The fronts occur in middle latitudes and are characterised by steep gradient in temperature and pressure. They bring abrupt changes in temperature and cause the air to rise to form clouds and cause precipitation.
The Extra-Tropical Cyclones are storm systems emerging in the mid and high latitudes, away from the tropics.
- They are low-pressure systems with associated cold fronts, warm fronts, and occluded fronts.
- These cyclones are formed along the polar front.
- These cyclones move from west to east but tropical cyclones, move from east to west.
- In the beginning, the front is stationary.
- Extra-tropical cyclones are also known as mid-latitude storms or baroclinic storms.
- In the Northern hemisphere, cold air blows from the north of the front and warm air blows from the south.
- When the pressure descents along the front, the cold air move towards the south and the warm air moves northwards setting in motion an anticlockwise cyclonic circulation.
- The cyclonic circulation results in a well-built extratropical cyclone, with a cold front and a warm front.
- The warm air climbs over the cold air and a series of clouds appear over the sky ahead of the warm front and cause rainfall.
- The cold front approaches the warm air from behind and pushes the warm air up.
- As an outcome, cumulus clouds develop along the cold front.
- The cold front moves faster than the warm front eventually surpassing the warm front.
- The warm air is entirely lifted up and the front is occluded and the cyclone dissipates.
- They can originate over the land and sea and cover a larger area.
- This cyclone affects a much larger area as compared to the tropical cyclone.
- The velocity of wind in a tropical cyclone is much higher and it is more damaging.
- Tropical cyclones are regarded as one of the most devastating natural calamities in the world.
- They originate and intensify over warm tropical oceans.
- These are ferocious storms that originate over oceans in tropical areas and move over to the coastal areas causing violent winds, very heavy rainfall, and storm outpourings.
NAMES OF CYCLONE IN DIFFERENT REGIONS
- They are known as:
- Cyclones in the Indian Ocean
- Hurricanes in the Atlantic
- Typhoons in the Western Pacific and the South China Sea
- Willy-willies in Western Australia
CONDITIONS FOR THE FORMATION OF TROPICAL CYCLONE
- The conditions which favour the formation and intensification of tropical cyclone storms are:
- Large sea surface with a temperature higher than 27° C
- Presence of the Coriolis force
- Small differences in the vertical wind speed
- A pre-existing weak- low-pressure area or low-level-cyclonic circulation
- Upper divergence above the sea level system
Formation of Cyclone
- The energy that strengthens the storm comes from the condensation process in the towering cumulonimbus clouds, surrounding the centre of the storm.
- With an uninterrupted supply of moisture from the sea, the storm is again strengthened.
- On reaching the terrestrial region the moisture supply is cut off and the storm dissipates.
- The place where a tropical cyclone cuts the coast is called the landfall of the cyclone.
- A landfall is frequently accompanied by sturdy winds, heavy rain and mounting sea waves that could threaten people and cause damage to properties.
- Cyclones which cross 20 degrees North latitude are more destructive.
- They cover a larger area and can originate over the land and sea whereas the tropical cyclones originate only over the seas and on reaching the land they dissipate.
EYE OF CYCLONE
- A mature tropical cyclone is characterised by the strong spirally circulating wind around the centre which is called the eye.
- The eye is an area with calm weather descending air.
- It is characterized by light winds and clear skies.
- Around the eye is the eyewall, where there is a strong spiralling rise of air to a greater height reaching the tropopause.
- The wind reaches maximum velocity in this region and torrential rain occurs here.
- From the eyewall, rain bands may radiate and trains of cumulus and cumulonimbus clouds may drift into the outer region
DIFFERENCE BETWEEB CYCLONE AND ANTI CYCLONE
The extra tropical cyclones have a clear frontal system
which is not present in the tropical cyclones.
They cover a larger area and can originate over the land and sea.
Whereas the tropical cyclones originate only over the seas and on reaching the land they dissipate.
The extra tropical cyclone affects a much larger area as compared to the tropical cyclone.
The wind velocity in a tropical cyclone is much higher and it is more destructive.
The extra tropical cyclones move from west to east but tropical cyclones, move from east to west.
Thunderstorms are storms ranging several kilometres in diameter, created by the rapid lifting of moist and warm air, as a result of which a dense vertical tower of the cloud is created. Thunderstorms are associated with strong winds, hail, lightning, tornadoes, thunder and heavy rain.