Geophysical Phenomena

Introduction:

Cyclones are intense circular storms that originate over warm tropical oceans and are characterized by low pressure at the center, strong winds, and heavy rainfall. The formation and intensity of cyclones are influenced by several climatic factors such as sea surface temperature, atmospheric moisture, and wind patterns.

Factors Contributing to Cyclone Formation

1. Warm Sea Surface Temperature (SST):
   • Cyclones typically form in tropical regions where sea surface temperatures exceed 26.5°C. Warm water provides the necessary heat and moisture, which leads to the formation of convective clouds and the development of a low-pressure system.
   • Recent Example: The rise in sea surface temperatures due to climate change is linked to an increase in the intensity of cyclones. In 2023, Cyclone Biparjoy in the Arabian Sea intensified rapidly due to abnormally high SST.
2. Atmospheric Moisture:
   • High levels of moisture in the atmosphere, especially in the middle and upper troposphere, contribute to cyclone development by fueling convection. This moisture is crucial for the condensation process, which releases latent heat and powers the cyclone.
   • Recent Example: The Indian Ocean witnessed more intense cyclones in recent years due to enhanced moisture levels, particularly during the post-monsoon period.
3. Coriolis Force:
   • The Coriolis force, caused by the Earth’s rotation, helps cyclones spin and maintain their structure. The force is weakest at the equator and strengthens as one moves toward the poles, which is why cyclones do not form near the equator.
4. Low Wind Shear:
   • Low vertical wind shear (difference in wind speed and direction with height) allows cyclones to grow. High wind shear can disrupt cyclone formation by dispersing the heat and moisture required for intensification.
   • Recent Example: Cyclone Fani (2019), which struck India, was able to sustain its intensity because of favorable low wind shear conditions in the Bay of Bengal.
5. Pre-existing Disturbance:
   • A low-pressure area or tropical disturbance is necessary to kick-start the formation of a cyclone. Without an initial disturbance, cyclonic activity cannot begin.

Climatic Conditions and Cyclone Intensity

1. Ocean Heat Content:
   • The deeper the layer of warm water, the more energy is available for cyclones to intensify. This is referred to as ocean heat content (OHC). Higher OHC results in stronger cyclones with greater intensity and destructive potential.
   • Recent Example: Cyclone Tauktae (2021) rapidly intensified due to extremely high ocean heat content in the Arabian Sea, which has been linked to global warming.
2. Rising Sea Levels:
   • Rising sea levels, caused by melting ice caps and thermal expansion, increase the destructiveness of storm surges associated with cyclones. Higher storm surges lead to more coastal flooding and damage.
   • Recent Example: During Cyclone Amphan (2020), higher sea levels along the Bay of Bengal’s coastline exacerbated flooding in eastern India and Bangladesh.
3. Climate Change and Intensification:
   • Climate change is leading to more frequent and intense cyclones due to rising global temperatures and increasing sea surface temperatures. Studies indicate that the proportion of very severe cyclonic storms (VSCS) has increased in recent decades.
   • Recent Example: The 2020 cyclone season in the North Indian Ocean was particularly severe, with multiple intense cyclones like Amphan and Nivar, attributed to warming oceans and altered wind patterns.

Conclusion:

The interplay between oceanic and atmospheric conditions largely determines the formation and intensity of cyclones. With climate change altering many of these factors, cyclones are becoming more frequent and intense, posing increasing challenges for coastal communities. Effective mitigation and adaptation strategies are crucial to minimize the impact of these climate-driven disasters.