What is the Jet stream?

JET STREAM

In the troposphere, the north south temperature gradient increases with altitude. This causes a general increase in pressure gradient that give rise to strong wind in the upper troposphere. This high speed wind formed in narrow belt in the upper troposphere is termed as Jet stream. These winds are normally westerly wind. The average wind speed of the Jet stream is about 144km/hr. But its velocity at inner core reaches magnitude as high as 480km/hr. The existence of Jet stream was discovered during the Second World War, the high speed wind in the upper troposphere drastically altered the speed of the Americans bombers. The vertical temperature gradient is very large compared to the horizontal temperature gradient. Besides the latitudinal temperature gradient causes pressure gradient to increase with height.

This is the main reason for the existence of Jet stream. It exists at an elevation of 9000 to 12000m in the mille latitudes and at a smaller height in higher latitude. They exhibit a significant seasonal variation. In winter, they move toward equator and in summer they move towards the pole. In the process, the velocity is altered. The velocity is higher in winter than in summer. This is mainly smaller pressure gradient in summer. The Jet stream is almost parallel to the latitude. However, their paths have been observed to meander in the North South direction. As a result, they have southern and northern component as well. These Jet streams tend to change the path and the annual cycle of the Jet follow a general pattern refer to as index cycle.

They flow from west to east, so are mostly westerly in nature however easterly Jet winds have been observed in the South-East Asian monsoon during the summer. The study of upper air Jet stream is becoming more significant as it is believed to associate with surface weather. The path followed by the cyclones and their consequent whether distribution, is believed to be significantly altered by the position and strength of the Jet stream as more upper air data becomes available. The nature of the Jet stream and its impact on the weather can be more accurately predicted till now, no relationship is discovered but evidence suggest its association with surface weather.