Friday, July 17, 2009

Noctilucent or Polar Mesospheric Clouds

Extremely rare noctilucent or polar mesospheric clouds were visible in the PNW Tuesday and Wednesday this week! These clouds are usually not visible south of 50 degrees north but recently have been seen as far south as Nebraska. These clouds form in the mesosphere about 50 miles above the earths surface in the Northern Hemisphere summer when the mesosphere is the coldest (yes that's right, coldest). The can only be seen after the sun has set (usually about an hour into twilight) when the sun is illuminating them from below (because they are so far above the earth's surface they still receive sunlight).

The first sighting of these clouds was in 1885 and there is no evidence to suggest they may have been around before then, so this is a relatively new atmospheric phenomena that is not well understood. Some believe that it is tied with global warming as they have become more are more frequent over time and have moved further south. Whatever the cause, they are beautiful and make for great photographs!

UPDATE 7/23/2009: More noctilucent clouds (NLC's) formed today that were even brighter! Click here to see them.

Noctilucent Clouds

Noctilucent Clouds

Noctilucent Clouds


Rick and Eileen said...

Those are beautiful. Thanks for the explanation. I almost understand it now.

Josh said...

Very Nice pictures....You have a gift...Very Nice