- In recent days, rare noctilucent clouds have been visible in the northern USA.
- These clouds form in the mesosphere, almost 80 kilometers above the ground.
- Noctilucent clouds are best seen at dawn and dawn when the sun is 6 to 1
- The "season" For viewing noctilucent clouds from the beginning of June to the end of July.
Noctilucent clouds, the highest clouds on earth, have been visible in parts of the north of the United States in recent days.
The word sounds almost from space, and in fact, noctilucent clouds differ from their better-known earthly relatives.
If you have never heard of noctilucent clouds, it is because they occur under severe atmospheric conditions and are only visible for a few weeks each year, and what happens to be there.
Above is a photo showing an example of noctilucent clouds from Roseburg, Oregon, on Sunday night. They have also been seen in several other places in recent days, including Nevada Minnesota and across the Atlantic in United Kingdom .
Noctilucent clouds were first seen in 1885 after the Indonesian volcano Krakatoa erupted and clouds of volcanic ash flung miles into the earth's atmosphere said Gary Thomas, a professor at the University of Colorado, to NASA.
While they might look like cirrus clouds, noctilucent clouds are forming differently than the more common, icy, cloudy clouds. For example, noctilucent clouds develop in a different area of the atmosphere than cirrus, cumulus and even storm clouds (cumulonimbus clouds).
In addition, cirrus clouds are often seen during the daytime, while noctilucent clouds occur only in summer and are best viewed at dusk, after the sun has dropped below the horizon in the evening or rises above the horizon in the morning.
The image below shows the layers of the Earth's atmosphere. Most of our weather occurs in the lowest layer, the so-called troposphere, which extends from the surface of the earth to a height of 12 miles into the sky.
Cirrus clouds form in the highest parts of the troposphere, where temperatures can fall to about minus 22 degrees Fahrenheit. At this temperature, sufficient water vapor is available in the atmosphere to assist in the development of ice crystals that produce cirrus clouds.
In contrast, noctilucent clouds form in the mesosphere almost 80 kilometers above the earth's surface. At this altitude in the atmosphere, so few air molecules exist that it is extremely difficult to produce ice crystals. The temperature must fall below minus 207 degrees Fahrenheit to form ice crystals, and there is so little water vapor that the air in the mesosphere is a thousand times drier than air from the middle of the Sahara .
Despite the harsh conditions Under these conditions, tiny cubic ice crystals form north of 40 degrees latitude in the summer mesosphere. In the United States, these include Washington, Oregon, Idaho, Montana, Wyoming, North Dakota, South Dakota, Nebraska, Minnesota, Iowa, Wisconsin, Northern Illinois, Michigan, Northern Indiana, Northern Ohio, Pennsylvania north of the Pennsylvania Turnpike, North New Jersey, New York and New England.
The "season" for viewing noctilucent clouds in the northern hemisphere begins in early June and, according to meteorwatch.org, lasts until the end of July . While they are present in daylight, the best time to look at noctilucent clouds is at dusk.
"Look west, maybe 30 minutes to an hour after sunset, when the sun has dropped 6 to 16 degrees below the horizon ," Thomas said, according to NASA. "If you see bright blue and white tendrils in the sky, you've probably spotted a noctilucent cloud."