A huge plume of dust from the Sahara Desert in North Africa has passed through the atmosphere, thousands of feet above the tropical Atlantic Ocean, and now blankets the Caribbean and nears the southeastern United States .

Although summer dust plumes are a common occurrence, it appears to be one of the most extreme in recent memory. It is so tall that it has been nicknamed the Gorilla Dust Cloud.

“It is the most important event of the last 50 years. Conditions are dangerous in many Caribbean islands,” Pablo Méndez Lázaro, of the School of Public Health at the University of Porto Rico.

NASA’s latest model to project the dust path brings it into the deep south of the Gulf of Mexico on Wednesday. The next round will hit Texas Thursday through Saturday, then roll back east over the Southeast and Tennessee Valley region.

On satellite images of space, the dust usually appears somewhat subtle and faint, but this plume can be seen as clear as daylight. The photo below was taken on Sunday from the International Space Station. “We flew over this plume of Saharan dust today in the mid-western Atlantic. It’s incredible the area it covers!” astronaut Doug Hurley tweeted.

These Saharan dust plumes, called Saharan Air Layer (SAL) by meteorologists, are lifted by strong windstorms crossing the Sahara Desert. Dust enters the Atlantic Ocean near the Cape Verde Islands, inside the intertropical convergence zone where tropical systems often flourish.

NOAA’s GOES satellite captured this series of moving images on Friday as dust entered the deep tropical Atlantic from Africa.

The dust moves along the trade winds, a belt of winds moving east to west near the equator that establish themselves firmly during the summer. The dust layer can range from a few thousand feet above the surface to 20,000 feet high.

While the dust masses generally remain intact for most of the transatlantic voyage, they generally become diffuse and diluted by the time they reach the Caribbean. However, so far this particular layer of dust defies the odds.

Here is a series of before and after photos taken on Sunday on Caribbean islands like Antigua, St. Barts, Puerto Rico and Trindad and Tabago:

When the dust is thick, it results in a very hazy yellow-brown sky. But when the dust is on the low side, refraction and reflection of light can contribute to stunning sunrises and sunsets, which can help explain at least part of the Sunday sunset in Miami.

Health impact

The dust was so thick that the weather services in Barbados issued a ‘severe dust haze warning’ urging residents to take action due to the drastically reduced visibility and potential breathing problems for those with difficulty breathing .

NASA satellites measure the intensity of dust clouds with a metric called Aerosol Optical Thickness (AOT). This metric indicates the degree to which aerosols prevent the transmission of light into the atmosphere: 0.01 indicates a crystal clear sky, 0.4 indicates very hazy conditions, and a 4 means the pollution is so dense that the sun cannot cannot be seen in the middle of the day.

As of Tuesday, AOTs were about 1.5 – very dense – in the thickest mass of dust near the islands of Hispaniola and Jamaica, limiting visibility to less than a mile in parts of the Caribbean and making quality very unhealthy air as measured by the World Air Quality Index Project.

Research shows that airborne dust can have adverse health effects, one of the most important being lung disease. Inhalation of dust particles in the respiratory tract may trigger an inflammatory immune response. Dust is very unhealthy for people with pre-existing conditions such as COPD, asthma and allergies, but dust as thick as the plume heading to the United States can even be harmful to people otherwise. good health, if the exposure lasts too long.

Another complication posed by this impending dust cloud is its coincidence with COVID-19. A recent Harvard University study found that increased pollution, especially particles, like dust, can lead to increased hospitalizations and death rates from COVID-19. Health officials recommend wearing a mask to protect yourself from inhaling the dust.

COVID-19 cases have increased in Florida and Texas, which are in the path of the plume. As dust spreads to southeast and then to Texas, air quality indices should be in an unhealthy range.

Dust clouds, hurricanes and climate

Dust is most often known to be a hurricane killer. Anyone who has lived in Hurricane Alley can tell you that those dry, dusty layers dampen the humidity needed to power the hurricane’s engine. Typically, when thick layers of dust are present, tropical activity remains calm, and that is what is expected over the next week.

Surprisingly, much of the soil and nutrients in the soil, in places like South Florida and the Caribbean, are made up of African dust that has settled over millions of years. In South Florida in the summer, almost half of the airborne particles come from Africa. Studies show that the nutrients in African dust in subtropical and tropical soils can be essential for maintaining vegetation.

For the oceans, this can be both a blessing and a curse. Scientists believe nutrients transported from the Sahara Desert helped build and nourish Coral reefs in the Caribbean, Bahamas and Florida for millions of years. Without these minerals, they say, the area around the Bahamas is simply too poor in nutrients to support the vibrant reefs that exist.

On the other hand, during years of strong dust storms, coral seems to suffer or even die. One theory is that contaminants mixed with dust from agricultural practices in the Sahel region of Africa may contribute. In addition, too many minerals in the dust can cause hyperfertilization, contributing to the proliferation of algae harmful to the coral.

In addition, dust can also contribute to the warming of our atmosphere. In a study published in April, researchers found that scientific climate models currently underestimate the amount of coarse dust in our atmosphere by four times. This is because the models deposit dust from the atmosphere too quickly. Dust, they say, seems to have a definite influence on the warming of our atmosphere.

But for the more immediate future, the bigger concern is how ubiquitous dust cover will be in the tropical Atlantic this summer. With all signs indicating a very active hurricane season, a more persistent dust layer could help defend against tropical activity. However, once the dust begins to settle, it looks like there won’t be much to stand in the way of a busy hurricane season.