In late June and early July 2024, parts of Florida and the Texas Gulf will experience one of the largest recorded Saharan Air Layers (SALs) as it drifts 5000 miles over the Atlantic to the U.S. Most of these "dust clouds" don't reach the U.S. coast, making this week's SAL even more unique.
SALs affect a broad range of conditions like air quality, plant fertilization, hurricane strength, and even spectacular sunsets. Here's a breakdown of what you should know about these naturally occurring phenomena.
How SALs Form and Affect Tropical Cyclones
SALs develop when strong winds sweep tiny sand and mineral particles off the surface of the Sahara, forming plumes that rise into the sky. Large thunderstorms over North Africa typically initiate the development of most SALs.
As a SAL crosses the Atlantic, it usually occupies a 2 to 2.5-mile-thick layer of the atmosphere, with its base starting about 1 mile above the denser marine air that hovers at the surface. Annually, the SALs (a new one is born every 3-5 days) contain upwards of 60 million tons of dust. The warmth, dryness, and strong winds that make up a SAL suppress tropical cyclone formation and intensification by removing the moisture they need to form.
Research also shows that the presence of small particles in the air suppresses winds. The drifting sand particles also absorb sunlight, stabilizing the air and helping cool water surface temperatures—a key factor in reducing the speed at which a storm intensifies.
Why Mid-Summer Hurricanes Aren't Usually The Strongest
SAL activity typically ramps up in late June and remains active through August. Once they dissipate in early September, their impact on storm formation and intensification dissolves, allowing the development of the strong tropical cyclones the U.S. East Coast has come to know well
Scientists track SALs using satellites. They appear as a milky white to gray shading, similar to a haze, in
satellite imagery. NOAA uses aircraft research missions to sample the SAL and better understand how it can impact tropical cyclones. They also use the information to help improve forecasts and explore the possibility of manually diminishing storm development by seeding the atmosphere with dust when SALs are off-season.
Additional SAL Benefits
In addition to helping suppress storm activity, SALs help ecosystems. The minerals in SALs work as natural fertilizers, as they are rich in iron and benefit phytoplankton and other marine life. When these minerals make landfall, they are deposited in the soil to help enrich it as well.
SALs also generate pretty sunsets. The sun's white light is composed of all the colors of the rainbow. Our sky is blue because gasses in the atmosphere naturally scatter blue hues (shorter wavelengths) while leaving the yellow, orange, and red hues (longer wavelengths) intact. Sunrises and sunsets take on yellow and reddish hues because the sunlight passes through more of the atmosphere before it reaches your eyes, and this condenses the longer wavelengths. Heavy dust in the atmosphere enhances this effect, leading to longer-lasting, more intense colors and vivid sunsets and sunrises.
Of course, the arrival of SALs does not help people with breathing issues or allergies. In the Canary Islands, closest to where SALs form, many residents have to stay indoors for several days as SALs pass over them at lower altitudes because the air quality is so poor.
However, for most U.S. East Coast residents, the presence of SALs in the atmosphere is welcome during Hurricane Season.
Sources: Nesdis, NASA, Daily Mail, Science, Weather.gov,
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