A record-setting dust storm stretched from the Sahara Desert to the Caribbean in late June.
NASA/NOAA/Colin Seftor
In June, residents of Puerto Rico woke to a Sun shrouded in a thick haze, and everything outside seemingly coated in reddish dust. Little did they know the phenomenon was connected to winds swept up by the largest African dust storm on record—an event so massive, scientists have dubbed it “Godzilla”. These winds, researchers now report, were in turn triggered by a meandering jet stream that circles the planet farther north.
The new findings identify yet another way in which a warming Arctic might disturb the weather half a world away. The root cause of the extra-wavy jet stream is under fierce debate, but some scientists believe Arctic warming and declining sea ice are to blame for Godzilla’s far-reaching effects. “Arguably there is at least an indirect connection between climate change and this notable dust storm,” says Michael Mann, an atmospheric scientist at Pennsylvania State University who has studied how Arctic changes might influence summer weather further south.
The Godzilla storm was truly monster-size. Desert winds known as the harmattan set records, blowing at more than 70 kilometers per hour across northwest Africa. A plume of pink-tinted dust nearly as big as the continental United States drifted west across the Atlantic Ocean. It weighed nearly 24 million tons—enough to fill thousands of Olympic-size swimming pools, says Hongbin Yu, an atmospheric scientist at NASA’s Goddard Space Flight Center.
Such storms are annual events with far-reaching effects. The phosphorous-rich clouds fertilize trees in the Amazon. The tiny particles of dust can also pollute the air across the Caribbean, presenting a serious health hazard. And research suggests the dust clouds, by reflecting sunlight to space, cool the tropical Atlantic Ocean in a way that might dampen hurricanes.
African dust blown across the Atlantic Ocean dims the Sun over the port of Havana, Cuba. Levels of airbone hazardous particles were up to 10 times higher than World Health Organization thresholds.
YAMIL LAGE/AFP via Getty Images
But what happened this year was a surprise, both in its size and how it formed, says study leader Diana Francis, an atmospheric scientist at Khalifa University. Typically, the dust storms are driven by warm, moist air from monsoons on the southern edge of the Sahara that blows to the north. Based on data from satellites and weather stations, Francis and her colleagues found a different trigger for the 2020 storm: a large patch of high-pressure air parked over the northwestern edge of Africa starting on 14 June, she and colleagues report this month in Geophysical Research Letters. That triggered 4 days of record-strong winds that blew from the northeast, sweeping up vast amounts of dust and lifting it up to 6 kilometers into the air. There it encountered the westbound African jet stream, which was also strengthened by the high-pressure system. By 20 June, the first traces of the cloud reached the Caribbean.
The team also found that the high-pressure system came at the same time as the polar jet stream was meandering, dipping down to far lower latitudes than usual. Those atmospheric waves led to a string of alternating high- and low-pressure weather systems that encircled the Northern Hemisphere for several weeks in the summer, like beads on a necklace. The same phenomenon planted a high-pressure system in Siberia, helping to fuel record heat.
It’s not clear why the jet stream wavered and set off this so-called wave train of weather systems, Francis says. But some studies suggest Arctic warming, driven by the loss of sea ice, is to blame. Because the Arctic is warming faster than the rest of the world, a reduction in temperature differences between the far north and mid-latitudes may be making the jet stream less stable, Francis says.
In recent years, atmospheric scientists have focused on a weakened jet stream in winter, says Stephen Vavrus, an atmospheric scientist at the University of Wisconsin, Madison. That’s when the reduction in temperature differences tend to be most pronounced. But Vavrus, an early proponent of a link between a loss of sea ice and changes in winter weather, is intrigued by the idea that the same thing—driven by loss of sea ice or of snow cover on land—could be happening in summer. “There’s some evidence that suggests that the summer signal may be very much there,” he says.
Others caution it’s hard to pluck out connections in chaotic weather systems with enough confidence to say this dust storm is linked to Arctic warming. “I’m a little skeptical that it can be a major factor,” says James Overland, an atmospheric scientist at the National Oceanic and Atmospheric Administration’s Pacific Marine Environmental Laboratory.
The Godzilla storm also raises questions about whether more African dust really dampens Atlantic hurricanes, says Amato Evans, an atmospheric scientist at the Scripps Institution of Oceanography who has studied such interactions. This year’s record dust clouds overlapped with a record Atlantic storm season that produced 30 named storms, says Evans, who collaborated with Francis on the dust storm study. “What the heck happened, and does dust really matter at all?”
Source: Science Mag