Pics and video above of the undulatus clouds as seen at Memphis International Airport. All were taken by MWN meteorologist Erik Proseus. |
Think of it in this manner – if a pond is undisturbed by wind, animals, bugs, or any other external force, it is perfectly flat (stable). Drop a pebble in the pond and ripples move out from the point where the pebble was dropped in. The water rises and falls creating miniature waves. It doesn’t keep rising; it doesn’t keep falling. The waves move out from the center and try to regain equilibrium, or stability, which is the flat and still pond. In the atmosphere, rising air reaches a stable point, gets forced back down once it rises above that stable point, then starts rising again, over and over as it attempts to regain equilibrium.
The atmospheric cross-section (or profile) from 3pm this afternoon is shown below. The red line is temperature, the green line is dewpoint (or moisture), the ground is at the bottom of the picture, and as you go up in the image, you are going up into the atmosphere. Wind is shown on the far right. This cross-section shows a stable layer (or inversion base) at about 3,000′. It also happens to be where the red and green line meet, representing 100% humidity and the presence of clouds. In today’s case, the upper level disturbance or gravity waves moving through triggered rising air, which got to about 3,000 feet, reached the stable layer, and then rose and fell around that inversion base or stable layer – thus “ripples” or waves in the atmosphere. We wouldn’t have “seen” those ripples except that that level was also where the moisture existed (the clouds). The stable layer separates wind above it that was blowing from the west and wind below it that was blowing from the north to northeast.
Atmospheric sounding from the NAM forecast model for 3pm CST. Details described in text above. |
Here’s one more interesting piece of evidence regarding the waves. Check out the radar loop below during the same time frame. There are a series of bands of light rain moving from west to east and oriented northeast to southwest. This could very well be the “triggering mechanism,” i.e., the upper-level trough or gravity waves, reflected in some bands of light precipitation near the surface. A very interesting weather phenomena today no doubt!
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