Atmospheric waves on camera!

| October 4, 2007 @ 9:28 am | 6 Replies

At UAH, I do a lot of research on atmospheric gravity waves, and how they affect tornadoes, and our weather in general. Some very interesting waves occurred yesterday near Des Moines, Iowa, captured brilliantly on Doppler radar and on 3 webcams, similar to the SkyCam network here. Daryl Herzmann, of the Iowa Environmental Mesonet, made me aware of this case yesterday.

We are familiar with waves moving along the top of a fluid, such as a river or the ocean. These waves can be caused by boats, etc. Water is heavier than air, and when it is lifted up above equilibrium, gravity brings it back. This sets up “gravity waves”. In the atmosphere, when the air is stable (resistant to vertical motion), and it gets displaced from its equilibrium, gravity waves are initiated in the air, too. They are typically hard to see, unless they help form clouds or rain, or can be detected on radar. We’ll discuss these more later.

In the Iowa case, an area of thunderstorms was approaching from the west, but the air in east Iowa was very cold and stable near the surface (see model sounding below). When the storms disturbed this air, a special type of train of gravty waves called an undular bore was initiated. The dense, cold air near the ground acted almost like a shallow pond, and the storms disturbed it, like a person throwing a rock in a pond.


A train of 4 waves was set up. In waves, you may have noticed that the motion is back and forth as well as up and down. Radar picture from Des Moines, Iowa NEXRAD shows this…with green showing winds towards the radar, and red showing winds away from the radar, one can see the wave features moving SE, and the alternating winds from SE to NW!


Using software we often use in analyzing weather systems at UAH, we show a vertical cross section through the waves (looking at them from the side), where they also show up nicely. In the areas to the left of green, inbound velocities and to the right of red, outbound velocities, convergence and upward motion produces clouds.


If you watch the videos below (from Iowa Mesonet), you can see 3 or 4 dark cloud bands (due to the convergence and upward motion caused by the waves), with clearer areas between them, caused by downward motion due to the waves! Wow!


{vidavee id=”2687″ w=”320″ } Click here for movie.

You can also see the pressure (left) and the wind direction (right) oscillating back and forth very quickly at Des Moines, with high-resolution surface data below.



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