Noctilucent clouds and the Earth's interface with space

This story about noctilucent clouds on NASA’s Science website made me think about a few things.

 

What I wonder is this: could noctilucent clouds be a proxy for cosmic ray interactions? While there are a lot of high energy galactic cosmic rays (GCR’s), there are  GCR”s that are coming in at low energies as well. The lower the energy, the higher in the atmosphere would be their primary target area. The lower the energy, the more the earth’s magnetic field is deflecting them, redirecting then towards the magnetic poles like the protons of the solar wind (which have much lower energies).

Noctilucent clouds are not yet well understood, and given the size of the NLC ice crystals, cosmic ray interaction could be a possible trigger for their formation. As many of you know, cosmic rays leave tiny nucleation tracks, in the atmosphere. much like they do when entering a cloud chamber in a nuclear physics lab. I built one once as high school student and watched cosmic rays and other background radiation zip through.

Tracking particles and cosmic rays in a cloud chamber

As occurs in a supercooled cloud chamber (dry ice is involved) it would seem to me that cosmic ray interaction with very rarefied supercooled water vapor could be occurring in the 60-90 km altitude range. While the mechasism of a cloud chamber relies on supersaturation to leave a visbile trail, an interaction that forms a small ice crystal in the nanometer range may not need supersaturation. And, given that NLC’s form mostly at high latitudes, as aurora borealis does, there may be an interactive component of some sorts with earth’s magnetic field.

I’m also thinking NLC’s may very well be the equivalent of “dark matter in the universe” for our atmospheric interface with space and incoming solar radiation. As mentioned in the article “There is a substantial population of invisible noctilucent clouds, a population of much smaller ice crystals (< 30 nm) that don’t scatter much sunlight.” They may be small, but may have an albedo effect of some sort that is undiscovered. This is all just conjecture on my part, but I thought it would make for interesting discussion. If nothing else, NLC’s illustrate that we still don’t know how all aspects of the atmosphere work, and the portion that is closest to space is the one that is the most difficult to measure. I welcome discussion. – Anthony

UPDATE: Here is an excellent powerpoint presentation on NLC’s:

http://gwest.gats-inc.com/nlc_epo/epo_nlc_lesson.ppt

h/t to Fernando Mafili from comments


Strange Clouds at the Edge of Space

August 25, 2008: When in space, keep an eye on the window. You never know what you might see.

Last month, astronauts on board the International Space Station (ISS) witnessed a beautiful display of noctilucent or “night-shining” clouds. The station was located about 340 km over western Mongolia on July 22nd when the crew snapped this picture:

see caption

Above: Noctilucent clouds photographed by the crew of the ISS: more.

Atmospheric scientist Gary Thomas of the University of Colorado has seen thousands of noctilucent cloud (NLC) photos, and he ranks this one among the best. “It’s lovely,” he says. “And it shows just how high these clouds really are–at the very edge of space.”

He estimates the electric-blue band was 83 km above Earth’s surface, higher than 99.999% of our planet’s atmosphere. The sky at that altitude is space-black. It is the realm of meteors, high-energy auroras and decaying satellites.

What are clouds doing up there? “That’s what we’re trying to find out,” says Thomas.

People first noticed NLCs at the end of the 19th century after the 1883 eruption of Krakatoa. The Indonesian supervolcano hurled plumes of ash more than 50 km high in Earth’s atmosphere. This produced spectacular sunsets and, for a while, turned twilight sky watching into a worldwide pastime. One evening in July 1885, Robert Leslie of Southampton, England, saw wispy blue filaments in the darkening sky. He published his observations in the journal Nature and is now credited with the discovery of noctilucent clouds.

Scientists of the 19th century figured the clouds were some curious manifestation of volcanic ash. Yet long after Krakatoa’s ash settled, NLCs remained.

“It’s a puzzle,” says Thomas. “Noctilucent clouds have not only persisted, but also spread.” In the beginning, the clouds were confined to latitudes above 50o; you had to go to places like Scandinavia, Siberia and Scotland to see them. In recent years, however, they have been sighted from mid-latitudes such as Washington, Oregon, Turkey and Iran

see caption

Above: Noctilucent clouds over Mt. Sabalan, a 15,784 ft extinct volcano in northwestern Iran. Photo credit: Siamak Sabet. [more]

“This year’s apparition over Iran (pictured above) was splendid,” says Thomas. The Persian clouds appeared on July 19th, just a few days before the ISS display, and were photographed from latitude 38o N. “That’s pretty far south,” he says.

The genesis and spread of these clouds is an ongoing mystery. Could they be signs of climate change? “The first sightings do coincide with the Industrial Revolution,” notes Thomas. “But the connection is controversial.”

NASA is investigating. The AIM satellite, launched in April 2007, is now in polar orbit where it can monitor the size, shape and icy make-up of NLCs. The mission is still in its early stages, but already some things have been learned. Thomas, an AIM co-Investigator, offers these highlights:

1. Noctilucent clouds appear throughout the polar summer, are widespread, and are highly variable on hourly to daily time scales. A movie made from daily AIM snapshots shows the 2007 NLC season unfolding over the north pole: watch it.

see captionRight: A daily snapshot of noctilucent cloud activity over the North Pole in 2007. Click on the image to set the scene in motion. Credit: AIM/Goddard Space Flight Center Scientific Visualization Studio.

2. There is a substantial population of invisible noctilucent clouds. Thomas explains: “NLCs are made of tiny ice crystals 40 to 100 nanometers wide—just the right size to scatter blue wavelengths of sunlight. This was known before AIM. The spacecraft has detected another population of much smaller ice crystals (< 30 nm) that don’t scatter much sunlight.” Clouds made of these smaller crystals are stealthy and hard to see, but a key part of the overall picture.

3. Some of the shapes in noctilucent clouds, resolved for the first time by AIM’s cameras, resemble shapes in tropospheric clouds near Earth’s surface. AIM science team members have described the similarities as “startling.” The dynamics of weather at the edge of space may not be as unEarthly as previously supposed.

These findings are new and important, but they don’t yet unravel the central mysteries:

  • Why did NLCs first appear in the 19th century?
  • Why are they spreading?
  • What is ice doing in a rarefied layer of Earth’s upper atmosphere that is one hundred million times dryer than air from the Sahara desert?

AIM has just received a 3-year extension (from 2009 to 2012) to continue its studies. “We believe that more time in orbit and more data are going to help us answer these questions,” says Thomas.

Meanwhile, it’s a beautiful mystery. Just ask anyone at the edge of space.

h/t to Jack Simmons for the NASA story link.

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50 thoughts on “Noctilucent clouds and the Earth's interface with space

  1. Is there a difference by hemisphere the the amount of these clouds? Would they act as warming/cooling agents? NH arctic seems to be warming, but the SH seems to be flat or cooling. Causal or symptomatic of the warming?

  2. Hmm, at that height, when water molecules freeze, i.e. give up heat to become ice crystals, most of that heat, much more than 50% will be irradiated to space. This is a geometrical artefact.
    Understand this. Heat is transported from the surface to the upper atmosphere by convection. Heat is transfered from the atmosphere to space by radiation. The vector is moisture. It evaporates then rises then freezes. Hence clouds.

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  4. Is there any update from the Earthshine Project? I have seen several references to an increase in NLC recently.

  5. Gosh, I’m still staring at the picture. Just not ready to be technical about such a beautiful and mysterious thing. It’s like homemade bread right out of the oven. You spend some time savoring the aroma for a while.

  6. The post and ppt have certainly multiplied my knowledge of these clouds. Following up on Anthony’s intuition re: the geomagnetic influence the following are worth a look:
    http://www.es.ucsc.edu/~glatz/geodynamo.html
    http://physicsworld.com/cws/article/news/24882
    In addition, over the past century geomagnetic north has moved 1500 miles toward Siberia in the Canadian far north. This is also taken to be if not a sign of reversal (first link) a sign of reconfiguration.
    The interaction of IMF and geomagnetic fields produces geomagnetic storms 6-9 months following Solar max maximizing protection against GCRs but this interaction is at low ebb during Solar min. Yet at the same time coronal holes and CMEs are more nearly earth directed and the result is heightened Aurora activity (solar electrons) and protons, or non-galactic cosmic rays, inputting teraWatts per occasion and heating the poles. Fortuitously, the protective effect of the magnetic interaction collapses as the velocity, pressure and frequency of coronal mass ejections are also at lower levels.
    Worst case is at minimum, the orientation of IMF and geomagnetic fields can link end-to-end during a CME, which during minimum would be at least risk if likely on target.
    Perhaps the confluence of polar heating, increased convection-as Mr. Wood pointed out (stratospheric winds are also predominantly vertical)-and maximized nucleation lead to NLCs and this consequence has increased over the last century, say since the mid 1800s when the clouds were discovered and the geomagnetic field began its decline.
    Note in the ppt the two slides graphing an increase in frequency. They look rather perfectly anticorrelated to the Solar sunspot (Schwabe) cycle.

  7. Thanks Frank. Cool site.
    Looks like the clouds reside in the Mesopause, which is colder than the Mesosphere below and Thermosphere above.
    Just like the tropopause where cirrus reside between the warmer troposhere below and the warmer stratosphere above.
    If these clouds are on the increase, wonder if they will cause cooling below, even just a little.
    Very interesting.

  8. Back when I was flying, we used to see noctilucent clouds over the North Atlantic enroute to the UK at night. They looked like thin cirrus, but we were flying at cirrus altitudes and they were way higher than we were.
    Frank Ravizza’s atopics link is great. I’ve seen most of those effects while flying

  9. Talking about NLCs always reminds me of an old paper by Fred Hoyle and Chandra Wickramasinghe on the causes of ice ages. Section 3 is quite relevant in many ways. Fred Hoyle was the UK’s chief astronomer at one time, apart from a being prolific SF writer. A copy of the paper can be found here:
    http://abob.libs.uga.edu/bobk/ccc/ce120799.html

  10. Noctilucent clouds have been more frequnetly observed in the northern hemisphere than in the south:
    “They [noctilucent clouds] have been observed thousands of times in the northern hemisphere, but less than 100 observations have been reported from the southern hemisphere. It has not been resolved if this is due to inter-hemispheric differences (temperature &/or water vapour) in the atmosphere at these altitudes, or the lack of observers and poorer observing conditions in southern latitudes.”
    http://www.aad.gov.au/default.asp?casid=2005
    The NASA article makes no mention of this variability, although they make references only to observations in the northern hemisphere. The satellite data should be able to verify if there really is a hemispheric variation, so I find it curious that they don’t mention it.
    There is also some question as to whether the occurance of these clouds has really increased:
    “Noctilucent clouds (NLC) and their space counterpart, Polar Mesospheric Clouds (PMC) are water-ice clouds that form in the cold high-latitude mesopause region during summertime. These clouds have been suggested to be sensitive markers of long-term mesospheric change. It was previously reported that NLC numbers over northwestern Europe increased in the late 20th century. However, when the observations are sorted properly by location, the time series of NLC observations no longer shows an upward trend. A 40-year data set from Moscow also shows no significant long-term trend in NLC numbers, but an increase in their average brightness. There is also new satellite evidence that PMCs have brightened over the past 23 years. Recent mesospheric cloud occurrences have been reported at unusually-low latitudes (40-50 N). Together with the satellite evidence, these developments have promoted speculation that permanent atmospheric changes near the high-latitude mesopause region have occurred. Before such conclusions can be drawn, natural variations in NLC activity need to be understood. The solar cycle appears to be the dominant natural influence. The published data (both from the ground and space-based) are consistent in showing a pronounced 10-11 year period oscillation in cloud occurrence, which is approximately anti-correlated with the solar cycle. The brighter the clouds, the more their numbers change over the solar cycle. The cyclic change is likely due to small changes in mesospheric temperature and water vapor, induced by the solar cycle variation of UV irradiance. There is an unexplained several-year time lag between solar cycle minimum and the peak of cloud activity. Longer time series and more comprehensive models are needed before the link with global change can be established.”
    http://md1.csa.com/partners/viewrecord.php?requester=gs&collection=TRD&recid=A0425103AH&q=noctilucent+clouds+solar+cycle&uid=793080122&setcookie=yes

  11. I am a regular visitor to SpaceWeather.com where other readers send in pictures of interesting objects in the sky. Recently, I was puzzled by what seem to be an increase in the number of NLC photos from lower latitudes. I had seen some when flying over the arctic in the mid 60s, but they were always near the pole. I was the crew member assigned to take star shots, thus I spent a lot of time looking at the night sky on training and monitoring missions. At the time, I was thinking they were the result of our growing space program. Ice crystals from rocket exhaust. Today, I have no idea what triggers NLC development. But, they seem to be coming farther and farther down in Latitude.
    REPLY: Earth’s magnetic field has been slowly weakening, perhaps it is related.

  12. Interesting powerpoint presentation. It was going fine till slide 16 and it degenerates into the canary in the coal mine warning about global warming. Here’s a silly question: Can anybody doing any research on terrestrial occurring events manage to complete a research project without invoking global warming?
    Perhaps NLC’s were occurring before Krakatoa but were so far north that few people paid much attention to them. Then, after Krakatoa, when people paid attention to the skies and with a larger population and more scientists, the NLC’s were finally noticed. By then, they were also probably beginning their slow march south, so their discovery was more coincidental than anything.
    What if these are wholly natural events that occur at the end of an interglacial and, over the course of centuries, slowly thicken as they spread from the poles toward the equator. As well, perhaps, the period of their occurrence increases from a couple weeks to a couple months or more. Increasing strength of the event over time increases albedo, cools climate at the surface, increases polar region snow and ice which further increases albedo and in four or five centuries, voila, new Ice Age. So perhaps they are the canary in the coal mine of climate change, just not what is usually meant. Wouldn’t that be a kick in the pants?
    Wouldn’t it be nice were it that simple?

  13. I like the Hoyle and Wickramasinghe paper Doug.
    So the oceans have lost their ability to protect us from rapid decline into a future ice age and according to Hoyle and his mate “[t]his is why the past million years has been essentially a continuing ice-age, broken occasionally by short-lived interglacials. It is also why those who have engaged in lurid talk over an enhanced greenhouse effect raising the Earth’s temperature by a degree or two should be seen as both demented and dangerous.”
    Hoyle and Wickramasinghe go on to say “Ice-age conditions are dry and cold, the local temperature being reduced over the entire Earth. The high atmosphere probably had a haze of small ice crystals while the lower atmosphere was dusty.”
    So if the doomsayers find their current “carbon pollution” apocalypse slipping away from them, Hoyle and Wickramasinghe have a brand new one for them, it’s ready to roll.
    I can see it now, learned chaps from NASA (having quickly altered their names and appearance) making speeches to the US Senate warning about the dangers of “ice pollution” in the upper atmosphere – “…beware the ‘noctilucent clouds’ for they are the (new) canary in the coal mine” they’ll thunder..
    They’ll warn that “urgent methods will need to be employed to prevent ‘dangerous climate change’ or the Arctic Ice Cap will freeze all the way to Chicago and Polar Bears will roam the streets and suburbs of our cities…”
    Or am I getting too cynical?

  14. Pingback: STAY WARM, WORLD… Roger Carr « Stay Warm, World…

  15. I agree Doug, however I’m counting down to the first “demented and dangerous” member’s post demanding to know “is he peer reviewed?”
    I fondly remember “Rockets in Ursa Major” and several of his other novels. They had a considerable influence on me during the sixties and early seventies.
    I struggle to enjoy a lot of modern Sci Fi.

  16. I’ve thought for awhile that noctilucent clouds were an aurora-like phenomenon, dependent on magnetic fields. There may be a tie-in to cosmic rays on that basis. Another thing, absorption and re-emission of energy at that height acts quite a lot differently than the same processes lower down. I can’t help but think they can amplify processes.
    =============================

  17. A beautiful and well presented post, thanks Anthony.
    It’s great to know there are a lot of unsolved mysteries out there!

  18. The more we learn about the Earth, the less we know. Mother Nature still has some surprises for us. Leon touched on it: Did these clouds appear for the first time in the 19th, or did no one notice them before?
    A lot of factors may contribute: a weakening magnetic field, and moving at that. A lower solar magnetic field as well. If GCR’s are the culprit, they may be having a field day. As for NH/SH differences, apart from a lack of observers, the atmosphere over each pole differs greatly, mostly due to substantial terrain differences. North pole doesn’t have a hole in the ozone, South does.
    OT: Just saw a news note on Fox: Arctic ice melts to second lowest level on record. They never give up.

  19. Carsten:
    That’s a great scenic panorama – my congratulations. The patterns seem to imply there is as much variability in wind patterns, as high and as low a pressure as NLCs are, as there is in the troposphere.

  20. I think that would read better as “…as high UP and as low a pressure…”.
    Must be time for bed.

  21. Just some ideas:
    1. The cloud’s source of water vapor are icy meteors (often from old comet orbits intersected by the earth) burning up.
    2. Jet aircraft. If they fly in the stratosphere, perhaps some wator vapor can find its way up that high, tho that seems a stretch.
    3. Volcanic eruptions into the stratosphere, but there’s been little of that since Pinatubo.
    4. Cosmic rays. I think their flux is greater near the magnetic poles.
    5. Maybe Arctic “warming”, but it seems a stretch for that to put water vapor at such an extremely high altitude.

  22. Forgot another:
    6. Rocket launches. Yes, most occur in low latitudes, but there are some polar orbit launches. There may be enough solar radiation in low latitudes to prevent or quickly re-evaporate the condensation/freezing of trace water vapor there.

  23. Thanks for the pic Carsten – the trees in the foreground give me a much better idea of the amount of sky covered by the clouds.
    Midnight you say – I haven’t been so far north since a trip I undertook to Canada’s northern extremities during the mid 1970s.
    I fondly remember laying on the ice at midnight looking up at the aurora and marveling at its delicate beauty.
    Embarrassingly I also remember staggering back to my tent after a couple of ‘anti freeze beverages’ and cursing the poor light which caused me to stumble and lose my way ;-P
    Such is youth…

  24. “Could they be signs of climate change? “The first sightings do coincide with the Industrial Revolution,” notes Thomas. “But the connection is controversial.””
    They JUST can’t help themselves, can they?
    I would bet the the connection would be less “controversial” (more “consensus”) if there were a way to scare people with this.
    This phenomenon is also known as PMCs – Polar Mesospheric Clouds. They are formed – 50 MILES – above the surface. Hard to scare anyone with that.
    Just as a reminder, here is the Master List of everything that has been reported to be caused by “global warming,” including acne
    http://www.numberwatch.co.uk/warmlist.htm

  25. Pam is wooed by beauty
    and by the smell
    of fresh baked bread.
    From the death of pseudo-science
    she’ll be safely led.

  26. Yes Peter, I only found out Sir Fred was a real scientist many years after my SF binge of the 60s. I too haven’t bothered much with the recent crop. But then you could argue that there’s been some creative Science Fiction generated with an AGW theme in the last decade or two 🙂
    Its interesting being old enough to have experienced the “climate change” of the last PDO shift in the late 70s and to see the cycles. Oceans Rule!!
    (I’m almost embarassed to admit I worked for the down under BOM for a number of years 🙂

  27. Thank you!
    Anthony, as a layman, I hope this post opens a dialogue between the solar
    and earth scientists pursuing separate [MHO] research on the sun’s and earth’s
    respective magnetic cycles.
    I would really enyoy seeing a graph of the respective min / max of solar
    activity compared with earth magnetic field variation over time.
    Regards,
    Robert Doyle

  28. Given the size of the particles, UV light is mostly reflected by these clouds while IR radiation passes through, and visible light is attenuated?
    I know that when I worked in the Arctic and in the high mountains, high cirrus clouds made sunny days very cold ones as well. Noctilucent clouds would do the same thing.

  29. As Steve E (22:13:30) : post suggests it would seem more NLCs might be related to the Sun.
    Where I live it is often cloudy in the morning but when the Sun gets high in the sky the clouds “burn off”. And the inverse, when there is less Sun there are more clouds, would seem to be a given. Since the Sun’s intensirty is waning as we move into a new solar cycle we might expect to see more NLCs & PMCs.

  30. Sorry, can’t help myself:
    From the stark black of space
    through wrenching shades of blue
    and onto the ground
    through sad shades of brown.

  31. Back in the late 60s we trained for high level navigation by flying out to 18 or 20 W from the UK. The first trip I saw a nacreous cloud, big, fat, blobby, very white. It was fairly well above us — we were at forty fivish thousand feet. The next night in the same area was a noctilucent cloud, really high. I have wondered if the two sighting were connected.
    quote But then you could argue that there’s been some creative Science Fiction generated with an AGW theme in the last decade or two 🙂 unquote
    I ought to be grateful to AGW in a way — I wrote a short story about global cooling and sold it to Analog. A writer may gain respect from any of the big three, but only Analog brings self-respect… Thank you, Dr Hansen.
    JF

  32. Anthony;
    Your intuition is great.
    Now we have.
    1 – clouds (real)
    2 – Nuclei (true)
    3 – Correlated with solar activity
    4 – Possibly correlated with the terrestrial magnetic field.
    5 – The isotopic analysis will provide the source of water.
    The numbers of LOTTO, please

  33. We have been touching on this issue of ‘are we naturally heading toward an ice age that is being warded off by global warming’ for quite a while on this blog. I have posted a link to a Scientific American article published in 2005 titled HOW DID HUMANS FIRST ALTER GLOBAL CLIMATE?
    This article offers an alternate explanation to Fred Hoyle’s meteor on demand theory, although I wouldn’t count that out as a possibility; for the last 400K years or so.
    I keep coming back to this article because it provides an effective explanation for both warming and cooling. Here are two links to the author William Ruddiman and the article I refer to.
    http://en.wikipedia.org/wiki/William_Ruddiman
    http://www.sciam.com/article.cfm?id=how-did-humans-first-alte
    I don’t think I can reproduce the article here as Scientific American still wants payment for it but it is more than worth the read. I offer this excerpt from his conclusions which I believe is ok to reproduce (up to you Anthony).
    Implications for the Future
    The conclusion that humans prevented a cooling and arguably stopped the initial stage of a glacial cycle bears directly on a long-running dispute over what global climate has in store for us in the near future. Part of the reason that policymakers had trouble embracing the initial predictions of global warming in the 1980s was that a number of scientists had spent the previous decade telling everyone almost exactly the opposite—that an ice age was on its way. Based on the new confirmation that orbital variations control the growth and decay of ice sheets, some scientists studying these longer-scale changes had reasonably concluded that the next ice age might be only a few hundred or at most a few thousand years away.
    In subsequent years, however, investigators found that greenhouse gas concentrations were rising rapidly and that the earth’s climate was warming, at least in part because of the gas increases. This evidence convinced most scientists that the relatively near-term future (the next century or two) would be dominated by global warming rather than by global cooling. This revised prediction, based on an improved understanding of the climate system, led some policymakers to discount all forecasts—whether of global warming or an impending ice age—as untrustworthy.
    My findings add a new wrinkle to each scenario. If anything, such forecasts of an “impending” ice age were actually understated: new ice sheets should have begun to grow several millennia ago. The ice failed to grow because human-induced global warming actually began far earlier than previously thought—well before the industrial era.
    In these kinds of hotly contested topics that touch on public policy, scientific results are often used for opposing ends. Global-warming skeptics could cite my work as evidence that human-generated greenhouse gases played a beneficial role for several thousand years by keeping the earth’s climate more hospitable than it would otherwise have been. Others might counter that if so few humans with relatively primitive technologies were able to alter the course of climate so significantly, then we have reason to be concerned about the current rise of greenhouse gases to unparalleled concentrations at unprecedented rates.
    The rapid warming of the past century is probably destined to persist for at least 200 years, until the economically accessible fossil fuels become scarce. Once that happens, the earth’s climate should begin to cool gradually as the deep ocean slowly absorbs the pulse of excess CO2 from human activities. Whether global climate will cool enough to produce the long-overdue glaciations or remain warm enough to avoid that fate is impossible to predict.

  34. “Others might counter that if so few humans with relatively primitive technologies were able to alter the course of climate so significantly, then we have reason to be concerned about the current rise of greenhouse gases to unparalleled concentrations at unprecedented rates. ” Trevor Pugh
    Hmmm. Could it be that mankind is somehow special? Could it be that you know Who keeps our climate stable? Or did our campfires produce enough CO2 to ward off global cooling? I doubt the latter.
    Its all connected.
    Life is so interesting now. Dang that Chinese curse.

  35. “Thus, it appears, NLCs are another indication of climate change”
    Well, so? Waves are an indication of ocean surface change. Earthquakes are an indication of land surface change.
    I just somehow think that those last few slides were thrown in to get the further funding. Pity; spoiled an otherwise informative presentation.

  36. PeterW,
    Those renamed, newly-moustachioed, NASA types will be railing against the Hydrogen economy as it generates water vapour, and demanding the use of Carbon. Hehehe 🙂
    BTW I saw a TV ad recently for a Toyota, I think, hydrogen powered car. Environmentally friendly as it produces only H2O, not CO2.
    Hmm, I thought, water vapour is the worst greenhouse gas, isn’t it.

  37. The Powerpoint presentation is quite interesting. Slide 11, NLC Occurrence Versus Time, is quite well correlated with sunspot numbers. When sunspots are high the NLC count is low and vice versa.

  38. Slightly off topic:
    At sunset two nights ago, here in New Hampshire, I noted that, very subtle in a deep blue and cloudless twilight sky, were faint wave-clouds of the dimmest grey. At the time I wondered if ash from the Alaskan eruption in early August was passing over.

  39. What beautiful clouds! They have the same unearthly quality as the auroras. Really feel the cosmic energies tapping on our windowpane there.
    However – is anyone considering the combined effect of lower solar magnetic flux plus steadily-falling geomagnetic field? More clouds? We’ve hardly seen the Sun all August in the UK.

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