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Dust From The Sahara | Earth Wise

July 9, 2020 By EarthWise Leave a Comment

A vast cloud of dust from the Sahara Desert blanketed the Caribbean in late June before drifting across the southeastern U.S. The phenomenon is nothing new; only the magnitude of the occurrence this time around was unusual. According to experts, this is the most significant Sahara dust event in 50 years.

The Sahara Desert is the major source on Earth of mineral dust, with some 60-200 million tons of it per year being lifted into the atmosphere. Convection currents over hot desert areas lift the dust to very high altitudes. From there, it can be transported worldwide by winds. The dust, combined with the extremely hot, dry air of the Sahara Desert often forms an atmospheric layer called the Saharan Air Layer, which can have significant effects on tropical weather by interfering with the development of hurricanes. The Saharan Air Layer typically moves across the North Atlantic every three to five days from late spring to early fall, peaking in the middle of the summer. It can occupy a layer as much as two miles thick in the atmosphere.

The dust plume this summer was highly visible from space, covering thousands of miles of the Atlantic Ocean and the Caribbean Sea.

A common effect of Sahara dust is that normally blue skies can acquire a milky haze, but beyond that can lead to spectacular sunsets. But apart from the visual spectacle, the dust can aggravate the conditions of people with asthma, respiratory illnesses, and allergies. On the positive side, as long as the dust is around, it is much less likely that tropical storms and hurricanes will form.

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Sahara dust blankets Caribbean, air quality hazardous

Photo, posted June 22, 2020, courtesy of Sagar Rana via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Fire-Driven Thunderstorms

March 6, 2019 By EarthWise Leave a Comment

In 2016 and 2017, wildfires in western Canada spawned thunderstorms that ignited additional fires, in some cases tens of miles away from the original fire. These fire-triggered thunderstorms are technically known as pyrocumulonimbus clouds, or “pyroCb’s”.

The physics of pyroCb’s is complex. When super-heated updrafts from an intense fire suck smoke, ash, burning materials, and water vapor high into the air, these elements cool and form so-called fire clouds that look and act like the cumulonimbus clouds associated with classic thunderstorms. What is different is that the heat and particulates in the smoke almost always arrest the ability of the cloud to produce rain. Instead, what remains is a lightning storm that moves across the landscape, triggering more fires.

These PyroCb events appear to be happening far more often, producing more energy, and erupting in places where they have never been seen before. As the world warms, wildfires themselves are becoming larger and hotter. In the past decade, wildfires have been burning more than twice as many acres as they did before the turn of the 21^st century. Along with the growth in wildfire activity, there has been an increase in PyroCb events, and there are now an average of 25 per year in western North America.

Apart from starting new fires, pyroCb’s also have similar effects as moderate-sized volcanic eruptions. Smoke and aerosols from wildfires can rise high into the stratosphere, where they can linger for months. Eventually, the particles carried aloft in the atmosphere do come down, dumping dangerous chemicals on far flung regions of the earth. But unlike volcanic eruptions, which are relatively rare events, pyroCb’s are happening more and more each year.

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Fire-Induced Storms: A New Danger from the Rise in Wildfires

Photo, posted July 31, 2013, courtesy of Loren Kerns via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

The High Cost Of The Cloud

May 2, 2018 By EarthWise Leave a Comment

More and more often we make use of “the cloud” – that mysterious place where we store, move, process and analyze data. We keep our photos there. We stream music and videos from there. We do our work there. Perhaps we have a mental image of all of this digital information floating above our heads in some ethereal way: like in a cloud.

The Chinese War On Pollution

April 10, 2018 By EarthWise Leave a Comment

For years, China has been struggling with some of the worst air pollution in the world. According to the European Union, only 1% of the country’s half a billion city dwellers were considered safe because almost all of its major cities were covered with what was described as a toxic grey cloud.