Tuesday, September 6, 2011

Why is it so smokey?

I have been getting lots of questions on fires this morning because of the extreme amount of smoke in the area. Many people are worried if there is a fire near them and after the past couple of days, who can blame them? East Texas awoke to a tremendous amount of smoke this morning even though there was not an increase in fires. So how did this happen?

As the sun sets in a cool air mass, the earth cools rapidly causing ground temperatures to be much cooler than temperatures just above the surface. This is known as a temperature inversion. Basically the near ground atmosphere separates from the remainder of the atmosphere. We call this atmospheric decoupling. This also allows for the surface winds to diminish greatly. With the temperature at the surface much cooler than the temperature 500 or so feet above the surface, the smoke becomes trapped in the lowest layer of the atmosphere. As the smoke rises, it hits the temperature inversion and can go no higher so it spreads out across the entire area.

When we look at the sounding data for Tyler, or the temperature profile, the red line shows the air temperature as you go up in the atmosphere. Notice at 7AM this morning there was a strong inversion were the temperature decreases rapidly in the lowest 500 feet of elevation. By noon you can see the inversion in the lowest 500 feet is now gone and this allows for the smoke to mix out. Now there is another temperature inversion around 6000 feet in the atmosphere so the smoke can’t completely clear out but at least it will be a little easier to breath. Depending on what happens with the fires today, we could see a repeat performance of the smoke tomorrow morning.

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