Cyclone Midhili

Relevance: Important Geophysical Phenomena, Disaster Management, Cyclone, Midhili, Tropical Cyclones, Anti-Cyclone, Extra Tropical Cyclones, Management of Disasters, Government Initiatives on Disaster Management

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Why in the news?

• Cyclone Midhili, moving north-northeastwards over the Bay of Bengal, is expected to intensify with winds up to 85 kmph and make landfall near the Khepupara coast of Bangladesh.

About Cyclone Midhili

• The name ‘Midhili’ for the cyclonic storm was given by the Maldives.
• Cyclone Midhili was moving north-northeastwards at 25 km/h over the northwest and adjoining northeast Bay of Bengal.
• The cyclone was centered about 30 km south-southwest of Khepupara, Bangladesh, and 250 km southwest of Chittagong, Bangladesh.
• It is forecasted to make landfall near Khepupara on the Bangladesh coast, with squally winds expected during the process.
• It is accompanied by an upper air cyclonic circulation over the southwest Bay of Bengal and adjoining Sri Lanka, and another cyclonic wind area in the south Andaman Sea.
• Heavy to very heavy rain was expected in parts of Nagaland, Manipur, Mizoram, and Tripura.
• Warnings have been issued of potential damage in coastal areas of West Bengal, particularly North 24 Parganas.

What are Cyclones?

• Cyclones are large-scale air masses that rotate around a strong center of low atmospheric pressure.
• They are characterized by inward spiraling winds that rotate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.

Favourable Conditions for Formation of Cyclones

• Warm Ocean Water: Sea surface temperatures must be around 26°C or higher. This warmth provides the necessary energy for the cyclone to form.
• Atmospheric Instability: Warm, moist air rising from the ocean surface leads to the formation of cumulus clouds, which can grow into a cyclone under the right conditions.
• Moisture in the Atmosphere: High humidity, especially in the lower and middle levels of the troposphere, aids in the development of clouds and thunderstorms within the cyclone.
• Low Wind Shear: Low levels of wind shear (changes in wind speed and direction with height) are essential. High wind shear can disrupt the cyclone's structure.
• A Pre-existing Weather Disturbance: A cyclone often forms from a pre-existing disturbance in the atmosphere, like a tropical wave, which provides an initial structure for storm development.
• Coriolis Effect: This is necessary to create the spin in the cyclone. It becomes effective at least 5° away from the equator.
• Distance from the Equator: Cyclones typically form at least 5° away from the Equator since the Coriolis effect is too weak near the Equator to create the cyclonic rotation.

Types of Cyclones

1) Tropical Cyclones

• These form over warm ocean waters near the equator.
• They are fueled by the heat from the sea and evaporated water.
• Tropical cyclones are characterized by a low-pressure center, high winds, and heavy rain.
• Depending on their location and intensity, they are known as hurricanes (Atlantic and eastern Pacific Oceans), typhoons (northwestern Pacific Ocean), and simply cyclones in the South Pacific and Indian Ocean.

Formation of Tropical Cyclones

• Formation and Early Stages
  • The initial formation and development of a cyclonic storm are driven by the transfer of heat and water vapor from the warm ocean to the air above, mainly through evaporation at the sea surface.
  • This process promotes the creation of large vertical cumulus clouds as a result of convection and the condensation of rising air over the ocean.
• Mature Stage
  • As the storm strengthens, air ascends in powerful thunderstorms and spreads horizontally at the level of the tropopause.
  • This spreading of air creates a positive pressure at higher altitudes, which in turn enhances the downward movement of air due to convection.
  • This process leads to the warming of the air by compression, forming a warm ‘Eye’ (a low-pressure center) of the storm.
  • The primary characteristic of a mature tropical cyclone in the Indian Ocean is the presence of concentric bands of turbulent, large cumulus thunderclouds.
• Weakening and Dissipation
  • A tropical cyclone starts to lose its strength, evident in the reduction of central low pressure, internal warmth, and extreme wind speeds, when its supply of warm, moist air diminishes or is suddenly cut off.
  • This typically occurs after the cyclone makes landfall or moves over cooler waters.

2) Extratropical Cyclones

• These develop in higher latitudes, generally between 30° and 60° latitude in both hemispheres.
• Unlike tropical cyclones, they form over land or water and are driven by temperature contrasts between air masses.
• Extratropical cyclones often bring widespread rain, wind, and sometimes snow.
• Frontal depressions, wave cyclones, temperate cyclones, and mid-latitude depressions are some names for extratropical cyclones.

Formation of Extratropical Cyclones

• The Polar Front theory provides the most comprehensive explanation for the formation and development of temperate cyclones.
• This theory posits that when warm and humid air from the tropics converges with the dry and cold air from the poles, a polar front is established.
• The denser and heavier cold air causes the warm air to rise.
• This interaction between the cold and warm air masses leads to instability and the creation of low pressure at their meeting point, particularly at the center of this interaction.
• This results in a pressure void, which is filled by the surrounding air.
• This incoming air, influenced by the rotation of the Earth, gives rise to a cyclone.
• In comparison, extratropical cyclones are less severe than the tropical cyclones or hurricanes, which develop in areas of more uniform temperature.

Mitigation and Preparedness Measures

• Mapping Hazards: Assessing cyclone risks and displaying them on maps.
• Regulating Land Use: Implementing policies for land use and enforcing building codes.
• Engineered Structures: Constructing buildings on stilts or earthen mounds, ensuring they are wind and water-resistant.
• Cyclone Shelters: Establishing shelters in cyclone-prone areas.
• Flood Management: Building barriers and creating water storage facilities to manage flooding.
• Plantation of Mangroves: Protecting coastal areas from storm surges.
• Public Awareness Generation: Educating the public on cyclone risks and safety measures.
• Early Warning System: Enhancing systems for rapid and efficient response.
• Community Participation: Involving local communities in developing mitigation measures

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FAQs

MCQs

Q.1) Consider the following statements: (UPSC 2020)

Jet streams occur in the Northern Hemisphere only.

Only some cyclones develop an eye.

The temperature inside the eye of a cyclone is nearly 10°C lesser than that of the surroundings.

Which of the statements given above is/are correct?

(a) 1 only

(b) 2 and 3 only

(c) 2 only

(d) 1 and 3 only

Q.2) In the South Atlantic and South-Eastern Pacific regions in tropical latitudes, cyclone does not originate. What is the reason? (UPSC 2015)

(a) Sea surface temperatures are low

(b) Inter-Tropical Convergence Zone seldom occurs

(c) Coriolis force is too weak

(d) Absence of land in those regions