Clouds

It is interesting being a professor in a department in which you only understand a little bit of the science.  I am really an expert in upper atmospheric physics, but sometimes you are expected to know more.  For example, a couple of years ago, I was asked to teach a class on weather.  Well, to be honest, I didn’t know anything about the weather.  Why was I asked to teach that particular subject?  The professor who normally teaches it went on sabbatical, and was “willing”.

There are a lot of interesting things about the weather that I never knew about.  I didn’t really understand fronts.  I know what cyclogenesis means now.  How many people on Earth can claim that?  Hopefully every student who graduates from this department!  One thing that I did learn, that I am semi-proud of is how clouds form.  When I said this to a room full of atmospheric scientists, every single one of them asked me, seriously, “How?”  This is an active area of research, and there are many mysteries about how clouds actually start to form and the process of the first droplets and such.  I have no idea how clouds REALLY form, but I know the general idea.

You see, warm moist air rises.  As it rises, it cools.  At some point, it becomes cold enough that the air can no longer hold the water vapor and droplets start to form.  That is the simple story that I can understand.  I can explain this to my kids (I have!)  Complicated stuff, like real cloud formation is, well, complicated.

Why am I writing this?  Today, on a balloon launch, we saw some pretty amazing clouds.  They are rare and are called mammatus clouds.  The students sort of freaked out at them, since they were so weird.  Here is a picture.

Most clouds are flat bottomed, since the temperature is pretty uniform horizontally.  So, warm moist air hits the temperature in which the water starts to condense (the Dew Point!) at the same altitude.  These are somewhat strange because the bottoms are not flat – they are very bumpy.  This is due to little cells of convection cause the air to go up and down, which gives the clouds the rolling hills appearance.   Very cool clouds!

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About aaronridley

Professor at the University of Michigan, Department of Climate and Space Science and Engineering.
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