HOUSTON – It happens a few times every summer -- dust from the sands of the Sahara Desert in North Africa are carried on the wind, across the globe to Houston.
Here are a few things you should know about the phenomenon.
What causes it?
As the air heats up over the western reaches of the desert, it rises into the upper-level winds of the atmosphere, carrying fine particles of dust along with it. Those dust particles are about a tenth of the size of a human hair.
Those winds generally blow from east to west -- called the Easterlies or Trade Winds -- and they bring the dust about 3,000 miles across the Atlantic Ocean and into the Gulf of Mexico.
How much dust are we talking about?
NASA scientists said about 182 million tons of dust leave Africa every year, and that amount changes depending on the rainfall south of the Sahara.
The plume created by the dust is large enough that NASA can track the movement from space.
What’s the result?
Skies will generally look hazy or milky during days when the dust is particularly thick.
Sunsets will usually look much redder during a dust plume.
People who have certain types of breathing problems can experience issues. Allergy sufferers can also experience itchy, watery eyes and scratchy throats.
"It brings dust particulate, which, of course, is hard to breathe in,” said KPRC2 meteorologist Britta Merwin. “So, air quality goes down when it actually arrives."
Are there any benefits?
Merwin said the dust helps to keep tropical storm development in check.
“Having a little dust and dry air in the Atlantic – it’s in our favor,” Merwin said. “It keeps that hurricane development down.”
NASA scientists said that the dust also contains phosphorus, which is an element that is needed by plants but is limited in tropical regions of the Western Hemisphere.