More Kelvin-Helmholz Waves

January 8, 2008 at 10:35 am

My good friend Dougie B gave me a call while I was sniffling on the couch this afternoon and told me to run my sick butt outside into the cold and check out the cool clouds in the southwestern sky.

K-H Wave Clouds

This was something I’ve never seen – wave clouds breaking in a clear blue sky. Usually there must be a whole lot of moisture around for something like this cloud to appear. There was some discussion as to whether these were originally triggered by a jet contrail or naturally occurring due to a layer of moisture in the air. Here is the sounding info from Denver this morning:

As you can see, there was a strong inversion over Denver this morning, way up at 400mb and some strong directional wind sheer associated with it, but that doesn’t make wave clouds break. What makes these clouds is the more subtle change lower down. Right around 600mb, there is an increase in relative humidity and a decrease in windspeed, but no change in wind direction. This little change can produce thin clouds. They break because the lower layer is moving slower than the upper layer, just like waves break on a beach as the lowest part of the water moves slower than the tops of the wave.