GEOGRAPHY-CLASS-9-18/09/2021

 

STAGES OF A WAVE CYCLONE:

TEMPERATE CYCLONE:

STAGES OF TEMPERATE CYCLONE:

1.INITIAL STAGE:

In the initial stage, the air masses flow parallel to each other which creates stationary fronts.

2.FRONTOGENESIS:

Genesis means “formation”.

Due to disruption in the stationary front, the warm air mass enters into the region of cold air mass and vice versa. It creates cyclonic circulation around the low-pressure system formed between the center of two fronts. Cyclonic pattern rotates in an anticlockwise direction in the northern hemisphere and clockwise in the southern hemisphere.

3.MATURE STAGE:

Here both cold and warm fronts advance each other. Since the cold font is heavier than the warm front, it tries to catch up with the warm front.

4.FRONTOLYSIS:

Here both cold and warm front merges and forms an occluded front. After this occlusion stage, cold air mass completely uplift the warm air mass which results in the dissipation or death of temperate cyclones.

DIFFERENCE BETWEEN CHARACTERISTICS OF TEMPERATE AND TROPICAL CYCLONE:

TEMPERATE CYCLONE

TROPICAL CYCLONE

Presence of frontal system.                                              It follows the path of westerlies.(latitude-23 ½ deg N-66 ½ deg S.) It’s horizontal diameter is about            160-3200 km and extends for about 10-12km vertically. Can be formed in both land & water. Temperate cyclones will be in inverted ‘V’ shape or circular. Wind velocity is lesser. In India it is known as western disturbance-extra tropical cyclone from the Mediterranean Sea.

Absence of frontal system. It follows the path of trade winds(easterlies). It’s diameter is about 160-300 km(approximately). Formed only in water. Tropical cyclones will be in elliptical shape. Wind velocity is high - 221 km/hr and hence it is called a super cyclone. It occurs along the west and east coast of India.

TROPICAL CYCLONE:

CONDITIONS FOR FORMATION OF TROPICAL CYCLONES:

• Large sea surface with temperature above 27 deg Celsius.
• Presence of Coriolis force.
• A pre-existing weak low-pressure region.
• Small variation in the vertical wind speed.
• Upper divergence above the sea level.

FORMATION:

In a pre-existing low-pressure system, the wind starts to converge and rises towards the upper troposphere where it condenses and forms clouds. Here the water vapour is changed into clouds with the release of extra latent heat which intensifies the existing low pressure, resulting in the more amount of wind convergence. This forms a calm region called the eye in the low-pressure region and funnel shaped eye wall.

Wind starts to spiral inwards around the eye wall region. The tropical cyclones follow the path of tropical easterlies or trade winds which pushes the entire cyclonic system towards land.

When an eye of the cyclone crosses the land, the moisture supply will be cut off. Then the cyclone will be dissipated(dead).

Tropical cyclones are marked with cumulonimbus clouds and size varies from 150-300km.

CURRENT AFFAIRS :

Due to increase in global warming, the intensity and frequency of tropical cyclones increases in Arabian sea which results in high rainfall and frequent cyclones and temperate cyclones move slowly due to global warming.

VARIOUS NAMES OF TROPICAL CYCLONES:

• Indian ocean – Tropical cyclone
• Philippines – Baggeus
• East China – Typhoons
• North Atlantic region - Hurricanes
• Australia – Willy willies

CATEGORIES OF CYCLONE	SUSTAINED WINDS (3-min average)
Super cyclonic storm	>= 221 km/hrs.
Extremely severe cyclonic storm	166-220 km/hrs.
Very severe cyclonic storm	118-165 km/hrs.
Severe cyclonic storm	89-117 km/hrs.
Cyclonic storm	63-88 km/hrs.
Deep depression	51-62 km/hrs.
Depression	31-50 km/hrs.

Jet streams will be continued in the next class.

Credits:Leo Rajalakshmi