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A sign displaying the current temperature is shown after events were postponed due to high heat at the US Olympic Track and Field Trials on June 27 in Eugene, Oregon. (Yonhap News)

Extreme temperatures along the Pacific coast in western North America continue unabated, with a death toll that has already reached the hundreds.

A heatwave warning was also issued Thursday for Seoul and other locations in South Korea, which is also situated in the Northern Hemisphere. Weather experts are not ruling out the possibility that South Korea could see the same kind of “heat dome” phenomenon responsible for the scorching temperatures in North America.

Instability resulting from atmospheric stagnation often causes rain showers. According to the experts, South Korea could experience a similar heatwave to the one in North America if the hot and humid North Pacific High remains stuck in the air over the Korean Peninsula.

Atmospheric stagnation, or “blocking,” is the phenomenon responsible for both the North American heatwave and the late rainy season on the Korean Peninsula. Blocking means that the flow of air has been literally blocked so that it remains stuck in one place.

People stay in the shade at Gwanbangjerim Forest in Damyang County, South Jeolla Province, on Thursday when a heat advisory was issued for Damyang County. (Yonhap News)

The “heat dome” phenomenon likewise results from a hot air mass being blocked.

“Blocking can happen at any time. What’s distinctive about the North American heat wave is how long it has persisted,” said Lee Hyun-soo, manager of climate prediction for the Korea Meteorological Administration (KMA).

“This is seen as being related to climate change, in that it’s difficult to predict when or where it might occur,” he said.

With the melting of glaciers around the Arctic and other phenomena associated with intensifying global warming, the jet stream that serves to contain cold polar air has weakened. With the weakening of that stream’s ability to move air in an east-west direction, north-south flows of air have become more active, resulting in blocking phenomena in unexpected regions.

“Atmospheric blocking is inevitably going to intensify as average global temperatures rise and temperature differences by latitude decrease as a result of climate change,” said Ho Chang-hoi, a professor of Earth and environmental sciences at Seoul National University and a specialist in atmospheric science.

“It’s the same principle as sediment settling when a river’s currents weaken. It’s a sign of how intense climate fluctuations have gotten,” he said.

The KMA said that the duration of the rainy season and intensity of high temperatures this year would be difficult to predict.

“The rainy season has gotten off to a late start due to abnormal weather,” Lee Hyun-soo said.

“It’s very difficult for us to predict whether we’ll be seeing a heat wave afterward, or whether the rainy season will continue for a long time like it did last year,” he added.

With air remaining stationary in North America and eastern Siberia to the northeast of the Korean Peninsula, this blocks off an outlet for air around South Korea, which is located in a westerly wind belt. That means that an expansion of the hot and humid North Pacific High air mass could result in warm air being caught over the peninsula.

Another possibility is that the jangma (rainy season) front located at the edge of the North Pacific High could persist over the peninsula for a long duration.

By Choi Woo-ri, staff reporter

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