Is Arctic Warming Behind a Monster Saharan Dust Storm?https://phys.org/news/2020-12-arctic-monster-saharan-storm.htmlThe June 2020 dust storm set records in terms of its geographic size and its aerosol optical depth—essentially a measure of its thickness determined by the ability of satellites to see through it. It reached an altitude of 6,000 meters (19,600 feet). In certain locations over the Atlantic Ocean, its thickness was double what had ever been recorded during the month of June during the history of the satellite record, which dates back to 1995.
The researchers analyzed what made it happen in a study appearing today in the journal
Geophysical Research Letters.Evan, lead author Diana Francis of Khalifa University of Science and Technology in the United Arab Emirates, and colleagues attributed the dust storm's magnitude to conditions set up by the development of a type of high-pressure system called a subtropical high off the coast of the Sahara. This increased the north-south pressure gradient over West Africa leading to record-strength, persistent northeasterly winds. The intensification of the northeasterly winds over the Sahara generated continuous dust emissions over several days in the second half of June 2020.
The researchers found that the subtropical high was embedded in a circumglobal wavetrain, a chain of wind patterns that extended around the planet, and was present in the Northern Hemisphere for most of June 2020.
This wavetrain may have been caused by record-low Arctic sea ice extent observed in June 2020 as well. The warming of the Arctic region is believed to be altering the course of wind patterns in the mid-latitudes and subtropics and causing severe weather events, though there is controversy among scientists about this concept.
"The development of the subtropical high off the African coast had a deterministic role in both dust emissions and rapid westward transport of the airborne dust across the tropical Atlantic," said Francis. "The clockwise circulation associated with the high, intensified the African Easterly Jet, a jet stream present over the Sahara around five kilometers (3.2 miles) in altitude, which rapidly transported the dust towards the Caribbean and southern United States."
The study also touches on a controversial topic within the science community.
Though not the main focus of study, the wavetrain pattern that set the Godzilla dust storm in motion looked very similar to one observed in 2010 when sea ice in the Arctic Ocean was substantially diminished, Francis' team noted.
"As the Arctic sea-ice cover was rather low in June 2020, around the lowest on record in the period of satellite observations, it may have contributed to the observed large-scale anomaly pattern," the study concludes. "Thus, if such patterns become more common in a warmer world, it is plausible that these extreme dust outbreaks will increase in frequency in the future."Diana Francis et al.
The Atmospheric Drivers of the Major Saharan Dust Storm in June 2020,
Geophysical Research Letters (2020)
https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020GL090102
