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    Image Courtesy of Dione Rossiter

From: Dione Rossiter
Iquique, Chile, November 3, 2008

Graph from October 22 Flight

I wanted to share with everyone a typical graph we sometimes use to understand clouds. I know it may look scary but I’ll walk you through what each line in the graph means.

The easiest line to start with is the red line. This line represents the altitude of the airplane (how high and how low the plane flew off the ground). As you follow the line to the right, you are following how the plane moved in the air with time. You can imagine a little airplane sitting on the red line following whatever it does. When the line goes down, the airplane has gone lower and when the line goes up, the airplane has gone higher. Sometimes the plane stays flat; this is called a flight ‘leg.’

We usually study clouds by doing legs within the cloud. Very often we fly legs in a ‘stair step’ fashion. Can you see where the red line looks like a set of stairs? This is when the airplane flies under the cloud, through the bottom of the cloud, in the middle of the cloud, and then we climb even higher to do a leg in the top of the cloud. Whenever there’s a spike in the blue line that means the plane flew through a cloud! The blue line represents liquid water (this of course a cloud!) measured by an instrument called the Gerber Probe.

Can you see that the first leg has no liquid water (the blue line stays low)? This is when we are under the cloud. As we climb higher and higher into the cloud (climb the steps with your finger), the blue line wiggles higher and higher up the graph. This means that there is more water at the top of the cloud than the bottom. This is one of our first steps in understanding a cloud!

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