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The North Atlantic warming hole affects the jet stream

  North Atlantic warming hole affects the jet stream
Floating iceberg in Labrador Lake south of Greenland. Picture credits: Melissa Gervais / Penn State

The North Atlantic Warming Well (NAWH), a region of reduced warming in the North Atlantic, is significantly impacting the North Atlantic jet current in future climate simulations, according to a research team.

Sea Surface Surface Temperatures (SSTs) are expected to increase in most oceans as a result of global climate change. However, in an area with rotating ocean currents south of Greenland, there is an anomaly in which colder sea surface temperatures have been documented in both global climate model projections and in observations.

"It is called a hole because of a lack of warming," said Melissa Gervais, Assistant Professor of Meteorology and Atmospheric Research, Penn State, who used the Community Earth System Model (CESM) to study the effects of NAWH on atmospheric circulation and to investigate midlatitude jets. "We have found that this region of the ocean is a really important place to push the jet stream through the North Atlantic."

The researchers published their findings in the Journal of Climate ] The development of the NAWH is associated with a slowdown in Atlantic meridional overturning circulation, a large system of ocean currents that carry warm water from the tropics to the north leading to the North Atlantic, and is likely to melt Arctic sea ice caused by an influx of freshwater.

  North Atlantic Heath Warming Affects Jetstream
Floating iceberg in Labrador Lake, south of Greenland. Picture credits: Melissa Gervais / Penn State

Previous research by Gervais and her team has shown that this increase in freshwater in the ocean changes circulation patterns and leads to surface cooling.

"With more Arctic sea ice, more fresh water is melting into the Labrador Sea leading to a reduction in deep convection," said Gervais, who is also co-hire of the Institute for CyberScience. "This changes the ocean current so that it can cool down in this region south of Greenland."

It is predicted that this cooling pattern will become larger and more pronounced relative to the global average SST increase compared to the inner ocean variability as the 21st century continues.

"These changes in SST patterns occur as a result of changes in ocean circulation and could have a significant impact on the atmospheric circulation and the North Atlantic track in the future," Gervais said.

High-altitude winds, which flow over the earth, transport air masses and drive the weather. The relationship between climate change and jetstreams is complex, and understanding the potential impact of climate change on jetstreams is critical to understanding changes in weather patterns and storm paths.

  The North Atlantic warming hole affects the jet stream
The Greenland coast of the Knorr WHOI research vessel. Picture credits: Melissa Gervais / Penn State

"With climate change, we have some ideas of how the jets will change, and we generally expect a shift of poles to the east and an extension of the jet to the east," Gervais said. "At the moment it's a kind of tug-of-war between the tropics and Arctic influences, these two things are competing to move the jet's location."

Most climate models seem to agree with the Pacific Jet Power will change, but the predictions for the Atlantic are very different, Gervais said.

To investigate how the development of NAWH affects jet flow, the team conducted a series of atmospheric large ensembles through experiments in the CESM with prescribed SST and sea ice values ​​over three different time periods.

"We did three simulations," Gervais said. "One with current conditions for the warming holes, one in which the water temperature was increased to fill the reheat hole, and one where the size was twice as deep to simulate more fresh water from melting ice sheets."

Your Results Show That NAWH plays an important role in atmospheric circulation changes in the model's future climate simulations.

"We have found that this is really important for this region," said Gervais. "The NAWH seems to extend the jet even further and shift it to the north, so instead of just thinking about how the tropics and Arctic reinforcement affect the jet, we need to think about how this heat hole will affect these local changes in the North Atlantic Jet is similar in magnitude to the full response of climate change in the region, suggesting that the North Atlantic warming hole could be an important additional factor for the tidal drag of the midlatitude circulation has received little attention. "

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Further information:
Melissa Gervais et al., Effects of the North Atlantic Warming Hole in Future Climate Projections: Mid-atmospheric Circulation and the North Atlantic Jet, Journal of Climate (2019). DOI: 10.1175 / JCLI-D-18-0647.1

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Warming hole in the North Atlantic influences the jet stream (2019, April 15)
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