Heat Dome

Context: 

Parts of Canada and USA are reeling under severe heat wave caused due to a heat dome. 

What is a heat dome?

According to The National Oceanic and Atmospheric Administration (NOAA), a heat dome occurs when the atmosphere traps hot ocean air like a lid or cap.

• Heat dome is more likely to form during La Niña years like 2021, when waters are cool in the eastern Pacific and warm in the western Pacific.
• The phenomenon begins when there is a strong change (or difference) in ocean temperatures. In the process known as convection, the temp difference causes more warm air, heated by the ocean surface, to rise over the ocean surface.
• That temperature difference creates winds that blow dense, tropical, western air eastward. Eventually that warm air gets trapped in the jet stream—a current of air spinning counterclockwise around the globe—and ends up on the U.S. West Coast, resulting in heat waves.
  • A heat wave is a period of unusually hot weather that lasts for more than two days. Heat waves 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 heat wave: So as long as the body is producing sweat, which is then able to evaporate quickly, the body will be able to remain cool even under high temperatures. But, there is a limit to this (a limit called the wet-bulb temperature) beyond which humans cannot tolerate high temperatures. Some heat-related illnesses include heat stroke, heat exhaustion, sunburn and heat rashes. Sometimes, heat-related illnesses can prove fatal.
  • Wet Bulb temperature: is the lowest possible temperature that a surface can reach by evaporative cooling (i.e. that a wetted surface can reach with air passing over it) in a given spot.
• Example: To understand what causes a heat dome, one should liken the Pacific ocean to a large swimming pool in which the heater is turned on. Once the heater is on, the portions of the pool close to the heat source will warm up faster and therefore, the temperature in that area will be higher. In the same way, the western Pacific ocean’s temperatures have increased in the past few decades and are relatively more than the temperature in the eastern Pacific.

Causes of Heat Dome: 

• This happens when strong, high-pressure atmospheric conditions combine with influences from La Niña. 
• This creates vast areas of sweltering heat that gets trapped under the high-pressure “dome“. 
• The main cause is a strong change (or gradient) in ocean temperatures from west to east in the tropical Pacific Ocean. 

Heat Wave:

• A heat wave is a period of abnormally high temperatures, more than the normal maximum temperature that lasts for more than two days.
  • Heat waves typically occur between March and June, and in some rare cases even extend till July.
  • Heat waves 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 on Humans (Wet-bulb temperature):

• As long as the body is producing sweat, which is then able to evaporate quickly, the body will be able to remain cool even under high temperatures.
  • Wet-bulb temperature (WBT) is a limit that considers heat and humidity beyond which humans can not tolerate high temperatures.
  • Temperatures beyond WBT can cause heat related illnesses including heat stroke, heat exhaustion, sunburn and heat rashes. Sometimes these can prove fatal.

Effects of Heat Dome:

• Those living without an air conditioner see the temperatures of their homes rising to unbearably high, leading to sudden fatalities.
  • The trapping of heat can also damage crops, dry out vegetation and result in droughts.
  • The sweltering heat wave will also lead to rise in energy demand, especially electricity, leading to pushing up rates.
  • The heat domes can also act as fuel to wildfires, which destroys a lot of land area in the US every year.

Are heat domes linked to climate change?

It’s challenging to link any one specific weather event with climate change, but over time the trend is showing longer-lasting, more intense heat.

• Climate change certainly influences hot weather: It is making heat more extreme and such extreme heat will occur more frequently.
• In Russia, cities as far north as the Arctic circle broke heat records this month.

Source: Indian Express