Jet Stream
Jet streams are fast-flowing, narrow bands of wind in the upper atmosphere (typically 9–16 km altitude), reaching speeds of 160–480 km/h, found near the boundaries between cold polar air and warmer subtropical air. They flow generally west to east and meander in wavy paths, significantly influencing surface weather by steering storm systems, affecting flight times, and modulating temperature patterns. There are two main jet streams in each hemisphere: the polar jet and the subtropical jet.
Comparison of Polar and Subtropical Jet Streams
| Feature | Polar Jet Stream | Subtropical Jet Stream |
|---|---|---|
| Latitude | 50–60°N/S | 20–30°N/S |
| Altitude (km) | 9–12 | 12–16 |
| Wind Speed (km/h) | 160–480 | 120–200 |
| Seasonal Variation | Strong in winter | More consistent |
| Weather Influence | Steers mid-lat storms | Guides tropical moisture |
| India Relevance | Affects north India winter | Controls monsoon onset |
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Related Terms
Coriolis Effect
The Coriolis Effect is the apparent deflection of moving objects — including air and water — caused by Earth's rotation. In the Northern Hemisphere, objects are deflected to the right of their direction of motion; in the Southern Hemisphere, they are deflected to the left. This effect is responsible for the rotation of large-scale weather systems such as cyclones and anticyclones, as well as global wind patterns like the trade winds and westerlies.
Wind
Wind is the horizontal movement of air from regions of high atmospheric pressure to regions of low atmospheric pressure, caused by differential heating of the Earth's surface. The speed and direction of wind are determined by the pressure gradient force, the Coriolis effect (due to Earth's rotation), and friction with the surface. Wind is a major driver of weather patterns, ocean currents, and climate, and is harnessed as a renewable energy source through wind turbines.
Atmospheric Pressure
Atmospheric pressure is the force per unit area exerted by the weight of the overlying column of air in the atmosphere on any surface below it. At sea level, the standard atmospheric pressure is 101,325 Pa (or 1013.25 hPa / 1 atm), and it decreases with altitude as the mass of air above decreases. Atmospheric pressure differences drive wind and weather systems: low-pressure zones are associated with storms and clouds, while high-pressure zones bring clear, calm conditions.
The term "jet stream" was coined by Chicago meteorologist Carl-Gustaf Rossby in the 1940s, though pilots during World War II first observed extreme high-altitude winds during strategic bombing missions. "Jet" refers to the narrow, high-speed flow resembling a jet of water.