The Southeast US is getting spoiled with some evening color, all thanks to dust from 5,000 miles away.
The trade winds — westward moving winds in the upper atmosphere — are picking up dust from the Sahara Desert in northern Africa, lofting it over the Atlantic Ocean and filling the skies from Florida to East Texas.
While the dust may not be noticeable during the day, its presence in the atmosphere is creating some spectacular sunsets by scattering the evening rays of light.
Since the start of summer, social media feeds have been filled with vibrant red-orange images from the Gulf Coast states.
Fertilizing soil and impairing breathing
For thousands of years, winds have carried dust from Saharan Africa across the Atlantic and into the Americas, with as much as 40 million tons of dust transported in just one week, NASA says.
Good and bad can come from these dust transports, known as the Saharan Air Layer. The air mass, for instance, can fertilize soils in the Amazon River Basin. But it can also spark outbreaks of toxic algal blooms and impair air quality around the Gulf of Mexico, NASA says.
The dust now is hovering at 5,000 to 20,000 feet in the atmosphere over Gulf Coast states. So, people with sensitive respiratory conditions should limit their time outside over the next couple days.
How dust helps color the evening sky
Besides those effects, the dust is enhancing the palette of the evening sky. Here’s why:
During the day, when the sun is highest in the sky, blue light is scattered more than other colors because it has a shorter wavelength in the spectrum of light. But in the evening, when the sun is low on the horizon, it has more atmosphere to shine its light through.
We see red and orange because they have longer wavelengths. When dust is high up in the atmosphere, the air is more dense, which enhances the scattering light rays, resulting in more vibrant shades of those colors.
Keeping tropical storms at bay
As it enhances sunsets, the plume of dust is also keeping things quiet in the tropics. Because the air is dry in the upper atmosphere and filled with particles, areas of low pressure in the Atlantic and Caribbean have a hard time organizing.
So, if this dust transport continues to be active during the peak of the Atlantic hurricane season, it could limit the number hurricanes that form before the season ends November 30..
For now, if you live in the Southeast US, enjoy the evening color over the next few days. Showers and thunderstorms will fizzle the dust out of the sky by the end of the week.