Context

Mumbai and Dubai experienced contrasting extreme weather occurrences triggered by an anticyclone.

Extreme Weather Events in Mumbai and Dubai

Heat Wave in Mumbai: The Konkan coast of India, especially the city of Mumbai, has been undergoing a humid heat wave characterized by intense humidity.

• Santa Cruz weather station in the city recorded a maximum temperature of 37.9 degree Celsius (°C) and had a high relative humidity of 55 per cent.
• Heat waves are particularly lethal when high temperatures combine with high humidity, which is commonly referred to as a wet bulb. 
• In such conditions, sweat from the human body isn’t able to evaporate, failing to stabilize the body temperature, which could ultimately cause heat stroke.

Floods in Dubai: Torrential rain accompanied by lightning inundated large areas of the city, causing flooding. 

• Other Emirati cities like Sharjah and Abu Dhabi received excess rainfall with the United Arab Emirates (UAE) receiving its highest rainfall in 75 years, when records began. 
  • Other countries in the region like Oman and parts of Saudi Arabia and Bahrain received excessive rainfall, with 18 people killed in Oman due to flash flooding.
• Reason Behind Extreme Events: Both of these incidents were triggered by a vast anticyclone along with some localized weather phenomena, and further fuelled by general warming and increased moisture levels in the atmosphere.

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About Anticyclone

An anticyclone also known as a high pressure area is an area of high atmospheric pressure where winds blow in a downward sinking motion and in the process, compress and heat up.  This causes dry and hot weather. 

• Direction of Winds: The wind flows clockwise around it in the Northern Hemisphere, and counter-clockwise in the Southern Hemisphere. 
• Impact: The net result of the anticyclone is a large-scale heat dome with air sinking, compressing and warming. 

Characteristics of Anticyclones: 

• Season: Anticyclones can occur in both winter and summer with varying effects, but both are typified by low wind speeds due to a weak pressure gradient and stable conditions with no cloud.
  • Expanse: Anticyclones can be very large, typically at least 3,000 km wide which is much larger than depressions. 

Weather Condition Associated with Anticyclones

• Clear Skies: Anti-cyclones are associated with clear skies as the sinking air suppresses cloud formation.
• Calm Winds: The winds remain calm and gentle during an anticyclone, and there is almost no formation of clouds because here the air sinks rather than rises.
• Fog and Mist: Anticyclones can cause fog or mist to form, especially in low-lying or highly humid areas.
• Light Winds: Weak pressure gradients associated with anticyclones result in calm or light winds at the surface. 
  • From the high-pressure system’s center, the air tends to diverge outward, creating mild breezes or occasionally stagnant air.
• Blocking Weather pattern: They are generally related to large-scale and elongated heat waves but they also form a blocking pattern which doesn’t let other weather systems pass by and create conditions for extreme weather on their peripheries as well.

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