Saharan Dust Explained: Africa, Caribbean To USA

Saharan Dust Explained From Transport To Deposit

Saharan Dust Explained: Africa, Caribbean To USA – (CNN)The much-anticipated Saharan dust plume is now making its more than 5,000-mile trek across the Atlantic to the United States.

The thick dust is clearly visible on satellite imagery, too. You can make it out by the brown sheen spreading off the African coast. It’s so dense it’s making it almost hard to tell where the continent ends and the ocean begins!

Forecast models call for this swath of dust, straight from the Saharan Desert and carried by the east-to-west Trade Winds, to arrive in the Southeast US beginning on Wednesday of this week.

If you haven’t heard your friends talking about this “mysterious” Saharan dust plume supposedly adding yet another layer to 2020, then you’ve certainly seen it all over social media this past week. It’s the only thing people are talking about in the world of weather.

This Saharan dust plume blowing across the Atlantic Ocean from Africa is nothing new, or even special to 2020. In fact “large plumes of Saharan dust routinely track into the Atlantic Ocean from late spring into early fall.

Every so often, when the dust plume is large enough and trade winds set up just right, the dust can travel thousands of miles across the Atlantic and into the US.” CNN Meteorologist Haley Brink said.

These dust plumes actually happen often during hurricane season. Saharan dust can also impact you in several ways once it reaches land. Some of these impacts can be felt, while some are seen.

Here’s the top 3 ways you’ll notice next week’s Saharan dust here in the US.

A difference in the sky

One of the first things you’ll notice when the Saharan dust layer arrives is that your typical blue sky will have more of a milky haze to it. That milky haze is the Saharan dust! Those tiny dust particles lofted tens of thousands of feet in the air do a great job of scattering the sun’s rays at dusk and dawn, too, which gives way to stunning sunrises and sunsets.

So, grab those cameras!

Less tropical activity in the Atlantic

The Saharan dust to a hurricane is nothing more than extremely dry air. Hurricanes hate dry air! A hurricane needs a hot, humid and calm environment. As long as the Saharan dust is around … it’s likely you’ll see the National Hurricane Center watching fewer areas in the tropics.

Dust plume allergies

The tiny dust particles that give way to beautiful sunrises and sunsets and help suppress hurricane development don’t always stay at 30,000 feet. Sometimes particles can make their way to the surface, greatly affecting those with sensitive allergies.

If you find yourself reaching for a tissue this week — or your iPhone to post yet another awesome sunset pic to Instagram — thank the Saharan dust.

Video: Saharan Dust Plume

Saharan Dust Transport and Deposition

Millions of tons of mineral dust are transported from the African continent towards the Atlantic Ocean every year, with several direct and indirect effects on global climate.

CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) measurements between 2007 and 2013 show that, annually, 182 Tg of African dust leaves the African continent towards the Atlantic Ocean, 132 Tg reaches 35◦ W, and 43 Tg reaches as far west as 75◦ W (Yu et al., 2015). Approximately 140 Tg is deposited in the Atlantic Ocean between 15 and 75◦ W and 10◦ S and 30◦ N.

Atmospheric mineral dust affects the atmosphere’s radiation budget by scattering and absorbing incoming and reflected solar radiation, and changes cloud properties by acting as cloud condensation nuclei.

Climatic effects are largely determined by particle characteristics, including particle size, particle shape, chemical and mineralogical composition, and cloud cover and the albedo of the underlying surface. Large particles in the lower atmosphere may have a warming effect on earth’s climate by absorbing reflected (longwave) radiation.

By contrast, small particles in the higher atmosphere may have a cooling effect, by reflecting incoming solar (shortwave) radiation. Moreover, dust deposition enhances ocean carbon cycling by delivering nutrients that stimulate phytoplankton growth.

In turn, this leads to not only increased export fluxes but also faster transport of organic carbon to the deep ocean, as dust particles act as mineral ballast, depending on particle size, shape, and mineral density. Both have the potential to reduce atmospheric pCO2 levels.

The distance over which mineral dust is transported depends on the transporting winds and particle characteristics, including size, shape, and density, which determine settling velocities. Rounded quartz and feldspar particles have a greater settling velocity than platy clay minerals and are therefore deposited closer to the source.

Saharan dust is transported with the trade winds year-round, from the northwestern Sahara to the eastern Atlantic Ocean. During winter, the Harmattan trade winds prevail, transporting dust from the central Sahara at altitudes between 0 and 3 km.

In summer, when the larger land–sea temperature contrast results in large convective cells over the African continent, dust is emitted from the Sahara and Sahel. During transport towards the Atlantic Ocean, cool marine air blows in the opposite direction and lifts the warm, dusty air high up in the atmosphere.

This Saharan Air Layer (SAL) is confined between two inversion layers, at 1 and 5 km height. Due to the latitudinal movement of the ITCZ (Intertropical Convergence Zone), the dust cloud
over the Atlantic Ocean also migrates seasonally, shifting northward (10–20◦ N) in summer and southward (0–10◦ N) in winter. Read full PDF Here