The Boundary Layer is Cool!

August 27, 2008 at 11:36 am

It’s fall and back-to-school time! Due to the completion of my master’s thesis last winter, and teaching at Colorado College last spring, I haven’t actually taken any classes in over a year. And it’s been about two years since I took a class for … (dun-dun-dun) … a grade!

Image from Nasa Visible Earth

So, this fall, I’m taking a class called The Atmospheric Boundary Layer, where we’ll spend 16 weeks learning about that thin layer of air that lays between the surface and the rest of the sky above us.

I have had one day of class, and so far, I’m really excited about this class. I’ve known the basics of boundary layer (BL) dynamics for a while, but it will be nice to get an in-depth view. This is a part of the atmosphere that is full of turbulence. It is the part where dust and pollution is swept up, or trapped down inside. It is a place where all of the rules that we’ve learned about planetary flows (geostrophy, rossby numbers, two-dimensional kinetic energy dissipation, etc) don’t necessarily apply, or apply differently. It is the place where all weather essentially comes from, and the thin layer of air that we, as humans, experience daily.

Image from Nasa Visible Earth

On the first day of classes, the prof got us all jazzed up by looking at a series of pictures showing the importance of boundary layer processes, and in the course of this, he quickly explained something that has been beautiful and mysterious to me about the sky. When I fly, I often see clouds forming in the early afternoon. They almost always seem to form on a kind of grid, with long rows of clouds stretching out to the horizon like those in the pictures here. These are, I now know, called cloud streets, and they are formed when three dimensional convection (think warm moist air rising, forming a cloud, and cooler dry air sinking around it) is organized by the large-scale wind above the BL. So, effectively, you are seeing that thin line where the air which is mixed up by the surface is meeting the smooth flowing air above it. And the clouds all line up.

So, getting back to classes is fun. Learning is something I will never stop loving. And the sky is a beautiful and amazing thing.

Storms Passing