Airborne visitors from Sahara enroute
By Skip Rigney
Trillions of overseas visitors will be arriving in Pearl River County during the upcoming week. Most will only be passing through, but a few will be sticking around for the long-term.
Despite their large numbers, most local residents probably won’t notice the newcomers. That’s understandable given that most of these drifters will be tiny. Really tiny. If you laid ten of them side by side, they could sit on the edge of a piece of paper.
Not only are they too small to be seen individually with the unaided human eye, most of these travelers will stay suspended in the air thousands of feet above us.
Although an expected increase in clouds and showers in the upcoming week will tend to mask their presence even more, the ability of these little globetrotters to scatter specific frequencies of sunlight may cause skywatchers to notice a milky, haziness during the brightest daylight, or more vivid oranges and reds near sunset.
These floating journeyers are dust particles from Africa. Strong east winds have been blowing across the Sahara Desert during the last couple of weeks, lifting megatons of fine grains of sand and dust into the lower atmosphere. An enormous plume of airborne dust was clearly visible on satellite imagery as it emerged off the west coast of Africa. Since then the easterly trade winds that persistently blow across the Atlantic Ocean have been advecting the dust cloud several hundred miles each day.
According to predictions from a NASA aerosol dispersion model, dust concentrations are likely to begin increasing along the northern Gulf Coast on Wednesday with even thicker levels arriving by Thursday and into next weekend. You can see the latest NASA forecast by clicking “Animate” online at fluid.nccs.nasa.gov/wxmaps/chem2d/
Don’t jump to the conclusion that clouds of African dust are another sign that the year 2020 has gone off the rails. Multiple Saharan dust plumes travel across the Atlantic each year, especially during the summer. This one just happens to be especially large.
The dust particles are so small and lightweight that they can stay suspended for days, weeks, and even months. But, as the plume travels, particles do settle out into the ocean, onto the ground and other surfaces. Rain showers also help “wash” some of the dust from the air and onto whatever is underneath.
Given enough dust plumes over enough years, the impact can be enormous. In 2007 Daniel Muls of the U.S. Geological Survey and his fellow researchers presented evidence that African dust may have been a major contributor to soils on a number of Caribbean islands as well as in South America, central America, Mexico, and the southeastern United States. Perhaps most impressive was their conclusion that, “Soils on the Florida Keys and islands in the Bahamas appear to have developed mostly from African dust.”
Breathing dusty air is potentially an issue for people with underlying respiratory conditions. It’s too early to tell if the dust concentrations in our area will be high enough to cause significant air quality issues.
With every cloud, including dust clouds, there are silver linings. Not only might our sunsets be more colorful, Saharan dust over the Atlantic Ocean inhibits tropical storm formation.