All weather enthusiasts know the basic principles of precipitation, super-cooled water droplets, and condensation nuclei [CCN] from pollutants and natural aerosols. But in turns out the primary source of condensation nuclei up at Noctilucent Cloud height are thought to be some of the 100 tons of Micrometeorites and Cosmic Dust  that the Earth collects every day. It turns out that there is a lot of dust out there in space. Perhaps you have seen some space dust being produced if you have ever seen the dust tail from a Comet? NLC research is on going.

Still trying to see NLC? It turns out that it is rather tricky to actually see Noctilucent Clouds. The season is only 3 months from late May until mid August. You need clear skies which are often obscured by low maritime cloud in the remote upper Arctic. You must be far enough north, usually well above 50º, which rules out most of the world's population. NLC are only exceptionally visible from America or London and it is quite likely you will be in bed already on the day it occurs.  Northern Canadians, Scots, Scandinavians, Russians and Alaskans share an advantage. If you are too far north, you can't see them because it doesn't get dark. The sun needs to be well below the horizon which happens to be very late at night when most of us are asleep. If everything is working for you, then you still have to be in the right place at the right time with a display occurring. Aircrew have the advantage if you can get a twilight route on a great circle track between Europe and N. America in season.

Modern digital cameras can make NLC photography pretty easy. Hold the camera still and click in "Automatic" for starters. Other things to try include: turn your flash off, support camera still or use a tripod, manually focus to infinity, turn night mode on, activate noise reduction, compensate exposure +/- 1 or 2 as required, or use manual settings. You may be surprised to get a great picture, even possibly on a smart-phone or iPad!

Other interesting high altitude clouds are Nacreous Clouds, also known as Polar Stratospheric Clouds (PSC), which are 50,000 to 80,000 feet high. They are a rare stratospheric cloud which is known as the "Mother of Pearl" cloud because of the iridescent multi-color look that it has. They are most common at winter in the extreme far south over Antarctica where temperatures are coolest and only a handful of researchers can witness them. However, they can rarely appear in the high northern Arctic in winter often associated with a stratospheric wave which creates a further dip in temperature allowing them to form. Temperatures must be below -78º C. Opposite to NLC, these PSC clouds are a winter phenomena that increase with the lack of sunlight in the arctic and cooling during winter. In Spring, as the sun first emerges, very quickly a chemical reaction related to the evaporation of these clouds causes ozone depletion and creates the infamous Ozone Holes (Ozone Hole) that allow ultra violet radiation (UV) to the surface. Global warming at Earth's surface causes atmospheric expansion and cooling at high altitudes which should cause more PSCs in the future.

 Of interest, in the tropics, a completely unrelated but similar looking (and smaller) "Mother of Pearl" cloud may sometimes be witnessed when a giant thunderstorm manages to punch into the stratosphere. Occasionally, iridescent Pileus Cap Cloud [more] may be seen.

A normal cloud is made from the condensation of water vapour around a nucleus of some sort. There is no shortage of pollutants, dusts, volcanic aerosols, or pollens in the lower atmosphere and this occurs quite naturally. However, the Mesosphere is exceptionally clean and extremely dry making it absolutely impossible for traditional clouds to form. Some exceptions to the Day-to-Day rules needs to be understood and it includes Meteors, Rocket Exhaust, Explosive Volcanoes, and most likely Global Warming chemistry. Basically, for Noctilucent Clouds to form we first need to get Water Vapour and Condensation Nuclei up 50 miles above the Earth.

Volcanoes are a traditional source of both Water Vapour and Condensation Nuclei, making the super eruption of Krakatau in 1883 the suspected first cause of NLC. Much of the visible plume during an eruption consists of water vapor, like cloud, which will quickly evaporate back into the atmosphere. Likewise, most of the ash from the dense ash plume [Wiki] will fall nearby, but other smaller aerosols will remain aloft. These smaller particles may be suspended for thousands of miles, and others in the upper atmosphere will simply float around the world for many weeks or months! Essentially there are two main types of suspended volcanic material that will stay visible, fine "Tephra" Ash (small rock or glass particles) and Sulfur Dioxide SO2 gas which forms Sulfate Aerosols. The ash and ash-aerosols can be visible for many days looking similar to a thinning smog and stay suspended for weeks contributing to beautiful sunsets. They vary in size and fall quicker with weight, proportionate to size. The Sulfate Aerosols can also become visible and look similar to high thin Cirrus Clouds for many days, but their affects in the Stratosphere can persist for several years causing cooling of the Earth's climate. Both spread and dissipate rather gradually traveling as clouds in the wind, like a giant swarm.

Big eruptions are in the magnitude of one every couple of years. Astronauts filmed a spectacular eruption on 12 June 2009 from the International Space Station of Russia's Sarychev Peak [Must-see 6MB QuickTime] [NASA] [Wiki] [map]. This eruption punched well through the Tropopause into the Stratosphere where the particles traveled all around the world, quite possibly contributing to the unstable weather in the northern hemisphere 2010/11. One product of that eruption was a high Stratospheric bluish SO2 cloud that was visible everywhere in the mid-northern hemisphere shortly afterwards. Eventually the lower ash also spread out and formed a marked haze layer at the Tropopause everywhere in the northern hemisphere that could be easily seen on the Earth's limb in twilight. Weeks later, sunsets and sunrises were still showing an obviously exaggerated afterglow due to this upper ash layer, as in the photo to the left from Los Angeles, USA. The volcanoes near the Russian Kamchatka Peninsula and Alaska's Aleutian Islands are remarkably active. Historically they don't make the news because they are so remote, but as you can see, they still affect the rest of the world. Further away in the Philippians in 1991 Mt. Pinatubo [Wiki] had an even larger eruption which also caused beautiful sunsets in North America and Europe. Even more spectacular was the legendary 1883 eruption of Krakatau [Wiki] where global visual and climatic effects lasted several years. Remember that Noctilucent Clouds, discussed above, were first documented after Krakatau's extreme eruption. You may wish to also read about "1816 -the Year with out a Summer" [wiki] caused by 1815's Mount Tambora [wiki] eruption .