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What's with this smoke? A science look at WHY it's in Wilmington...
Submitted by Tim Buckley on Fri, 03/25/2011 - 8:24am.
An unsettling way to start the morning, with the smell of smoke hanging heavy across the Port City. Thankfully, it's coming from the Onslow County fire in Camp LeJeune, but considering the strength of the smell you'd swear the fire were right around the corner. So how can the smoke travel nearly 40 miles and be so dense so far away? I wanted to spend some time explaining this and what exactly goes on in the atmosphere to make this happen.
It all has to do with how the Earth is heated, and how it releases that heat back into the atmosphere. We'll start off with the basics.
As we all know, the sun is the heat source for the Earth. During the day, the sun's rays enter the atmosphere and heat the Earth's surface. This heat is absorbed by the ground. Makes sense right? As the ground is absorbing heat from the sun, it is also releasing heat into the atmosphere above it - heating the air. So it's really the GROUND heats the air around us, NOT the sun. This is why it gets cooler as you go up in the atmosphere farther away from the ground, which is the heat source. This continues throughout the course of the day.
When the sun sets, things begin to change. Of course, we lose our heat source at nighttime, which is why it gets cooler. But on clear nights - it's important to look at just how at atmosphere gets cooler. At nighttime, the ground continues to release all of the heat it absorbed from the sun during the day. As it releases the heat - it is cooling down, very quickly. In fact, if there aren't any clouds to absorb this heat as it's being released, the ground is cooling down faster than the air above it. So often times the surface will actually be cooler than the air just above the surface. This is what us meteorologists call a temperature inversion - since it's opposite of what we typically expect.
We know that cold air sinks, and warm air rises. So since the surface is actually colder than the air above it, it can't rise through the atmosphere. In short - it "traps" itself close to the surface. This also means that everything that's released into the air while this night-time inversion is in place, will stay there because there's nowhere for it to go! So, if you have a huge wildfire going on at the surface, this smoke cannot escape high in the sky - instead, it's going to remain trapped in the lower levels, close to us on the ground.
Now that we have all this smoke from a huge fire collecting over our heads throughout the night, all we need is some wind to carry it far away. With winds out of the northeast around 10 mph, some simply math will tell us it only takes a few hours for all that smoke to make the trip down US 17 from Onslow County down to Wilmington itself. That's exactly what happened. Before you know it, the fire smells like it's just outside your door.
So how do we get rid of the smoke? Well, thankfully the sun should take care of that rather quickly.
Once the sun returns and heats the ground, the surface will again become warmer and the process will start over again. This warm air will begin to rise and create upward currents through the atmosphere. Since there's some upward motion again, the smoke is no longer "trapped" and can finally move up instead of spreading out across the area. So - we should see at least a dramatic reduction in smoke this afternoon as our circulation re-establishes itself.
In case you were wondering, that foul smell you sometimes find on clear, cold mornings across the Port City? That's the Riegelwood paper mill fumes getting trapped in the lower levels and causing us to cover our nose as far as 20 miles away.
The good news in all of this is that it looks like our friends in Onslow County will get through this fire without losing any structures and with no injuries. I think we can all use a little bit of that rain headed our way!
Have a great weekend!
By: Tim Buckley