Weather

Saharan Dust Plume May Cause Minor Respiratory Problems, Suppress Hurricanes and Cause Spectacular Sunsets

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June 23, 2020

Persistent east to west winds blow Saharan desert dust over the Atlantic Ocean every year. A massive plume of dust this week is exceptionally large and traveling a long distance, easily reaching the Caribbean and forecast to soon arrive in North America.

Scientifically, the particulate matter carried by such plumes is called aerosols. Other aerosols that can travel thousands of miles include sulfate aerosols from volcanoes or air pollution and black carbon aerosols from forest fires. Sea salt is another important aerosol, but typically it does not travel as far as dust, sulfate particles, or black carbon.

A massive plume of Saharan dust is visible over the Caribbean in this NOAA satellite image.

One way scientists measure the presence of aerosols in the atmosphere is by measuring the Aerosol Optical Depth (AOD). Such measurements use satellite imagery or ground sensors to measure the amount of particulate matter above a given location on Earth. The map below animates the motion of aerosols this week, depicting dust as a red plume. Click on the link to watch the animation.

This animated map from NASA’s Scientific Visualization Studio forecasts the flow of the Saharan dust plume. Link: https://svs.gsfc.nasa.gov/4582

So what does this massive plume of Saharan dust mean for us? We may see three impacts for areas in the southeast U.S. and along the Gulf Coast.

1) Minor respiratory problems

Most of the dust reaching the U.S. will be found in the middle- or upper-levels of the atmosphere and will be too high to directly affect humans. However, if dust settles lower in some areas it could cause problems for people with pre-existing respiratory issues. Keep tabs on local forecasts and advisories from the National Weather Service; they will issue advisories if air quality deteriorates.

Thick dust near ground level left residue and caused respiratory problems in the Caribbean earlier this week. Check out this before and after picture from Villalba, Puerto Rico, comparing dusty conditions this week compared to clear skies.

Clear (left) and dusty (right) picture from Villalba, Puerto Rico. Photo: Osvaldo Burgos.

2) Suppression of hurricane development

Hurricanes need a moist atmosphere to convert warm sea water into fuel for development. Dust plumes of Saharan air come from a source region that is hot and dry. Typically, such dry air is prevalent at the middle and upper levels of the atmosphere, essentially choking off hurricane development. However, keep in mind that the heart of the Atlantic hurricane season runs from late July through early October, and the impact of these plumes are relatively short-lived. Scientific consensus still points towards an active Atlantic hurricane season.

Tropical Cyclone Narelle encountered a dust plume west of Western Australia in 2013. Dust is usually found in a dry layer that chokes off hurricane development. Photo: NASA/NOAA.

3) Beautiful, and unusual, sunrises and sunsets

The dust plume was so thick in parts of the Caribbean earlier this week that the particulate matter essentially blocked out the sunlight and even left residue on some surfaces. That’s some thick dust!

The particles should dilute somewhat before reaching the U.S., however, and the presence of thick dust at ground level is unlikely. Most of the dust that reaches the U.S. should be found in the middle and upper levels of the atmosphere.

Saharan dust makes the circular sun visible and creates a pastel sunset of yellows and oranges in Southeast Texas on June 28, 2019. Photo: Hal Needham.

In some areas, the dust may be thick enough to block out the sun or make the circular edge of the sun visible around dawn and dusk. In other areas, the high dust particles will scatter sunlight, causing spectacular sunrises and sunsets. I took the picture above on June 28, 2019, capturing the effect of Saharan dust on a Texas sunset. Note the circular edge to the sun and pastel yellow and orange colors in the sky.

The thickest part of this week’s dust plume will most likely arrive along the U.S. Gulf Coast or and southeastern states on this Wednesday and Thursday (June 24 and 25), so keep an eye to the sky for some sensational views!