Temperate Cyclones

• Cyclones are local low-pressure systems, with converging air from the surrounding areas.
• The Coriolis force causes the whirling motion in cyclones.
• Cyclones in the Northern Hemisphere move counter-clockwise, and clockwise in the Southern Hemisphere.

Sub-categorization of Cyclones

• Temperate Cyclones
• Tropical Cyclones

Temperate Cyclones

• Affect weather in middle latitude regions.
• They are also called extra-tropical, mid-latitude, or frontal cyclones.
• Low pressure systems with cold, warm, and occluded fronts.

Features of Temperate Cyclones

• They originate between 35-65 degrees North and South, more pronounced in the Northern Hemisphere.
• They emerge from front formation involving two contrasting air masses.
• Shapes vary from circular to elongated.
• Size ranges from 300-2000 km in diameter.
• They usually travel from west to east.
• In the Northern Hemisphere, they rotate counter-clockwise around a low-pressure center and clockwise in the Southern Hemisphere.
• They most frequently occur between September and May.

Formation of Temperate Cyclones

• Stage 1 (Frontogenesis): Two air masses meet along the sub-polar low-pressure zone, forming a border with winds blowing parallel but in opposite directions.
• Stage II (Cyclogenesis): Gradual invasion of air masses, leading to wave production and cyclonic circulation.
• Stage III (Mature Stage): Circulation sets in, air masses intrude into each other's territory.
• Stage IV (Occlusion Stage): The cold front intrudes into the warmer front, causing shrinkage/overtake, air masses combine, and the cyclone dies.

Distribution of Temperate Cyclones

• They extend over the Sierra Nevada, Colorado region, Great Lakes region, Mediterranean, Russia, and India (Western disturbances).

Weather Conditions of Temperate Cyclones

• Result in thunderstorms and heavy showers that bring wind gusts, torrential rain, and sometimes hail.
• Tornadoes can be caused by temperate cyclones which can damage buildings, trees, and electricity lines.
• Large waves at coastlines can be produced and can result in flooding and beach deterioration.
• Other prevalent weather conditions associated include strong winds, rain or snow, and thunderstorms.

Tropical Cyclones

• They are organized circulations, warm-core low-pressure systems over tropical or subtropical waters, lacking fronts.
• Hurricanes (America), Willy-willies (Australia), Typhoons (China), and Cyclones (India) are different names.

Features of Tropical Cyclones

• Confined between the tropics and smaller than temperate cyclones.
• Cyclonic wind movements are counter-clockwise in the Northern and clockwise in the Southern Hemisphere due to the Coriolis Effect.
• Diameter ranges from 30km to 300km.
• Velocity ranges from 32km/hr to over 180km/hr.
• They travel from East to West due to trade winds.
• Nature is Tropical Cyclones.

Requirements for Tropical Cyclogenesis

• Warm sea surface temperatures
• Atmospheric instability
• High humidity in the lower to middle troposphere
• Coriolis force for a low-pressure center
• Existing low-level focus or disturbance
• Low vertical wind shear

Structure of Tropical Cyclones

• Eye: Calm region at the center, usually circular, 40-65 km in diameter.
• Eye Wall: Surrounds the eye with the most severe weather.
• Rain Bands: Aligned with horizontal winds spiraling from the eyewall.

Stages of Formation of Tropical Cyclones

• Formation and Initial Development Stage: Evaporation and massive vertical cumulus clouds emerge.
• Stage of Maturity: Air rises and spreads, resulting in a heated eye (low-pressure center).
• Mature Stage: Low pressure, interior warmth, and high speeds decrease upon hitting land or cold water.

Naming of Cyclones

• Each Tropical Cyclone basin has rotating lists of names.
• WMO/ESCAP: A naming system was agreed upon in 2004 by 8 member countries for the Bay of Bengal and Arabian Sea.
• Current countries include: Bangladesh, India, Maldives, Myanmar, Oman, Pakistan, Sri Lanka and Thailand, and 5 new ones.
• The World Meteorological Department (WMO) adopted a new list comprising 13 names for each of the 13-member countries in April 2019.

Significance of naming

• Reduces confusion when two cyclones occur.
• Helps scientific identification and preventive measures.
• Assists in information dissemination worldwide.

Difference between Bomb Cyclone and Hurricanes

• Bomb Cyclone: Cold air and fronts are essential, form from late fall to early spring, originate over the northwestern Atlantic/Pacific/Mediterranean, and occur where warm and cold air meet.
• Hurricanes: Cold air rapidly weakens them, form from late spring to early fall, originate in tropical waters, and rely on warm ocean waters.

Factors affecting cyclones

• Tropical Cyclones form at tropical areas whereas Extra-Tropical Cyclones form at Mid latitudes.
• Tropical Cyclones derive energy from the latent heat of condensation but Extra-Tropical Cyclones derive energy from horizontal contrast in temperatures.
• Tropical Cyclones move from East to West however Extra-Tropical Cyclones move from West to East.
• Tropical Cyclones can only originate in deep warm oceans but Extra-Tropical Cyclones can originate over oceans as well as land.
• Tropical Cyclones have warm core shape however Extra-Tropical Cyclones have cold core shape.
• Tropical Cyclones have convectional formation but Extra-Tropical Cyclones have frontal formation.
• Tropical Cyclones diameter ranges from 50-300 km but Extra-Tropical Cyclones diameter ranges from 150-3,000 km.
• Tropical Cyclones have No temperature variation in different parts. but Extra-Tropical Cyclones Have considerable temperature variation because of different fronts

Cyclone Risks in India

• Category I (Higher vulnerability): Andhra Pradesh, Gujarat, Odisha, Tamil Nadu, and West Bengal
• Category II (Lower vulnerability): Maharashtra, Karnataka, Kerala, Goa, Pondicherry, Lakshadweep, Daman and Diu, Andaman and Nicobar Islands

India's cyclone classifcation

• Low Pressure area: Less than 31 kmph
• Depression: 31 to 49 kmph
• Deep Depression: 50 to 61 kmph
• Cyclonic Storm: 62 to 88 kmph
• Severe Cyclonic Storm: 89 to 118 kmph
• Very Severe Cyclonic Storm: 119 to 221 kmph
• Super Cyclone: More than 221 kmph

Reasons for High Cyclonic Activity in Arabian Sea

• Global warming has increased sea surface temperatures by 1.2-1.4 degrees C.
• allows Arabian Sea to provide adequate energy for storm intensification.
• provides favorable wind shear.
• Increasing El Nino Modoki causes unsuitable conditions in the Bay of Bengal and favorable conditions in the Arabian Sea.
• Warming of west wind drift is pushing warm waters into the Arabian Sea, developing a positive feedback system.

NDMA Guidelines on Cyclones

• Early Warning System: IMD has operationalized the Cyclone Warning Dissemination System
• To analyze Cloud aerosol interaction an Aircraft Probing of Cyclone (APC) facility is used
• National Disaster Communication Infrastructure is encouraged and commissioned by state disaster management authorities
• Lifeline infrastructure in coastal areas needs structural stability, multipurpose cyclone shelters and livestock mounds , all-weather highways connecting habitations to these shelters
• Flood inundation management and regulation plans are put in action
• Saline embankments and coastal bio-shields are built to block salinity.

Mitigation and Challenges

• Implement appropriate structural and non-structural solutions to lessen the effects of cyclones
• Enhancing DRM capacity at the federal, state, and local levels for risk mitigation
• improved early warning dissemination systems
• strengthened local community response capacity
• improved access to emergency shelter and evacuation
• improved protection against windstorms, flooding, and storm surge in high areas.

Integrated Coastal Zone Management Project (ICZMP)

• The project assists the Government in building the national capacity for implementation of a comprehensive coastal management approach in the country
• Capacity Building mapping, delineation and demarcation of the hazard lines, and delineation of coastal sediment cells
• Piloting ICZM approaches in Gujarat and Orissa