly Jet. It forms each summer over the Indian Ocean, centred around 15°N, and blows the opposite way to every other major jet stream: east to west, not west to east. It’s driven by intense sunshine heating the Tibetan Plateau, not by the usual contrast between polar and warmer air. It’s closely tied to the Asian monsoon, forming in late June and fading by early September, the same window as the monsoon itself.
The real numbers
The world's major jet streams
50-60°
Polar jet latitude
Both hemispheres — the one most transatlantic/transpacific flights actually use
30°
Subtropical jet latitude
Both hemispheres, generally higher altitude than the polar jet
15°N
Tropical Easterly Jet
Indian Ocean, June-September — flows backwards, east to west
140+ mph
Typical core wind speed
Can exceed 275mph in an intense winter jet
How airlines actually use it
The shortest path between two airports, a great circle route, is only the starting point of a flight plan. Between San Francisco and Tokyo, the great circle runs as a fairly direct arc across the Pacific. Flying eastbound, airlines often bend well away from that line to spend longer in the jet stream’s tailwind, because the time and fuel saved by the higher ground speed outweigh the extra distance. Westbound, it works the other way: airlines steer around the strongest part of the jet where they can, since flying into it costs time and fuel. That’s the whole reason the North Atlantic Tracks exist. Rather than leave hundreds of flights to guess where the jet stream is that day, Gander and Shanwick oceanic control publish a set menu of routes twice a day, built around its measured position.
Animated
Why New York–London and London–New York fly different paths
The jet stream (the flowing band) is a river of fast wind high up, blowing west to east. Eastbound flights (green) are routed right into it for a free push and arrive early. Westbound flights (red) are routed away from it, often curving north towards Iceland and Greenland, where the headwind is weaker, even though the path looks longer. Air traffic control publishes a fresh set of these North Atlantic tracks twice a day, because the jet stream moves. Band and tracks are illustrative; map and airports are real.
Try it
Ride the jet stream: New York ⇄ London
The aircraft flies through the air at the same speed both ways (about 490 knots here). What changes is the air itself moving: with a 80-knot jet stream behind it, the eastbound flight covers the ground at 570 knots, against it only 410. That’s why the same route can differ by over an hour each way, and how a British Airways 747 topped 800 mph over the ground in a storm-driven jet stream in February 2020. Assumes the average wind along the whole route; real winds vary.
Seeing it from space
The jet stream itself is invisible, but the high cirrus clouds that often form along its edge aren’t. From orbit, that cloud can trace the jet stream across a whole coastline in one long, organised streak. In May 1991, astronauts on Space Shuttle Discovery photographed exactly that: a narrow band of jet-stream cloud crossing Cape Breton Island in eastern Canada, where winds often run from 90 to over 180mph. It’s the same feature that brought the BA 747 in early in 2020, just seen from orbit.
.jpg?width=1600)
Sources & Further Reading
Common Questions
Frequently Asked Questions
Can you actually see a jet stream?
Indirectly, yes. Jet streams themselves are invisible, but high, wispy cirrus clouds often form along their edges and trace the same narrow band. You can see that cloud from the ground, from an aircraft window, and even from orbit, where NASA astronauts have photographed it crossing whole coastlines in one long streak.
Do jet streams stay in the same place?
No. They shift all the time, in both position and strength, which is why the North Atlantic Tracks are republished twice a day instead of being fixed. The polar jet can dip much further south in winter, which is part of why winter transatlantic flight times vary more than summer ones.
Is the jet stream the same thing as regular wind?
The same physics, on a very different scale. Ordinary surface wind comes from local pressure differences near the ground. A jet stream is a concentrated ribbon of much faster wind, 4-8 miles up, driven by the temperature contrast between whole air masses: cold polar air against warmer air further from the pole. Think less “windy day” and more “the atmosphere’s main motorway”.
Why does the Tropical Easterly Jet blow the opposite direction to the others?
Because it forms for a completely different reason. The polar and subtropical jets come from the contrast between cold and warm air masses. The Tropical Easterly Jet forms over the Indian Ocean each summer because of intense sunshine heating the Tibetan Plateau. That drives the air east to west instead of the usual west to east. It’s also why it’s tied so closely to the Asian monsoon rather than to general weather further from the equator.
Last reviewed: October 2026. Facts that change, such as fleets, airspace and airline ownership, are re-checked on a schedule. Spotted an error? Email contact@skyplus.news and we’ll fix it. See how we check facts.