Mix of smoke and dust create a spectacular sight
Published 12:01 am, Monday, April 25, 2011
Ten days ago, a murky blanket of Mexican smoke covered much of Texas and painted the sky a milky gray.
On April 15, a dry cold front pushed the smoke over the Gulf of Mexico and replaced it with a thin veil of dust all the way from China. By midday, almost all of Texas was covered by the stuff.
Dust and smoke events like these occur almost every spring in Texas, and many other states also experience them. The Mexican smoke event described here reached the Great Lakes, and the Asian dust swept across the country and reached the Atlantic.
But something very different and quite spectacular happened the evening of April 15. When I went outdoors to make the usual twilight photo, I was surprised to see giant gray billows and waves wrapped around the entire horizon.
Many times I've seen and photographed smoke and dust plumes. Besides many Texas plumes, NASA twice sent me to measure smoke in Brazil and at seven major forest fires out west. So while I thought I had seen every possible plume or cloud of smoke and dust, the sky that evening presented the most unusual such display I've ever seen.
Since the front had chased the smoke away, I initially assumed the twisting plumes and lenses across the sky were Asian dust. But how could the relatively modest amount of dust form such dramatic displays?
Thomas Gill, an associate professor with the Department of Geological Sciences at the University of Texas at El Paso, is a prominent expert on blowing dust. I contacted Gill, who responded with a detailed account of what caused the eerie phenomenon I saw that evening.
"The weather data," he wrote, "showed winds gusting above 60 mph in some parts of the Texas and Oklahoma panhandles and southwest Kansas for about seven hours straight. Such strong winds over such a large area on the back side of the strong seasonal cyclone certainly raised a lot of dust and created conditions for even a little fire over the Big Country of West-Central Texas to explode into a huge inferno. ... I can't remember ever seeing so much smoke spread out so fast over Texas."
Gill sent several satellite images that showed dust and smoke being sprayed across Texas by the powerful wind storm. He explained that the strange display I saw in the sky was probably composed mainly of smoke laced with some dust.
I posted a video of the smoke formations at www.youtube.com/fmims. Hopefully there will be no more of these, but the ongoing drought suggests the possibility of more major wildfires.