The narrow bands of strong winds flowing in west to east direction in the upper layers of atmosphere are termed as jet streams. These strong currents of air circulating the earth are formed where air masses of differing temperature meet. Jet streams usually have a meandering snake-like waves. Our earth has two polar jet streams, one at each pole, and two sub-tropical jet streams near the equator.
What Causes Jet Streams?
When warm air from earth meets the cooler air mass in the atmosphere, the warm air tends to move up and cooler air rushes to fill the void created by the rising warm air. This movement creates a strong air current. Formation of strong air currents on the meeting boundary of warm and cold air usually happen near the tropopause (area between troposphere and stratosphere) at a height of about 5 to 9 miles. Warmer tropical air blows towards the cooler northern air and gets deflected towards east due to the movement of earth. This is the reason jet stream flow from west to east.
Since the temperature difference between warm air and cold air is starker during winters, the jet streams are strongest during the winter. The winds in jet streams blows at a speed ranging between 129 to 225 kilometers per hour. But, can also reach up to 443 kilometers per hour.
How Jet Streams Affect the Weather?
Jet Streams are not a stationery phenomenon. They keep moving to higher or lower altitudes, shifting in flow, breaking or changing speed all depending on season and other variables like amount of solar radiation. For example, jet streams tend to move towards equator during winters and move back to poles during the spring. This shifting pattern of jet streams can have a significant impact on weather.
Jet streams affects the onset and withdrawal of monsoon winds significantly. It intensifies the alternative cyclonic and anti-cyclonic conditions. Jet stream is also known to have brought some ozone depleting substances to stratosphere. It is also associated to alternating high pressure and low pressure as the moving air undergoes alternate expansion and compression. In fact, weather satellites are used by meteorologists to detect and monitor jet stream for forecasting weather conditions.