Question.
The formation of a temperate cyclone depends on the conditions of the axis of dilation. Elucidate.
( UPSC Geography: Climatology; NCERT: Class: XI-Chapter:9)
Answer:
Temperate cyclones (also called mid-latitude cyclones or extratropical cyclones) are large-scale low-pressure systems that develop in the mid-latitudes between 30° and 60° N and S.
The formation of these cyclones is largely governed by the upper atmospheric conditions, particularly the axis of dilation.
What is the Axis of Dilation?
It refers to a zone in the upper troposphere ( approx. 10 to 12 km above the Earth's surface) where air masses diverge or spread out.
This divergence creates a suction effect at the surface, promoting the uplift of air and the intensification of surface low pressure.
Role of Axis of Dilation in Temperate Cyclone Formation:
Presence of Warm and Cold Air Masses:
Two air masses of different temperature and density meet at the Axis of Dilation, such as cold polar air and warm subtropical air.
These currents form a cold front and a warm front, where there is a sharp change in air pressure.
Upper Tropospheric Divergence:
The axis of dilation occurs at the jet stream level.
Divergence aloft causes air to rise from the surface, initiating cyclogenesis.
It deepens the surface low and strengthens the cyclone.
Atmospheric disturbance:
When this situation becomes unbalanced, atmospheric disruption occurs, which seeds the cyclone.
Effect of Coriolis force:
The Coriolis force caused by the rotation of the Earth forces these winds to rotate, thereby forming a cyclonic circulation.
Jet stream Support:
If the position of the jet stream is above the dispersion axis, it provides divergence from above and helps in intensifying the cyclone.
Example:
Many temperate cyclones in the North Atlantic region between America and Europe originate on the Axis of Dilation.
Western Disturbances in North India are also based on this principle.
The Axis of Dilation is the main geographical position where temperate cyclones originate. This axis is the line of imbalance of wind, temperature, and air pressure, which becomes the source of energy of the cyclone. Hence, its location and position play a very important role in the formation of a temperate cyclone.
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