Agri Business

‘Heat dome’ in US-Canada and ‘heat wave’ over N-W India: More than just hot air

Thiruvananthapuram | Updated on July 02, 2021

Two phenomena half a world apart are entirely different in origin

The ‘heat dome’ over the Pacific North-West that broke all-time temperature records over adjoining US-Canada and the ongoing ‘heat wave’ over North-West India are distinguishable only insofar as they feature similar geographical bearings replete with a common but inevitable ‘heat’ denominator.

The causal links to either phenomenon on two lands half a world apart cannot be more starkly different, says GP Sharma, President, Meteorology and Climate Change at leading private forecaster Skymet Weather. The underlying motion of air/winds is what sways it, he told BusinessLine.

Totally different cases

“These are two totally different. You just cannot connect one with the other. You normally compare two things when they share a single or common platform. Or consider this. On our side the heat is more of an advected thing (horizontal motion of hot air from across the border in Pakistan),” Sharma said.

Advection is confined to the lower levels of the atmosphere. As against advection of heat, the Pacific North-West sees initially convection or upward movement of air with the heat getting trapped in the higher levels. So, the heat dome represents heat trapped within an envelope in the higher levels.

The heat dome represents a high-pressure cell also known as a ‘blocking high’ since it restricts free movement of air in the atmosphere which is otherwise very dynamic with no barriers. High-pressure areas witness sinking motion of air (unlike in low-pressure areas when the air moves up and cools).

Sinking motion of air

The sinking motion leads to the even more pressure and therefore heat, which has now broken a 1,000-year-old record variously across Portland, Seattle and Washington in the US and British Columbia in Canada. There are multiple factors working in tandem to bring this type of weather there, Sharma said.

The movement of air is lateral or horizontal over Pakistan and adjoining North-West India while it is vertical or upward movement initially over the Pacific North-West and adjoining US-Canada. “So, we can see that the phenomenon in the Pacific North-West originates from the ocean unlike the case here.”

This is because of the temperature gradient over the ocean (normally we talk about the pressure gradient, which drives the monsoon). The larger the gradient, more the upward motion of air from the ocean. Certain atmospheric features in the higher levels over North-West Pacific traps the heat brought up by convection.

Two different latitudes

“Basically, we are two geographies belonging to two different latitudes. While we are in the tropical (lower) latitudes, that part of the US-Canada belongs to much higher latitudes, closer to the polar regions. This straight away rules out any comparison of weather.”

Also, weather patterns and the governing systems are totally different, Sharma said. There are typical terminologies associated with weather systems such as ‘cut-off lows’, ‘cold poles’ or ‘blocking highs’ in those higher latitudes which don’t normally formally in the tropics, he explained.

There is a subtle difference here in that during the winter the jet stream descends over India and sends out western disturbances, these terminologies make better sense. There’s hardly any western disturbance activity now; else, the monsoon would have come sooner to Delhi by interacting with it.

Published on July 02, 2021

Follow us on Telegram, Facebook, Twitter, Instagram, YouTube and Linkedin. You can also download our Android App or IOS App.

This article is closed for comments.
Please Email the Editor

You May Also Like