What are jet streams ?
Jet streams are basically narrow bands of strong winds. They exist at around 12 km above the surface of the Earth, in the upper levels of the atmosphere. They specifically lie in the middle and upper troposphere or lower stratosphere. These are the meandering air currents, which typically flow northeastward, eastward, and in southeastward directions.
What causes jet streams?
The jet streams in the atmosphere are a result of the meridional (that is, equator-to-pole) temperature gradient in the earth's atmosphere. This thermal gradient cause large scale air circulation cells. These cells are then acted upon by the Coriolis force generated due to planet's rotation.
The temperature gradient arises from the differential solar heating of the spherical surface of a planet. The surface is generally warmest at the equator and grows progressively cooler as one moves pole-ward. When two air masses of different densities meet, the pressure created by the different densities cause winds to increase. As these winds attempt to flow from the warm area in the nearby stratosphere down into the cooler troposphere, they are deflected by the Coriolis force and eventually start flowing along the boundaries of the original two air masses.
The velocity of the jet stream is proportional to the intensity of this thermal gradient. During the winter months, the equator-to-pole temperature disparity is at its greatest. Thus, the jet stream reaches its maximum velocity during winter. On the contrary, During the summer months, the temperature gradient between the equator and the pole is considerably less (only about half the winter value). As a result, the jet stream reaches its minimum velocity during summers.
Types of Jet Streams -
There are basically two main types of jet streams, "The Polar Jets" and "The Subtropical Jets". The Polar jets exist at 9-12 km above sea level whereas the subtropical jets exist at 10–16 km above the sea level. It has been noticed that the Subtropical ones are somewhat weaker than the Polar ones.
How do they influence us?
The jet streams flow high overhead and cause changes in the wind and pressure at that level. They follow the boundaries between hot and cold air and affect things nearer the surface. These things include the areas of high and low pressure, eventually shaping the weather conditions we see.
Moreover, Jet streams can influence flights to a great extent and it was first discovered during Word War II. When the American bombers tried flying from the U.S. to Japan, they found that they couldn't make any progress flying against the strong winds. However, moving in the direction of jet streams give rise to completely opposite consequences. For example, recently, an insanely powerful Jet Stream boosted an Airplane to a speed of over 800 Mph, which is about the speed of sound. And, thanks to this jet stream buffer, the flight landed at London Heathrow 48 minutes earlier than the scheduled time.
Interesting ! Aren't they?