Question – How, as a result of changes in upper atmospheric circulation, extratropical cyclones are formed? Explain the difference between tropical and extratropical cyclones. – 23 March 2022
Answer – An extratropical cyclone is a low pressure air system, which derives its energy mainly from the horizontal temperature present in the atmosphere. It is a low pressure cyclone originating between the middle and high latitudes. This type of cyclone is also called Lehar cyclone or mid latitude cyclone.
Upper atmospheric circulation and formation of extratropical cyclones
In the classical model, a cyclone originates as a low-pressure disturbance on an existing stationary front. Fronts are atmospheric discontinuities in temperature, moisture, and wind shear. The frontal boundary deforms as cyclonic circulation develops, with active fronts leading the cold air north and west of the low and the warm air equatorward of the low in a cyclonic migration about the center of the low.
An extratropical cyclone is a low pressure air system, which derives its energy mainly from the horizontal temperature present in the atmosphere. It is a low pressure cyclone originating between the middle and high latitudes. This type of cyclone is also called mid latitude cyclone.
Fig: Upper air and surface circulation of extratropical cyclone
There are pockets of warm air or warm sectors wedged between the forward and the rear cold air or cold sector. The warm air glides over the cold air and a sequence of clouds appear over the sky ahead of the warm front and cause precipitation. The cold front approaches the warm air from behind and pushes the warm air up. As a result, cumulus clouds develop along the cold front. The cold front moves faster than the warm front ultimately overtaking the warm front. The warm air is completely lifted up and the front is occluded and the cyclone dissipates.
There are pockets of warm air or warm sectors, wedged between the forward and the rear cold air or cold sector. The warm air glides over the cold air and a sequence of clouds appear over the sky ahead of the warm front and cause precipitation. The cold front approaches the warm air from behind and pushes the warm air up. As a result, cumulus clouds develop along the cold front. The cold front moves faster than the warm front ultimately overtaking the warm front. The warm air is completely lifted up and the front is occluded and the cyclone dissipates.
Fig: Occluded Front
Difference between Tropical and Extratropical cyclones:
| Base | Tropical cyclone | Extratropical cyclones |
| Typical Properties
|
It is formed between the lines of Cancer and Capricorn. Its main thing is that they are very active in the middle of the oceans, but they become weak by reaching the land. Therefore, they are able to remain more effective only on the coastal parts of the continents. These cyclones mainly originate over the oceans in both the hemispheres between 5° to 15° latitudes. | Cyclones that originated in tropical regions (between 30° and 60° latitude from the equator) through cyclogenesis or extratropical transition are called biotropical cyclones. Their height in the atmosphere ranges from 10 to 12 km and length from 160 km to 3200 km. Their average speed is 32 kilometers per hour in summer and 48 kilometers per hour in winter. |
| Configuration
|
The combination of warm ocean temperatures, high relative humidity and atmospheric instability is the main cause of tropical cyclones. | This cyclone is generated by the combination of winds coming from the polar regions with the winds coming from the tropical regions. |
| Direction
|
It runs from east to west. | It runs from west to east. |
| nature of cyclone
|
Strong storm | Steady storm |
| type | Hot Air System | Cold Air System |
