Monsoons and jet streams | Climatology | Principle Of Geography

 

Climatology

Principle Of Geography

Geography Complete Study Material

(Paper - I)

Monsoons and Jet Streams

            There are different jet streams and in respect of the climate and monsoons of India, it is the Subtropical Jet Stream (STJ) and the countering easterly jet that is most important. As the summertime approaches there is increased solar heating of the Indian subcontinent, this has a tendency to form a cyclonic monsoon cell situated between the Indian Ocean and southern Asia. This cell is blocked by the STJ which tends to blow to the south of the Himalayas, as long as the STJ is in this position the development monsoons is inhibited. During the summer months, the STJ deflects northwards and crosses over the Himalayan Range. The altitude of the mountains initially disrupts the jet but once it has cleared the summits it is able to reform over central Asia. With the STJ out of the way, the subcontinental monsoon cell develops very quickly indeed, often in a matter of a few days. Warmth and moisture are fed into the cell by a lower level tropical jet stream which brings with it air masses laden with moisture from the Indian ocean. As these air masses are forced upward by north India’s mountainous terrain the air is cooled and compressed, it easily reaches its saturation vapor point and the excess moisture is dissipated out in the form of monsoon rains. The end of the monsoon season is brought about when the atmosphere over the Tibetan Plateau begins to cool, this enables the STJ to transition back across the Himalayas. This leads to the formation of a cyclonic winter monsoon cell typified by sinking air masses over India and relatively moisture-free winds that blow seaward. This gives rise to relatively settled and dry weather over India during the winter months.

             Jet streams are high-speed winds that occur in narrow bands of upper air westerlies. The width of this airband can be 160-480km wide and 900-2150m thick, with core speed exceeding 300km/hr. such is their strength that aircraft routes which run counter to jet movements are generally avoided. Jets are coincident with major breaks in the tropopause.

Genesis of Jet Streams 

The genesis of the Jet-streams is provided by three kinds of gradients: 

• The thermal gradient between pole and equator 
• The pressure gradient between pole and equator 
• The pressure gradient between surface and subsurface air over the poles.

Types of jet Streams 

• Polar front jet streams 
• Subtropical Westerly Jet streams 
• Tropical easterly Jet streams 
• Polar night Jet Streams 
• Local Jet Streams

             Jets streams play a key role in determining the weather because they usually separate colder air and warmer air. Jet streams generally push air masses around, moving weather systems to new areas and even causing them to stall if they have moved too far away. Climatologists say that changes in the jet streams are closely tied to global warming, especially the polar jet streams because there is a great deal of evidence that the North and South poles are warming faster than the remainder of the planet. When the jets streams are warmer, their ups and downs become more extreme, bringing different types of weather to areas that are not accustomed to climate variations. If the jet stream dips south, for example, it takes the colder air masses with it.