Tropical cyclones and temperate cyclones (extratropical cyclones) are complex atmospheric systems with distinct structures and characteristics.
1. Structure of Tropical Cyclones
Components and Characteristics:
Tropical cyclones are intense low-pressure systems that form over warm ocean waters near the equator. They are characterized by a well-defined center of circulation and organized bands of thunderstorms that spiral inward towards the center.
a. Eye:
- Eye: At the center of a mature tropical cyclone is the “eye,” which is a region of relatively calm and clear skies. The eye typically ranges from a few kilometers to tens of kilometers in diameter.
- Eye Wall: Surrounding the eye is the “eye wall,” which is a ring of deep convective thunderstorms with the strongest winds and heaviest rainfall in the entire storm. The eye wall is where the most intense winds and updrafts are found.
b. Rainbands:
- Rainbands: Spiral bands of thunderstorms extend outward from the center of the storm. These bands are characterized by heavy rainfall, gusty winds, and occasional tornadoes. Rainbands can extend hundreds of kilometers from the center of the cyclone.
c. Central Dense Overcast (CDO):
- Central Dense Overcast: Above the eye and eye wall, there is often a large area of thick clouds known as the CDO. These clouds are typically colder and taller than those in the rainbands and contribute to the overall intensity of the storm.
d. Outflow:
- Outflow: Tropical cyclones are fueled by the release of latent heat from condensation within the thunderstorms. This heat release creates a vertical motion that powers the storm. The upper-level outflow of air from the storm is essential for maintaining its structure and intensity.
e. Storm Surge:
- Storm Surge: When tropical cyclones make landfall, the low-pressure center and strong onshore winds can push ocean waters inland, causing a storm surge. This surge can lead to coastal flooding and inundation, especially in low-lying areas.
Example:
- Hurricane Katrina (2005): Katrina had a well-defined eye surrounded by a powerful eye wall with intense thunderstorms. Spiral rainbands extended far from the center, bringing heavy rainfall and strong winds to a wide area, causing catastrophic flooding in New Orleans and other parts of the Gulf Coast.
2. Structure of Temperate Cyclones (Extratropical Cyclones)
Components and Characteristics:
Temperate cyclones, or extratropical cyclones, form outside the tropics in regions of strong horizontal temperature gradients. They are responsible for much of the day-to-day weather variability in mid-latitudes.
a. Frontal Boundaries:
- Frontal Systems: Extratropical cyclones typically form along frontal boundaries where cold and warm air masses meet. There are three primary types of fronts associated with these cyclones:
- Warm Front: Where warm air rises over cold air, leading to stratus and nimbostratus clouds and prolonged precipitation.
- Cold Front: Where cold air advances and undercuts warm air, leading to cumulonimbus clouds and heavy showers or thunderstorms.
- Occluded Front: Where a cold front overtakes a warm front, lifting warm air aloft and producing widespread cloudiness and precipitation.
b. Low-Pressure Center:
- Central Low Pressure: Extratropical cyclones have a well-defined center of low pressure, often located along the intersection of the frontal boundaries.
c. Development:
- Cyclogenesis: Extratropical cyclones develop from wave disturbances along frontal boundaries, deepening as warm and cold air masses interact and create lifting mechanisms for cloud formation and precipitation.
d. Upper-Level Support:
- Jet Streams: The polar and subtropical jet streams provide upper-level support and steering currents for extratropical cyclones. The interaction between these jet streams influences the track and intensity of these storms.
Example:
- European Windstorms: These are examples of intense extratropical cyclones affecting Western Europe, characterized by well-defined frontal systems and strong winds. They bring heavy rainfall, storm surges, and occasionally snowfall to the region.
3. Cyclones in India
Tropical Cyclones:
- Bay of Bengal: Cyclones originating here impact the eastern coast of India and neighboring countries like Bangladesh and Myanmar. Examples include Cyclone Phailin (2013) and Cyclone Amphan (2020).
- Arabian Sea: Cyclones originating here affect the western coast of India and neighboring countries. Examples include Cyclone Nisarga (2020) and Cyclone Tauktae (2021).
Temperate Cyclones:
- Impact: Extratropical cyclones affecting India typically arrive from the west, bringing winter rainfall and occasional thunderstorms to regions like northern India and the Himalayan foothills.
Conclusion
The structure of tropical and temperate cyclones varies significantly based on their formation mechanisms and environmental conditions.
