I woke up at 3:30 am to a very bright sky that shone through the shadows. I got up to have a look and was surprised to find noctilucent clouds. I live in Bend Oregon and since I have lived here (18 years) I have seen this only twice more. Beautiful.
Noctilucent clouds tend to drop even further after the summer solstice, according to Tony Phillips of SpaceWeather.com. If you are at a north latitude, now is a good time to watch them!
What are noctilucent clouds? Noctilucent clouds form in the highest reaches of the atmosphere: the mesosphere - up to 50 miles (80 km) above the Earth's surface. They are believed to be made of ice crystals that form into fine particles of meteorite dust. They can only form when temperatures are incredibly low and when water is available to form ice crystals.
Why do these clouds, which require such cold temperatures, form in the summer? It is because of the dynamics of the atmosphere. Actually, the coldest temperatures of the year approach the poles in summer at that height of the mesosphere.
Here's how it works: During the summer, the air near the ground heats up and rises. As atmospheric pressure decreases with altitude, rising air expands. When the air expands, it also cools. This, along with other processes in the upper atmosphere, drives the air even more and makes it cool even more. As a result, temperatures in the mesosphere can drop as low as -210 degrees Fahrenheit (-134 degrees Celsius).
In the northern hemisphere, the mesosphere often reaches these temperatures in mid-May, in most years.
Since clouds are so sensitive to atmospheric temperatures, they can act as a proxy for information on the wind circulation that causes these temperatures. First, they can tell scientists that circulation exists, and also tell us something about the strength of circulation.
How can I see the noctilucent clouds? If you want to see the clouds, what steps should you follow? Remember you have to be at a relatively high latitude on Earth to see them - typically between about 45 degrees and 60 degrees north or south latitude, although clouds can sometimes be seen at lower latitudes, particularly after the solstices.
For best results, look for these clouds from May to August in the Northern Hemisphere and from November to February in the Southern Hemisphere.
Noctilucent clouds are mainly visible when the sun is just below the horizon, for example, from about 90 minutes to about two hours after sunset or before sunrise. At such times, when the sun is below the Earth's horizon but is visible from the high altitude of the noctilucent clouds, sunlight illuminates these clouds and makes them shine in the dark night sky.
Scientists studying these clouds have included those from NASA's Aeronomy of Ice in the Mesosphere (AIM) satellite. This satellite, launched in 2007, has observed noctilucent clouds using various instruments on board to collect information such as temperature, atmospheric gases, the size of ice crystals and changes in clouds, as well as the amount of meteoric space dust that enters the atmosphere. You can find out what they are learning on NASA's AIM page.
Bottom line: Noctilucent or bright clouds are seen at night during summer in Earth's high latitude regions. They form in the highest reaches of the atmosphere: the mesosphere - up to 50 miles (80 km) above the surface.
Visit SpaceWeather's real-time night cloud gallery
Visit the Facebook page Noctilucent clouds around the world