APOD: Mysterious Green Patches on the Sky (2013 Sep 30)

[men in white]

Hi there, I'll try a guess.

What we see look like polar aurora i.e charged particles moving in the ionosphere.... Except we are not in the poles.
Also we know some experiment like HAARP (High frequency active auroral research program) could interact via HF radio wave with the ionosphere.

It could be a side effect of such experiment.

[G Williams]

I would guess that whatever the steady light source is to the right illuminating the rocks is causing a reflection of a sort off the water as it covers the beach.

[Ahmad]

I am now very inclined on a HDR side-effect: see how the colors of the other objects (e.g. rocks, distant horizon etc.) are re-mapped.

[Gordojenks]

Looks like light cloud cover has moved through the area.

[terrastro]

It is hard to tell on a low resolution video with saturation levels as high as they are but I would guess that it is airglow. I have seen in on a number of my timelapses and it can change reasonably quickly.
Here is one example from 2012 (view full screen):


The pattern can be more easily seen in the negative image and the sweeping action happens around 00:35 mark.

Cheers,
Alex

[terrastro]

This airglow thing is confusing to me. I've never heard about it until the last few years. Has airglow become much more common lately? Has man-made pollution something to do with it?

Ann

Ann, I think it is bevcause the consumer cameras became more sensitive and there are a lot more wide-field timelapses now that show it very well.

[thailazer]

It occurs early in the morning when the temperature is the lowest, so my suspicion is that water vapor is reaching the dew point. Not sure why it appears green but the look and flow of it is similar to clouds forming in the mountains.

[PeterLL]

Judging from the movements of the stars, this view is looking roughly south, so the Aurora seems unlikely even from this latitude. The Sun was about 22 degrees below the horizon at the time (about 0200 local solar time - I assume times are local solar, but are they an hour ahead?). Noctilucent clouds are most unlikely to the south too. To me the light looks like reflection from clouds, but from where and why green? What causes skyglow?

[patcon]

Seems just like Aurora seen off the coast of Norway late last year. It would not be at all unusual to see it in Canada, especially as we are in a maximum sun activity period.

[Briton Meterological]

(from spaceweather) Airglow resembles the aurora borealis, its underlying physics is different. Airglow is caused by an assortment of chemical reactions in the upper atmosphere. During the day, ultraviolet radiation from the sun ionizes atoms and breaks apart molecules. At night, the atoms and molecules recombine, emitting photons as they return to normal. This process produces an aurora-like glow visible on very dark nights.”

[anobium]

My entirely uninformed opinion inclines to the simplest answer, which is the aurora.

[Nitpicker]

Well, my re-reading of this entire topic leads me to believe that, as an exercise in testing the collective intelligence of this forum's contributors, we haven't been very decisive (especially me). Several people have been convincing, but I'm not sure that a majority have been convinced.

One point which hasn't yet been emphasised is that each split-second frame in the video represents 30 seconds of exposure, and the green patches were not apparent to the naked eye. In other words, the green patches are a very dim phenomenon. Also, the lack of apparent banding, which is supposed to rule out air-glow, could simply be because of the way this time-lapse has been recorded and presented.

Putting aside artificial possibilities for a moment (still a real possibility), if it is a question of aurora versus air-glow, I think the dimness would have to make air-glow more likely.

[johnsalterego]

The video seems to have a bit of green chromatic aberration to it anyway, which may effect the color of the patches. My guess would either be Aurora, or light reflecting off of wispy clouds in the atmosphere.

[erhoads]

I would go with aurora. This was taken in Canada afterall.

[LMGCUMC]

I vote for back-lighting source reflected on the rocks then being reflected by the incoming tide onto the earliest incoming clouds before thicker clouds then block that out.

[dkidroske]

Due to the timing of the phenomena, I'd say it is a scattering of light due to the sunrise.

[p40whk]

Visually, it looks just like an Aurora. Especially how it dances across the sky which is something that can usually only be captured with long exposures as Auroras move so slow that the naked eye can just barely perceive movement.

[BRC]

It appears at the same time the surf come up and seems to be a reflection from the surface of the water.

BRC

[mapwriter]

Lovely, whatever it is

[steve91949]

There was a CME reported three days earlier on August 8, 2013. See http://www.youtube.com/watch?v=AJ1FYPKj5qA. My bet is on an aurora caused by arrival at earth on the 11th.

[cathalferris]

The green patchy moving glow - the simplest explanation is that it is airglow. The movement is about the right rate compared to other videos that I have seen of the phenomenon.
Things that discount the other suggestions above:
There is no dimming or enlargement (halo) of background stars until the visible clouds roll in at the end from the right, so we can discount a high mist or cirrus.
The clouds rolling in at the end are not illuminated by a green light, but look as they are lit by standard high pressure sodium lighting, again discounting a local illumination of a nearby or distant cloud.
If there was a light source within a few hundred metres of the camera, that was bright enough to illuminate a distant mist, there would be significant backscatter visible from the outbound beam and this is not being seen in the exposures. If the exposures were able to pick up any reflected light from clouds a few km away, the outbound beam would certainly be picked up as well. So we can discount any local illumination.

This leaves aurora and airglow.
Aurora don't move linearly that often when in patchy sheets with structure. If the aurora was bright enough to have structure visible, generally there would be more sinuous motions as well as more vertical components through the upper atmosphere. the camera location is at a similar geomagnetic latitude to my own location, and there weren't any notable aurorae captured that night around where I was. Also the Kp that night didn't get above an estimated 3, and Kp of at least 5 or greater would be needed to get overhead aurorae at that location. The CME didn't have any significant effect.

Airglow generally appears as a patterned sheet that moves across the sky in a similar appearance to clouds, but at the mesosphere/ionosphere level. Everything about the green glow is consistent with airglow, and I'm not seeing behaviour of the green glow that is not consistent with it being airglow.

(To answer the question above about the more recent visibility of airglow compared to previous decades, the ubiquity of decently efficient digital sensors has made it possible to ordinary people to be able to capture such low light glows as airglow with little trouble, and the ability to do half-decent post-processing makes any glows more visible as well. Previously things like photomultiplication tubes would have been needed to see the glows. We're seeing more, doesn't mean that there are more.)

[cisackson]

There are too many colors in the shot to make a clear decision. Green seems to sweep off the right-most rock as we get into the darker part of the evening. Too bad a similar set of shots is not available without the light-up foreground as that would have been the real test to see what may have been sensed by the camera without the artificial lighting. For me, the artificial lighting added too many variables.

[#freshswag]

There is clearly a party going on behind the Hopewell rocks...and as the tide comes in it reflects the dance party lights from around the corner.

Or there are aliens

[Canadian Grandma]

As the green appears to mimic the ripples of the incoming tide, I think the hidden light source is reflecting off the water onto the camera lense itself.
Joyce

[Kver]

It appears to me that it is a reflection of a green aurora (out of frame possibly to the right) on some higher level clouds. The condensation/evaporation or perhaps deposition/sublimation of ice at higher levels of the atmosphere would appears as or like this. Some cirrostratus clouds perhaps before the lower level stratus clouds. The green color matches many auroras.