Noctilucent Cloud Season is Here

Noctilucent Clouds from the International Space Station

Good news for people who love their unusual atmospheric phenomenon!  There's a strange type of cloud that you can only see during the summer in the higher latitudes.  All of the clouds that we usually see form in the troposphere, which is the lowest and thickest part of the atmosphere.  Noctilucent clouds can only be found in the mesosphere, 50 miles above the Earth's surface.  Their existence is still a bit of a mystery, as clouds need both water vapor and an aerosol, like dust, to form, and it's basically impossible for airborne dust to get that high into the atmosphere.  Scientists think that the aerosol is debris from space.  The Earth gets bombarded with a lot of space junk every day, and quite a bit of it gets stuck in the upper atmosphere.  The water vapor is no mystery, upwellings of moist air are strong enough during the summer months for the water to get into the upper atmosphere, which is why you can only see these clouds during the summer.

Now, historically, southern Pennsylvania is too far south to see these clouds, as they stayed in polar and subpolar latitudes.  But global warming has brought them farther south.  In an interesting twist, global warming, while warming the lower atmosphere, actually makes the upper atmosphere colder, widening the range for noctilucent clouds to form.  Noctilucent clouds have been spotted as far south as Virginia and Colorado.  So, it may be unlikely, but it is possible.  Of course, your best odds to see these clouds are to go north.  I would love to see them, they look really cool.

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