First assessment of noctilucent cloud variability at midlatitudes

This is interesting, a first dataset for noctilucent cloud variation.

Noctilucent clouds over Kuresoo bog, Viljandimaa, Estonia

Noctilucent clouds over Kuresoo bog, Viljandimaa, Estonia Image: Wikipedia

As the Sun dips below the horizon, the last rays of light can glint off crystals of ice high in the atmosphere, lighting up the sky with an electric blue glow. Known as noctilucent clouds, these collections of ice crystals occur most often at high latitudes, but the long polar days make them difficult to see. With the eye, noctilucent clouds can best be seen at night between 50 degrees and 60 degrees latitude in both hemispheres.

Investigations with other techniques, such as lidar, however, have made noctilucent clouds easier to detect during the day as well as at night. Though they show up less than 10 percent of the time at midlatitudes, noctilucent clouds are an important component of the summer atmosphere. Their properties and occurrence may indicate patterns of behavior in the middle atmosphere. 

Gerding et al. are the first to have measured the daily variation of noctilucent cloud behavior at midlatitudes from the ground. From a research site in Kühlungsborn, Germany, a town located near 54 degrees north, the authors used a suite of equipment, including lidar, to study how noctilucent clouds evolve throughout the day. From 1,800 hours of summertime observations, the authors find 100 hours that contained noctilucent clouds and observe within them recurrent daily patterns in brightness and activity. The data show that noctilucent cloud activity rises and falls with local solar time, being highest at 5 a.m. and lowest at 7 p.m., with a secondary maximum at 2 p.m. Cloud brightness peaks twice, once at 4 a.m. and once at 6 p.m.

The authors find that noctilucent cloud activity is not related to tidal temperature variation at noctilucent cloud altitudes. Rather, they find that noctilucent cloud activity for their location is highest after a bout of southward polar wind and lowest during weak or northward winds.

Source: Geophysical Research Letters, doi: 10.1002/2013GL057955, 2013 http://onlinelibrary.wiley.com/doi/10.1002/2013GL057955/abstract

Title: Diurnal variations of midlatitude NLC parameters observed by daylight-capable lidar and their relation to ambient parameters

Authors: M. Gerding, M. Kopp, P. Hoffmann, J. Höffner, and F.-J. Lübken: Leibniz-Institute of Atmospheric Physics, the Rostock University,

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10 Responses to First assessment of noctilucent cloud variability at midlatitudes

  1. mbur says:

    From abstract:
    “The simultaneously observed temperatures show a systematic (tidal) variation”
    That was interesting.
    Thanks for the info.

  2. Chad Jessup says:

    These two quotes from above, “…noctilucent clouds, these collections of ice crystals…” and “…noctilucent cloud activity for their location is highest after a bout of southward polar wind and lowest during weak or northward winds…” would make sense to me in that a polar wind would freeze more atmospheric water, and a northward wind generally emanating from the southerly tropical areas would warm the atmospheric waters, creating conditions for less noctilucent clouds.

  3. CRS, DrPH says:

    Interesting bit of information about noctilucent clouds:

    http://science.nasa.gov/science-news/science-at-nasa/2012/07aug_meteorsmoke/

    August 7, 2012:  Anyone who’s ever seen a noctilucent cloud or “NLC” would agree: They look alien.  The electric-blue ripples and pale tendrils of NLCs reaching across the night sky resemble something from another world.

    Researchers say that’s not far off.  A key ingredient for the mysterious clouds comes from outer space.

    “We’ve detected bits of ‘meteor smoke’ embedded in noctilucent clouds,” reports James Russell of Hampton University, principal investigator of NASA’s AIM mission to study the phenomenon.  “This discovery supports the theory that meteor dust is the nucleating agent around which NLCs form.”

  4. Kelvin Vaughan says:

    I am I right in assuming that the radiation from clouds is relative to their temperature and doesn’t increase in energy as it comes down through the atmosphere as the lapse rate changes?

  5. Steve Keohane says:

    Interesting, but 75 days of observation seems minimal.

  6. @njsnowfan says:

    Largest noctilucent cloud photo gallery back to 2003
    http://spaceweathergallery.com/

  7. Auto says:

    Steve Keohane says:
    March 13, 2014 at 8:56 am
    Interesting, but 75 days of observation seems minimal.

    ====

    - but it’s a start.
    I haven’t seen much on NLC variability. This paper seems almost alone, and the data is from 1997 to 2011 or 2012, so they have been trying. Germany gets rain, just like England – and you won’t see NLCs then.

    Auto

  8. george e. smith says:

    Well that noctilucent cloud article was most informative; I wouldn’t have believed clouds could form at that altitude; er um What altitude ?? Come to think of it, they didn’t say.

    I did my own cloud research project while flying from San Francisco to Generva, a week or so ago.

    From SFO across the USA/CAN, we were at from 33,000 t0 38,000 feet. At 38,000, the air temp was -68 deg C, and there were no clouds of any kind visible above us, but some really low powder puff scattered clouds, which are bright white from above, and some higher thing and wispy flat layers, still well below us. The Temperature never got above about +15 C till we were in ofrbelow those white puffy clouds.

    Across the continent, we were at about 31,000 to 33,000 and once again white puffy’s below us. So I asked the crew how high the puffy’s were, and they contacted Paris, and came back with exactly 4,100 ft.

    I’m NOT any kind of Meteor or other ologist, but my WAG, says that the white puffys are around the dew point at what ever altitude and Temperature that occurs, depending on the air moisture content, and I would guess those 4,100 footers, were all liquid water drops. And above them, there must not be much H2O. So I imagine that daytime Temps evaporate a lot of water vapor, which rises to the dewpoint altitude, and then condenses to white puffys, which stay at that altitude, and very little of the new moisture moves above there.

    If there is higher moisture from wherever, including plane vapor trails, it is at much higher an much colder below freezing Temps, so is all ice crystals.

    Now water droplets are pretty spherical, and low absorbing of solar spectrum, but highly refractive scattering, hence the diffuse apparent reflectance.

    But ice crystals are not spherical, and I imagine they are considerably more absorptive, of solar spectrum, because of TIR trapping (total internal reflection) . So I would expect their solar energy absorption to be higher than for the white puffys, so they would heat a bit more (and go higher) .

    I’m not sure it makes much difference as to LWIR upward radiation from the surface, that is so strongly absorbed, that it is probably not so much optical trapping, as molecular absorption.

    It was a little but not much bumpy around the white puffys, so the scattered Cloud nature is likely due to the general turbulence of the air, due to local Temperature differences.

    Well just a WAG remember, I’m not predicting anything.

    But my feeling is that water in the atmosphere, is anything but well distributed.

    The vapor trails, fall into two classes, those that evaporate, after a few km of length, and those that grow and spread into wide flat cloud layers. Probably depends on the local ambient, relative humidity.

  9. Carbomontanus says:

    To all and everyone

    It is not as easy as that, but george e smith has noticed a lot of important things.

    That tropopause for instance, the cool side of the globe, is where understanding of the climate should start.

    Give that sharp knick in the lapse- rate worldwide with ist quite incredibly low temperatures even with the sun right in zenith , its true natural and physical explaination first, and it ruins the very CO2-AGW Climate- denial hype or religion.

    The same phaenomena measures -40 celsius on Venus, right in the very sharp direct sunstitch there..

    It freezes out practically all water from below. For airplanes to burn kerosene at that rate in that thin air less than 1/4 of normal, takes a really good turbo compressor.

    That same tropopause is the field of the world fleet of civil commercial and market economical jetliner traffic, thus consequentely hidden and shown avway from by the denial moovement.

    CH4 , a non condensing climate gas, passes through the tropopause and mixes up higher where it is oxidized into CO2 and 2 H2O by UV- light and ozone.

    But 2 other important gases also pass. SO2 and N2O. they end up into HNO3 and H2SO4.

    I red somewhere that the ice crystals are actually støchiometric crystals of H2SO4 . HNO3 .H2O

    they are quite Extreemly hygroscopic in any case , else they could not cristallize out of that very thin air with very low H2O gas partial pressure.

    The idea of “stardust” contributing is one of my own suggestions and questions also. It must be shown positive and NASA seem to have done it.

    But it ruins also at the same time the fameous Svensmark hypes, if even “stardust” has got a lot to say. That stardust comes from the solar system and not from the “galaxy”.

    I would rather set on UV and X- ray from the sun being further responsible for charged nanoparticles on which H2O- gas can further freeze and condense. With the very good help of strong sulphuric acid.

    My record is having seen -70 C on the termometer outdoor at 12 Km heighth at bright daylight in the afternoon south of Island, at autumnal eqvinox.

    There were records of NLC in the norwegian astronomical society in 2003-2004.

    I tried with the reflex in a common window glass. The sheere indigo bluelight is definitely not polarized, but polarized light comes from the clear deep blue or violet sky beneith them.

    And the astronomical society tells that they show Fraunhofer- lines. Then it is definitely diffuse reflected sunlight. And definitely not fluorescence from the particles themselves.

  10. dbstealey says:

    Carbomontanus says:

    “…george e smith has noticed a lot of important things.”

    George’s posts are always worth reading, IMHO.

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