Upper-Level Clouds

The series on clouds concludes with a discussion about upper-level clouds. These clouds are high enough up in the atmosphere that they are almost exclusively composed of ice crystals. Their composition allows them to take different shapes than their lower-in-the-atmosphere cousins. The most common type of cloud at this level is the cirrus cloud. In the first picture above, the wispy clouds that seem to be streaking away from the main body of the cloud are cirrus clouds. They have an almost fibrous look to them. The second picture contains both cirrus clouds and cirrocumulus clouds. Notice that even the cumulus clumps seem to lack the sense of substance that the cumulus and altocumulus clouds had. Finally, the last type of upper-level cloud is a type of cloud unique to our modern area. The third picture shows several straight clouds that look like paths in the sky. These clouds are contrails (from the combination of condensation trail) and form as the result of air cooling as it passes over the wings of an airplane. These contrails may last for just a few minutes or persist for several hours, depending on the conditions in the region where they form. While it may seem surprising, it appears that these contrails have an effect on the weather. A study done of temperatures reported on the day of the September 11 attacks (when all planes were grounded and no contrails formed), found that the average temperature was warmer than it was on September 10 or September 12 and that this increase was not the result of other phenomena.
This is probably the end of the series on clouds. It's been a pleasure to share a few of my cloud pictures with you, and I hope you've enjoyed this little primer on clouds.