If you are one of the millions of people in the Midwest and Eastern United States who have recently gazed up at the sky, you may have noticed the sun shining through a strange milky haze. This extended haze was not caused by clouds, but rather by smoke from wildfires in the western United States.
The smoke floated in the middle levels of the atmosphere many thousands of feet above the ground. Although it was too tall to smell, it brought spectacularly toned sunsets from New York to Washington D.C. and Missouri.
Red sky at night
Lasting about a week from September 12 to September 19, the smoke could be seen in satellite images as light gray wisps and spots and was especially noticeable on the dark contrasting Atlantic water.
Soot particles are much larger than air molecules and are better able to disperse the yellow, orange and red wavelengths of sunlight. The intensified oranges, pinks, and reds during sunset occur when the sun’s rays have to travel through more smoke. This happens when the Sun is very low near the horizon rather than directly above, hence the fiery sunsets.
Riding the jet stream
The smoke on the east coast comes from the horribly large and persistent fires in the western states. Smoke from those fires is popping up not only off the east coast but also across the Atlantic to Europe.
How has all that smoke migrated so far? Blame it on the whims of the jet stream.
The jet stream is a belt of fast high-altitude winds that travels west to east around the hemisphere in mid-latitudes. The jet stream is always present, but the wind speed and exact trajectory in the world vary every day.
In early September, the jet stream’s path was steeply sloping south, cutting through the western states. When this happened, the air current picked up the rising plumes of smoke and carried them across the United States in a layer of air between 10,000 and 20,000 feet above sea level. As the smoke layer ran eastward at up to 100 mph, it spread through cities along the way, obscuring the sun and creating red sunsets.
A connected world
Smoke isn’t the only aerosol that can navigate the Earth with wind currents. Pollution from China regularly travels to the United States, where it has been detected along the east coast. The fine dust that rises from the Sahara Desert in Africa can be swept west to the southeast of the United States, as happened a few months ago.
After a week of foggy skies, a large mass of air from Canada blew towards the east coast bringing smoke-free air. But the western US fire season continues, and if the jet stream drops south again, the east could experience further blasts of smoke-laden air. The world may be vast, but the wind currents connect us all.