‘Heat dome’ over North-West India

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    In Context

    • According to recent reports, the ‘Heat dome’ over North-West India may retract.

    More about the heat Dome:

    • About:
      • A heat dome occurs when the atmosphere traps hot ocean air like a lid or cap.
    • How does it form?
      • Extreme heat waves have become more frequent in recent decades. Sometimes, the scorching heat is ensnared in what is called a heat dome. 
      • This happens when strong, high-pressure atmospheric conditions combine with influences from La Niña, creating vast areas of sweltering heat that gets trapped under the high-pressure “dome.”
      • Correlation with jet streams:
        • Typically, heat domes are tied to the behavior of the jet stream, a band of fast winds high in the atmosphere that generally runs west to east.
        • Normally, the jet stream has a wavelike pattern, meandering north and then south and then north again. 
        • When these meanders in the jet stream become bigger, they move slower and can become stationary. That’s when heat domes can occur.

    • Outcomes:
      • Human body:
        • A heat dome can have severe impacts on people because the stagnant weather pattern that allows it to exist usually results in weak winds and an increase in humidity
          • Both factors make the heat feel worse – and become more dangerous – because the human body is not cooled as much by sweating.
      • Heat illnesses and deaths:
        • The high humidity also reduces the amount of cooling at night. Warm nights can leave people without air conditioners unable to cool off, which increases the risk of heat illnesses and deaths. 
        • With global warming, temperatures are already higher, too.
          • One of the worst examples of the impacts from a heat dome with high temperatures and humidity in the U.S. occurred in the summer of 1995, when an estimated 739 people died in the Chicago area over five days.
    • Heat Waves:
      • It is a period of unusually hot weather that lasts for more than two days.
      • The heatwaves can occur with or without high humidity and have the potential to cover a large area, exposing a high number of people to hazardous heat.
    • Impact of Climate Change:
    • Scientists believe that the heat waves occurring today are more likely to be a result of climate change for which humans are responsible.
    • A small increase in the Earth’s average temperature can dramatically impact climate extremes, both hot and cold, increasing their chances of occurring exponentially.
    • Extreme heat events are occurring more frequently with more severity, and therefore they will likely push the average temperatures higher for years to come.
    • If greenhouse gas emissions are not significantly curtailed, the coldest and warmest daily temperatures are expected to increase by at least 5 degrees F in most areas by mid-century rising to 10 degrees F by the late century.

    Cyclones and anticyclones

    • Cyclones and anticyclones are regions of relatively low and high pressure, respectively. 
      • They occur over most of Earth’s surface in a variety of sizes ranging from the very large semipermanent examples described above to smaller, highly mobile systems.
    • Cyclone:
      • Cyclone is any large system of winds that circulates about a centre of low atmospheric pressure in a counterclockwise direction north of the Equator and in a clockwise direction to the south. 
    • Anticyclone:
      • Anticyclone is any large wind system that rotates about a centre of high atmospheric pressure clockwise in the Northern Hemisphere and counterclockwise in the Southern. 
        • Its flow is the reverse of that of a cyclone.
      • Effects:
        • Effects of surface-based anticyclones include clearing skies as well as cooler, drier air. Fog can also form overnight within a region of higher pressure.

    Western Disturbance (WD)

    • It is an extra-tropical storm that originates in the Mediterranean region.
    • The disturbance travels from the “western” to the eastern direction and  gradually travels across the middle-east from Iran, Afghanistan and Pakistan to enter the Indian subcontinent.
      • Disturbance means an area of “disturbed” or reduced air pressure
        • Equilibrium exists in nature due to which the air in a region tries to normalize its pressure.
      • Western disturbances are more frequent and stronger in the winter season.
    • Outcome:
      • In the case of Indian subcontinent, moisture is sometimes shed as rain when the storm system encounters the Himalayas.
      • Western disturbances are important for the development of the Rabi crop which includes the locally important staple wheat. 

    Source: BL