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.
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, Abu Dhabi. 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.