What Were Those Wild Looking Clouds in the Sky Today?? | Weather
So a lot of people have asked me what the crazy looking clouds that were looming around the skies of N Georgia earlier today. Some people even told me that they thought they saw a few flakes of snow!!! Well, there was no snow but what we saw in the skies today were what are called "Gravity Waves", so what exactly are these cool looking clouds? They are just that.... Waves!!
How Clouds Form
I always talk to school kids about how clouds form and I use the sponge example. As moist air rises it cools and condenses, basically colder air holds less moisture, so as the air rises the air "squeezes" the air like a sponge. Like a sponge that has moisture in it, the water becomes more apparent as the sponge is "squeezed" tighter. In other words as moist air rises, the air gets colder and squeezes the moisture enough to where clouds form.
So How Do Gravity Waves Form??
It happens in an atmosphere that is considered statically stable. This means that if you were to take a box of air and raise it up, the buoyancy would return it back to its original position. Take a pendulum and look at it from the side. Notice how when you take that ball and raise it up it will swing back and fourth until it returns to its equilibrium position. This is somewhat how the atmosphere works in an atmosphere that is statically stable.
When you have a day like today where moisture is returning from the Gulf of Mexico and hits the cold air that is in place across N Georgia, that moist air that is running into a stable atmosphere. Once that moisture gets lifted up, it condenses and turns into clouds. The air then goes downward like the pendulum, then back up, then back down... this goes over and over again in an attempt for the air to return to its origin. All of this is going on as the air is moving northward so you get a wave style motion, and in the end you get gravity waves!!
For The Hardcore Science Nerds, The Math!
The motion of the fluid particles can be described mathematically by the continuity equation, momentum equation and energy equation in Boussinesq fluid.
Where is the velocity vector, is the deviation from hydrostatic pressure, is the Boussinesq density, g is the acceleration of gravity, is a diffusion coefficient and is the kinematic viscosity.
By following the analysis used by Lombard and Riley , the equations of motion can be rotated into a coordinate system where the wave is periodic in only one direction, , which is aligned with the wave phase velocity.
So there you have it in a nutshell, gravity waves 101!
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