Noctilucent clouds, also known as "night-shining" clouds, form on the edge of space about 50 miles high off the surface. They're made of ice crystals, which reflect sunlight to give off the clouds' signature blueish glow, according to NASA.
They're mainly seen in the summer just after sunset and before sunrise. Greg Johnson with SkunkbayWeather.com caught a display over Hansville, Wash. last summer with his nighttime time lapse video camera:
The clouds are usually spotted about 30-60 minutes after sunset when the sun is between 6 and 16 degrees below the horizon, according to SpaceWeather.com. That's because the clouds are so high they can still "see" the sun from that altitude but it's dark enough on the surface to spot their cool, blue glow. Typically these clouds are brightest in late June and July.
Scientists had thought the clouds were actually the result of "meteor smoke" and it turns out, the satellite data confirmed they're on the right track.
"The accepted theory was that the ice formed around meteoric smoke — very small, nanometer-scale particles that are remnants of meteors burning up in the atmosphere," said Diego Janches, project scientist for the AIM mission at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "With AIM, we were able to study the presence and variability of that smoke."
The satellite's data have led to more than 200 papers on Earth's upper atmosphere. Some of the key discoveries over the past 10 years include contradicting earlier assumptions that the noctilucent clouds were tied to the sun's 11-year cycle and would rise and fall with sun activity. But not so -- the satellite shows the clouds have been steadily increasing over the past decade, NASA says. They're not exactly sure why, but scientists now suspect it has to do with increasing greenhouse gases.
Comment: Captain Obvious chimes in: maybe because there's more "meteor smoke"?!
"Combining AIM's data with 36 years of measurements from satellite instruments showed a correlation between more frequent noctilucent clouds and increases in water vapor, a greenhouse gas, and decreasing upper-atmosphere temperatures — a side effect of warming near the surface," wrote Sarah Frazier with NASA's Goddard Space Flight Center.
They've also been given more data to study how heat moves in the upper atmosphere, finding it's more linked to atmospheric circulation than direct heating form the sun, Frazier said. And they've also found the noctilucent clouds are likely responsible for what had been mysterious radar echoes picked up during the summer.
Next up for the satellite is to study gravity waves -- which are oscillations in the air usually caused by weather and winds near Earth's surface.
"These gravity waves affect the entire circulation of the middle and upper atmosphere," said Cora Randall, principal investigator of AIM's Cloud Imaging and Particle Size, or CIPS, experiment at University of Colorado Boulder. "These are really important for the global atmospheric structure and composition, and even affect the polar vortex."
Reader Comments
aim.hampton.edu/library/index.html
By looking up some papers, it become quite obvious that there is no "more meteor smoke", but instead a rise in methan, CO2 and water vapor is to blame (connected through different mechanisms). 10 years of observations didn't produced the slightest hint of an increasing accumulation of meteor dust in the upper atmosphere.
So maybe the editor want to change his name into "Captian to lazy to read".
[Link]
About the increase in asteroids activity and the subsequent increase in atmospheric cometary dust (based on NASA data):
SOTT Focus:NASA space data supports citizens' observations: Meteor fireballs are increasing dramatically
SOTT.net last looked in detail at the frequency of meteor fireballs in 2013, using the data garnered by the American Meteor Society (AMS). SOTT.net pointed out the increasing frequency of...That was my point, nothing else. Fact: no increase in cosmic dust.
And since you brought up fireballs. I think I understand what happed. The conclusion seems to be: More fireballs = more dust = more noctilucent clouds right? Well, there is a problem since there is no such thing as "more dust", the conclusion must have a flaw. And indeed, there is a flaw. Actually, within the article you linked to at the end, there are many flaws. Let me quote: If the suggested increase is indeed real, it should generating a lot of attention, but first and foremost within astronomical circles. And, without a doubt, it would. It would spike a lot of discussions long before the media jumps in an turn it into sensationalism. But surprisingly (or not), there is a suspicious silence on that particualr topic. Why? One can be sure that all the numbers presented in the articles are already known within the scientific field and yet, no one seems to care.
Well, the answer is simple. There is no increase in fireballs in the way the SOTT article suggest. How can I know this? OK, first the article compares single years like 2013 to 2015. Thats a rediculus short period and in itself has no statistically significant weight. Second, the seemingly long-term increase from 1995 to 2015 lacks important factors like the change in the amount of observatories in that period, the change (or the lack of) the threshold of what is recorded and what can be recorded due to the development of newer and more sensitive technology and last but not least, the human factor: [Link]
But interested readers are not that helpless because there is a source that provides data from which a solid conclusion can be derived: [Link]
There you have the visual meteor database which is, ironically, the first source NASA recommeds if one is interested in meteor counts. There you have all the factors in one graph you need to deduce the real (unknown) number of asteroids comming in each year. Not only are those numbers vastly greater than those from the AMS, but you can also see how big the variations are from one year compared to another one.
The graph shows perfectly that over time, the correlation between observers, the observing time and the amount of meteors observed is in line. If an actual increase would be real, we would see that despite the two other factors still in correlation, the number of observed meteors starting to deviate from the line. But no such thing can be seen in 38 years of observation.
So whats the conclusion? No increase in cosmic dust indicate no increase in meteorite activity and the data show exactly that. So, no mystery here, just flawed reasoning on a insufficent basis. Sadly, thats whats most blogs do today. And by the way, there you have the reason why no one with a sufficient scientific backgroud and profession in the field talks about it: Because its not real.