This week let's take a look at a weather phenomena that has been in the news in the Southwest: dust storms.
On July 5, 2011 a huge dust storm hit Phoenix. It was a wall of rapidly blowing dust 5,000 feet high in some places.
This time-lapse video shows how it looked as the curtain of dust approached.
Dust storms occur most frequently in arid regions, such as the southwestern United States, the dry areas of Australia, the Middle East (see a similar dust storm that happened in April in Kuwait), China and the Sahara Desert. Here in Arizona we have them most frequently in the summer, typically in late June and July, although sometimes into September if the summer rains fail to materialize.
Why summer? The dust storms are fueled by the intense heat that causes air to rise, just like happens with thunderstorms. The rising updrafts eventually begin to cool when the air gets high enough and a rush of air starts down. Under certain conditions, the thunderstorms collapse and the down rushing air can be intense. Huge gusts of wind pick up any loose soil particles as they flow by. Where there are large areas of exposed soil -such as in deserts- the amounts of dust picked up can be extremely high.
To give you an idea what dust in the air was like during the recent storm, let's take a look at the records from the weather stations that record the amount of particulates in the air. On a normal day, the average amount of particulates is 38 micrograms per cubic meter of air. On July 5th the readings ranged from 2,576 to 5,190 micrograms of particulate per cubic meter. (Source: The Arizona Republic, July 24, 2011). That's a lot of dust!
For some related hands-on activities, try the Wind Power post.