A warming hole in the North Atlantic has an impact on the jet stream

According to a team of researchers, the North Atlantic Warming Hole (NAWH), a region of the North Atlantic Ocean, is dramatically affecting the North Atlantic jet stream in future climate simulations. .

Sea surface temperatures are expected to increase in most of the world's oceans as a result of global climate change. However, in an area of ​​rotating ocean currents just south of Greenland, there is an anomaly: colder sea surface temperatures have been documented in global climate model projections and observations.

"This is called a hole because there is a lack of warming," said Melissa Gervais, assistant professor of meteorology and atmospheric science at Penn State, who used the community land system model ( CESM) to study the impact of the NAWH on atmospheric circulation and mid-altitude jets. "We have found that this area of ​​the ocean is a very important place to force the jet stream that crosses the North Atlantic Ocean.

The researchers published their results in the Climate Journal.

The development of the NAWH is linked to the slowdown of the Southern Tidal Turning Circulation, a vast system of ocean currents that carry hot water from the tropics to the North Atlantic Ocean, and would be caused by an influx of freshwater from melting Arctic sea ice.

Previous research by Gervais and his team has shown that this increase in fresh water to the ocean alters circulation patterns and leads to cooling of the surface.

"With the melting of sea ice in the Arctic, more and more fresh water is pouring into the Labrador Sea, resulting in a reduction in deep convection," said Gervais, who is also a co-recruiter of the Institute for CyberScience. "This is changing the ocean circulation, allowing it to cool down in this region south of Greenland."

This cooling pattern, relative to the global average increase in sea temperature, is expected to become larger and more apparent relative to the variability of the internal ocean as the 21st century progresses.

"These changes in OHS patterns result from changes in ocean circulation and could have a significant impact on the atmospheric circulation and trajectory of storms in the North Atlantic," said Gervais.

Jet streams, high-altitude wind currents above the Earth, carry air masses and determine weather conditions. The relationship between climate change and jet flows is complex and understanding the potential impact of climate change on jet flows is critical to understanding changes in weather patterns and storm patterns.

"With climate change, we have some ideas on how the jets will change – in general, we expect a change in polarity and a longer jet to the east," Gervais said. "At the present time, there is a kind of fierce struggle between the impacts of the tropics and the impacts of the Arctic." So, these two things are competing for mobility. where the jet is located. "

Most climate models seem to agree that the jet stream of the Pacific will move the poleward, but there is great variability in the forecast for the Atlantic, said Gervais.

In order to study the impact of the development of NAWH on the jet stream, the team conducted a series of experiments on large ensemble atmospheric models in the CESM with the prescribed SST and sea ​​ice levels over three different periods.

"We did three simulations," said Gervais. "One with the current warming conditions, one where the temperature of the ocean was increased to fill the warming hole, and the other where its size was twice as deep, to simulate more fresh water from melting ice. "

Their results indicate that NAWH plays an important role in the changes of the atmospheric circulation at medium altitude in the climate simulations of the model.

"We found that it's really very important for this region," Gervais said. "The NAWH seems to lengthen the jet even further and move it a little further north, instead of just thinking about the influence of the tropics and the Arctic amplification on the jet, we have to also think of how this warming hole will influence These local changes in the North Atlantic aircraft have a magnitude similar to that of the total response to climate change in the region, indicating that the warming hole of the North Atlantic could be an important additional factor in the fight against the rope on medium-altitude traffic, received little attention. "