June 27, 2020
Winds routinely blow clouds of Saharan dust out of West Africa and across the Atlantic Ocean in the summer. But the intensity and reach of a plume that left Africa in June 2020 was so great that it made internet meme makers buzz over a “Godzilla” cloud of dust. From the international space station, POT astronaut Doug Hurley described the large ribbon of dust as “amazing.” And as dust covered the Caribbean Sea and darkened the skies over several states in the southeastern United States, several meteorologists called the event “historic.”
We flew over this plume of Saharan dust today in the west central Atlantic. Amazing how big the area it covers! pic.twitter.com/JVGyo8LAXI
– Colonel Doug Hurley (@Astro_Doug) June 21, 2020
Such superlatives are backed by data. A preliminary analysis of Aerosol Optical Depth (AOD) measurements from NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) sensor showed a higher concentration of dust in the atmosphere over the Atlantic Ocean on June 20 than any other day since 2003. AOD is a unitless measurement of how much light prevents airborne particles from traveling through the atmosphere. A few days later, a land-based AERONET sensor at Ragged Point, Barbados, recorded the highest AOD value of all time that the site has recorded since 1996.
The feathers in June 2020 spanned thousands of kilometers. When the leading edge reached Puerto Rico and the skies turned a hazy yellowish gray, the beaches closed and air quality plummeted. “This is the most important event in the last 50 years,” Pablo Méndez-Lázaro, a scientist at the University of Puerto Rico, told the AP. “Conditions are dangerous on many islands in the Caribbean.” Méndez-Lázaro is working on a NASA applied science project to develop an early warning system for poor air quality in the region.
June 2 to 23, 2020
The image sequence above, based on data from NASA’s Goddard Earth Observation System (GEOS) modeling system, shows pulses of Saharan dust at one-week intervals as they crossed the Atlantic Ocean. Apart from Cape Verde, which is regularly covered with dust, the Caribbean islands were some of the most affected places. When the plume reached the United States, the Environmental Protection Agency reported on June 27 that levels of fine particles (PM2.5) had risen enough to reach “unhealthy levels” (between 151-200 on the air quality index) in Florida, Texas, and Georgia.
The data in the transect below reveals the height of the dust over the Dominican Republic as observed by the Nidar-Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument on the CALIPSO satellite on June 23, 2020. Reaching approximately 4 kilometers (2.5 miles) ), the top of the plume was a little higher than most; There was also a lot of dust at 1 kilometer or less (0.6 miles). As dust crosses the ocean, the largest particles fall first, leaving behind mainly the finest and smallest, which are especially problematic for human health.
June 23, 2020
Air pollution experts are not the only specialists who closely follow this event. Meteorologists track dust storms because dry, dusty air can inhibit cloud formation and prevent hurricanes. Infectious disease researchers observe them because the dust columns can be vectors of viral and bacterial diseases. And climate scientists study dust because large events can absorb enough light to affect Earth’s radiation budget.
Others will pay attention to the impacts on the oceans. “In waters with limited nutrients, iron and other nutrients in the powder can trigger phytoplankton blooms with wide-ranging effects,” said Hongbin Yu, a scientist at NASA’s Goddard Space Flight Center. Phytoplankton is central to marine food webs and plays an important, albeit poorly understood, role in the carbon cycle. “In this case, I don’t expect to see much of a response from the Gulf of Mexico, which already has a lot of nutrients. But we could see a major response in a few weeks if enough dust passes over Central America and ends up in the most nutrient-limited waters of the eastern Pacific. “
Similarly, outbreaks of Saharan dust can play a key role in fertilizing the nutrient-poor soils of the Amazon rain forest in winter and spring. However, Yu said that seasonal wind patterns generally carry most of the dust from summer events north of the Amazon rainforest and into the Caribbean.
Images from Joshua Stevens’ NASA Earth Observatory, using GEOS-5 data from NASA’s GSFC Global Modeling and Assimilation Office and data from the CALIPSO team.
