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VisionIAS - Video Classroom Lecture
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Geography Class 02

JET STREAMS: (1:15:27 PM):

  • Strong narrow currents concentrated along a quasi-horizontal axis/ semi-horizontal axis in the upper troposphere or in the lower stratosphere characterized by strong vertical and lateral wind Shear featuring one or more velocity maxima
  • It meanders in both axes, i.e. horizontally as well as vertically
  • Characteristics of the Jet stream 
  • They are 1000s of KM in length and 100s of KM in width
  • It normally moves from west to east
  • It follows a Zig-Zag path in the form of Rossby waves
  • Winds are faster during winter
  • The entire system follows the sun changing its position with the season
  • Formation of Jet streams:
  • It is due to the temperature difference between the two regions on the surface the jet streams are generated, for example, tropical and temperate regions
  • The difference in temperature results in a difference in pressure gradient with altitude above warm and cold air masses causing the generation of strong winds. 
  • They become geostrophic in nature. 
  • The larger the temperature difference, the stronger will be the winds. 
  • Types of the Jet stream (1:56:52 PM):
  • Polar front jet stream-
  • Formed where Ferrel and polar cells interact
  • Irregular and discontinuous
  • Direction- West to east
  • Subtropical westerly Jet stream 
  • Associated with temperature gradient between Hadley cell and Ferrel cell
  • Direction- West to east
  • It is more consistent and strong
  • Tropical easterly jet stream
  • Forms over Indian and Africa in the summer
  • It is due to the intense heating of the Northern Plains and Tibetan plateau
  • Direction- East to west
  • Local jet streams 
  • Formed due to local differences in temperature and pressure conditions
  • Example- Somali jet stream
  • Polar night jet stream 
  • They formed over polar regions during winters
  • Direction- West to east
  • Significance of jet stream:
  • The jet streams are responsible for Cyclonic and Anticyclonic circulations along the surface. Upper divergence in Jet stream causes lower convergence and upper convergence causes lower divergence 
  • It changes the weather conditions by suppressing or supporting precipitation
  • They are still used in aircraft navigation
  • The polar night jet streams are responsible for ozone depletion in polar regions during winters resulting in the formation of Ozone holes.
  • During winters, the bad air quality due to calm winds and radiation inversion is disturbed by the jet streams.
  • It helps in the transportation of pollutants into the upper troposphere from urban regions 
  • The jet streams are helpful in the formation of temperate cyclones. 
  • The Monsoon in South Asia is affected by the subtropical westerly jet stream, Tropical easterly Jetstream, and Somali jet stream  [* Indian physical geography]
  • The subtropical westerly jet stream is responsible for winter rainfall along North-western India through Western disturbance [* Indian physical geography]
  • Jet streams along with La Nina conditions can result in the trapping of the hot air causing heat dome over the land [* Oceanography]
  • The weakening of jet streams disturbs the atmospheric conditions and during the winters it may cause the outbreak of the polar vortex

POLAR VORTEX: (2:42:21 PM):

  • It is a large area of low pressure and cold air surrounding the earth's poles. 
  • The term vortex refers to the counter-clockwise flow of air which keeps the cold polar air locked inside
  • The polar winter night jet streams keep this region covered with strong winds. Occasionally, when the vortex weakens due to the weakening of Jet streams, the vortex expands and sends cold air southwards along with jet streams. This brings down the temperature in southern regions to colder levels of below zero degrees Celsius

AIR MASS: (3:10:12 PM):

  • It is an extensive portion of the atmosphere whose physical properties such as temperature, pressure, and humidity are uniform horizontally and vertically over 100s of KM 
  • Characteristics:
  • The temperature of the source area shall remain uniform horizontally with a very gradual change in the vertical direction 
  • The humidity conditions should also be uniform with the least variability. The surface area shall remain homogenous for a few 100s of KM. 
  • Ex- Oceans and deserts.
  • Regions with Light divergent winds, High-pressure belts, and anti-cyclonic conditions are more favorable for the formation of Air masses due to stable conditions

Types of air masses: 

  •                                                  Air Mass

    Source area

    o   Continental

    o   Maritime

    Temperature

    o   Warm 

    o   Cold

    Pressure

    o   Stable 

    o   Unstable

    Latitude

    o   Arctic (A)

    o   Antarctic (AA)

    o   Polar (P)

    o   Tropical (T) 

    o   Equatorial (E)
  • Significance of Air masses:
  • Air masses transport heat from 1 region to another and help in the global distribution of temperature.
  • Air masses moving from 1 region to another change the atmospheric conditions of destination regions.
  • Maritme air masses bring more moisture towards continental regions increasing their humidity and causing precipitation along the coasts.
  • Maritme air masses of the Indian Ocean bring good precipitation over India.
  • The dry continental air mass that develops over subtropical regions helps in maintaining arid conditions for a longer duration.
  • The cold air mass formed over Siberia and Canada affects the surrounding regions for long distances and causes freezing conditions.
  • The maritime tropical and equatorial air masses in the Indian and Atlantic oceans favor the development of tropical cyclones.
  • The merging of warm and cold air masses leads to the formation of fronts, frontal inversion, frontal rainfall, and temperate cyclones.

The topic for the next class-Fronts.