Tracking the jet streams from space
Jet streams are fast-moving currents of air that are the drivers of the weather we experience at the Earth’s surface. These narrow air currents are found high in the atmosphere, near the tropopause, which is a boundary between the troposphere – where most weather happens and air gets cooler with height – and the warmer layer of the stratosphere, where ozone absorbs energy from the sun.
The streams are driven by the temperature contrast between the poles and the equator, caused by the uneven heating of the Earth’s surface. The greater the contrast in temperature, the faster the wind speed in the jet. This image shows the air masses and jet streams in the Southern Hemisphere – the pattern of airmasses and jet streams from the equator towards the poles is similar in both hemispheres, but because there is less land in the Southern Hemisphere, the jet streams can be stronger there.
There are two types of jet stream — polar and sub-tropical. Polar jet streams are the more powerful of the two and are typically located seven to 12 km above sea level. The weaker sub-tropical jet streams are usually situated 10–16 km above sea level.
The width of a jet stream is typically a few hundred kilometres and each one is only a few kilometres deep. But they extend for thousands of kilometres around the planet. They are usually continuous, but meandering, over these long distances. They normally take a general west to east path across the Atlantic – although with different ripples and bulges.
The jet steers the areas of low and high pressure in the atmosphere that cause different sorts of weather on the ground. The curve in the jet can help develop or destroy areas of low pressure, leading to the decay of storms. This helps forecasters and computer models to predict storms.
In Europe, the jet stream often moves north during the summer, deflecting low pressure systems that have come across the Atlantic, and allowing for more settled conditions. In winter, the jet stream can be expected to move further south, allowing storms from the Atlantic to reach Europe hitting Ireland, the United Kingdom, and France first.
In winter 2014 the North Atlantic jet stream was 30% stronger than normal and as a result many parts of Europe were battered by a number of extremely severe storms. At this time, the jet stream was reaching Europe around the area of the Bay of Biscay – there are more details in the case study.
This Airmass RGB animation shows the sequence of storms between 29 January 2014 and 11 February 2014.
On the Airmass RGB animation the jet stream is seen initially in the top left-hand corner of the frame, constantly ‘pushing’ swirling clouds towards the western edges of Europe. Here’s part of the same sequence of storms (from 29 January 00:00 UTC–09 February 23:45 UTC) seen from another angle:
On the image below you can see the position of the jet stream, where there is a colour difference – red changes to purple.
In water vapour images the location of the jet stream can be identified as a strong gradient from high to low humidity (from white to dark colours) on side of the frontal cloud bands that is facing towards the pole.
For aviation the jet stream makes for a faster journey from west to east over the Atlantic, but is also a source of turbulence.