The Earth Story

Noctilucent Cloud Season Begins for Northern Hemisphere Noctilucent clouds (NLC) are the highest cloud formations on our planet. In this photo from the International Space Station, they are the blue wispy layers seen at the top of the atmosphere. They mostly form at latitudes of 50° or higher, with the majority found in polar regions during the summer. We've previously covered them (http://on.fb.me/1HHqVDj, http://on.fb.me/1RG4UvU), but we may know a little more about them now thanks to NASA’s Aeronomy of Ice in the Mesosphere (AIM) mission (http://on.fb.me/1FpEruW).

Original caption:

Night Dwellers

Never assume that what you can’t see isn’t there. Human beings by nature can only witness a fraction of what is out there, limited by our own biology and chemistry. Even the nearest stars (excluding our Sun) seem to disappear after sunrise but that doesn’t question their existence in whole now does it? At dusk, the stars reemerge, as they have done so for hundreds, thousands, millions, even billions of years, claiming their presence in the cosmos. And just as the stars have deemed themselves as night dwellers, at least from a human’s perspective, other bodies above us have also made reputations of shining at night; in this case, polar mesospheric clouds.

These clouds, also referred to as Noctilucent Clouds, exist approximately 80-85 km (≈50-53 miles) above the Earth’s surface near the coldest part of the atmosphere, the mesosphere. They become visible when tiny water particles (about 1/10,000 mm in diameter) in the upper atmosphere freeze into ice and reflect the sunlight. Polar Mesospheric clouds oftentimes appear in bluish hues because the stratospheric ozone layer absorbs most of the red light.

The formula for the development of these clouds in simple: low temperatures, water vapor, and a surface/nuclei for the water crystal to grow on. Once these criteria have been met, science takes over and with enough frozen water vapor and light the noctilucent clouds come to life. Next time you step outside and bear witness to these magnificent blankets that hover the horizon, thank the sun and the conditions of Earth’s upper atmosphere. Without either, the presence and existence of polar mesospheric clouds would be in question.

--Pete D

Photo Credit: NASA

References: 1. http://earthobservatory.nasa.gov/IOTD/view.php?id=7953 2. http://www.atoptics.co.uk/highsky/nlc2.htm

Earth’s atmosphere is an amazing thing, when you think about it. Without our atmosphere life would be unsustainable here on Earth; but what exactly is it?

The atmosphere is simply a layered mixture of gases, mainly nitrogen (78%), Oxygen (21%) and a mixture of argon, water vapour, carbon dioxide, methane and trace gases. These combined create not only the air we breathe, but also help serve as a sun screen, a temperature regulator and of course protect us from asteroid impacts (most of the time!).

The innermost layer of our atmosphere, and probably the most familiar to us, is the troposphere. Here and up until around 15km from the surface is where the majority of our planets weather systems reside and is where nearly 80% of the Earth’s air is located. The name “troposphere” comes from a Greek word that refers to mixing and this is exactly what happens within the troposphere, as warm air rises to form clouds, rain falls, and winds stir the lands below.

Past the troposphere we discover the stratosphere; a less dense region of the atmosphere which extends out to around 50km. Here, the oxygen molecules are transformed into ozone which forms a protective layer against harmful ultraviolet light from the sun- the importance of this layer has been made evident in our lifetimes; without which, skin cancer rates would be undoubtedly higher. Seeing as ultraviolet energy is being absorbed in this region, the stratosphere has quite extravagant differentials in temperature. At the base of the stratosphere it is extremely cold, around -80 degrees Celsius, at its top, the temperature rises to nearly 0 degrees Celsius.

After the stratosphere comes the mesosphere and here is where a lot of action happens. Any meteors which enter our atmosphere tend to be destroyed in the mesosphere; they “burn up” and never reach the Earth’s surface. This layer, which extends to 85 kilometres from the surface, is one of the fundamental reasons why Earth isn’t covered in meteor craters- if the moon had a mesosphere it would be a much smoother surface.

Next comes the ionosphere- named for the ions created within this layer from energetic particles of sunlight and space. The ionosphere allows for the transmission of radio signals which are invaluable, particularly before the days of satellite communication. Here is also were the auroras are created and who doesn’t love them, eh? The International Space Station has also made its home in the ionosphere.

Lastly, we have the exosphere. This tenuous portion of the Earth's atmosphere extends outward until it interacts with the solar wind. Solar storms compress the exosphere. When the Sun is tranquil, the layer can extend further outward. The reach of this layer varies between 1,000 and 10,000 kilometres, where it merges with interplanetary space.

Together, all these layers make our atmosphere which, sadly, is continually menaced by human activity. Between rising carbon dioxide levels and air pollution, ozone destruction and acid rain, we have divorced our relationship with our environment. It is important not to forget the delicacy which is life here on Earth, we should aim to maintain a mutually beneficial relationship with what has supported our time here on this lovely blue planet. After all, if the relationship is irreconcilable, the environment will get the house... !

-Jean http://wonderful-earth-story.tumblr.com

Some further information and reading for you:

http://www.ucar.edu/learn/1_1_1.htm

http://www.atmos.illinois.edu/earths_atmosphere/earth_atmosphere.html

Photo was taken from the ISS (credit: NASA/SPL)

These rare, mystifying clouds are referred to as “night-shining” clouds, or noctilucent clouds. They are formed under very restrictive conditions and are only seen in the summer, at latitudes north of 50 degrees.They originate in the layer called the mesosphere; making them the highest cloud formations in our atmosphere.

Normally, they are far too faint to be seen, but they can be visible when illuminated by sunlight below the horizon. As with normal clouds, ice crystals within noctilucent cloud systems need two things to grow; water and something for the water to adhere to, usually dust. While ordinary tropospheric clouds get their source of dust from things like desert storms, this is not a viable medium in the mesosphere where this dust simply cannot reach. Accordingly, it is speculated that these cloud formations utilise dust particles from outer space.

As for the source of the water vapor necessary to produce clouds at such extreme altitudes, upward winds during the summertime are capable of carrying water droplets from the moist lower atmosphere toward the mesosphere. That's why noctilucent clouds only appear during the warm summer months.

-Jean

For more information see: http://science.nasa.gov/science-news/science-at-nasa/2003/19feb_nlc/

Picture courtesy of Science Photo Library.

Night-shining clouds

Clouds that form high in the atmosphere may still glow, even when the sun has set from that part of the globe. Such clouds, known as noctilucent or polar mesospheric form about 76 to 85 kilometers(47 to 53 miles) above the Earth’s surface. They have been spotted from various points of view, including airplanes and spacecraft.

Low temperatures at those heights(-130 degrees Celsius,-200 degrees Fahrenheit), will freeze any water into ice crystals. Those crystals can then be illuminated by the sun, which has set from the point of view of people on the ground but can still illuminate the clouds high up. However, they can mostly be seen in far latitudes (above 50 degrees).

These clouds are sensitive to the amount of water in the atmosphere as well as temperatures in the mesosphere. They may also be getting brighter due to climate change.

The orange band seen is the stratosphere. Below that is the troposphere, the atmospheric layer in which most of the Earth weather occurs.

-CHD

Source: http://www.space.com/19381-night-shining-clouds-image.html Image: An photograph of night-shining clouds taken with a Nikon D3S digital camera using a 400 millimeter lens by an astronaut aboard the ISS on January 5, 2013. CREDIT: NASA Earth Observatory