042219-wsj-news-weather-guys

There were widespread reports of dust residue on vehicles and tan/brown-colored snow earlier this month in parts of Wisconsin, Minnesota, Iowa and Nebraska -- the origins of which can be traced back hundreds of miles to Arizona, Texas and New Mexico.

Q: Why was there a reddish tint in the snow this month?

A: On April 11, there were widespread reports and photos of dust residue on vehicles and tan/brown-colored snow in parts of Wisconsin, Minnesota, Iowa and Nebraska.

The origins of these residues can be traced back hundreds of miles to Arizona, Texas and New Mexico.

On April 10, there were strong winds associated with an intensifying mid-latitude cyclone over Arizona and western Texas. Winds were gusting as high as 77 mph in New Mexico and 88 mph in Texas.

The winds associated with this storm generated large plumes of blowing dust in southeastern Arizona, southern New Mexico, northern Mexico and western Texas. Willcox Playa, a dry lake in southeastern Arizona, was the source of some of the dust ranging in shades of tan to light brown.

Satellite observations tracked the movement of this dust, or aerosol, northeastward across the Upper Midwest. As the wind weakened, it deposited the dust on the ground, often on recently fallen snow, where it left a reddish tint.

Dust can be transported across the globe. Micrometer-size soil particles from deserts can be lifted by the wind to high altitudes and transported over thousands of miles. Desert dust from the Sahara and Gobi deserts has been observed on the ice sheet of Greenland.

Ice cores in Greenland provide a history of the dust deposition as they appear as layers in the ice. The mineralogy of the dust in the ice allows scientists to trace the desert of origin. The source also allows scientists to determine global wind patterns from thousands of years ago, as atmospheric circulation patterns that carry Saharan dust will be different than the global circulations that can transport dust from Asia to Greenland.

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Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

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