APOD: Jumping Sundogs Over Thunderclouds (2011 Nov 08)

[neufer]

Is the bright spot in the video actually a sundog (that is, a reflection from aligned ice crystals, 22° from the Sun), or a reflection from an isolated patch of ice crystals? I've seen both (but not dancing), and since I can't tell where in this image the Sun actually is, I can't tell if this is really a sundog.

[size=200][color=#FF0000]22° from the Sun[/color][/size] :?:

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<<Guinness Book of World Records holder John Cassidy performs a balloon act for First Lady Michelle Obama in the Diplomatic Reception Room of the White House, Oct. 11, 2011. Cassidy performed for kids on the South Lawn before the First Lady launched a challenge to break the Guinness World Records title for the most people doing jumping jacks in a 24-hour period.>>

[iamlucky13]

A related phenomenon is that often during a thunderstorm, after a nearby lightning stroke, the rainfall suddenly becomes more intense. I figure that's because the raindrops are carrying negative charge down to the ground, building up positive charge in the clouds. The drops fall against that field, as makes sense because they are increasing the energy in the electric field. A lightning stroke between sky and ground drains off some of that charge and reduces the field, thus causing the drops to fall faster. Since a typical change in the electric field can have that much effect on many tonnes of water, I can well believe that it can rapidly affect the orientation of ice crystals in a cloud.

I don't know if the increase in rain immediately after a lightning strike is a real effect or a misconception arising out of observation bias (if it's random, you can assume half the time the rain intensity tends to increase after a strike, and half the time it tends to decrease, but a person observing the process anecdotally may not tend to notice the decreases as consistently).

However, you may be contemplating a realistic mechanism for this to happen.

I tend to think a more likely explanation would be a change in the electric field in the cloud after a strike may reduce electrostatic repulsion of small droplets, allowing them to merge into larger droplets more easily.

[hwelborn]

This is utterly fantastic.

[geckzilla]

Fascinating ,but how come the clouds don't seem to be moving ?
One would think that over the duration of the video there would be some change
in the cloud shapes.

Just jump between the beginning and the end of the video and compare the shapes of the clouds. They change quite a bit.

[ddorn777]

Wow! That's just freaky looking!

Thanks for the cool video. I look up every day, and try to see what the Halos are doing, if anything. I've never seen anything as unique as this.

[PParke]

Your theory about ice crystal orientation being suddenly affected by rapid changes of electrical field due to lightning is interesting. It so happens that the National Weather Service (NWS) is beginning implementation of a Dual-Polar Doppler-Radar system. The NWS is in the process of developing some products from this system that compares vertical polarization with horizontal polarization of both ice crystals and precipitation. So far, NWS research has found sharp bands of contrasting values where dual-polarized radar beams intersect ice crystals around the tops of thunderstorms. These ice crystals have been found to change orientation suddenly and across short distances due to lightning discharges. To my knowledge, all of this sort of research is "public domain" and such brand-new products will gradually become more widely available as they are perfected by further research and become more widely developed and introduced. Perhaps you might keep an eye open for near-future research and development from this direction.

[neptunium]

Neufer, that's just odd in so many ways.
Amazing video! Pretty cool how that can develop from thunderclouds.

[wbeaty]

Is the bright spot in the video actually a sundog

Nope, it seems to be a Pileus cloud above a thunderhead.

"Sundog" refers to one of the videos listed on http://amasci.com/amateur/sundog.html, specifically this one:

http://www.youtube.com/watch?v=fEiQKOLXU8Y

I'd think that in general, if you were interested in this phenomenon, you'd want to look for reflective areas around thunderclouds, not usually at sundogs (which aren't usually present when there are thunderclouds).

Yes, most of the various youtube videos of the phenomenon are fairly obviously *not* sundogs.

[wbeaty]

The NWS is in the process of developing some products from this system that compares vertical polarization with horizontal polarization of both ice crystals and precipitation. So far, NWS research has found sharp bands of contrasting values where dual-polarized radar beams intersect ice crystals around the tops of thunderstorms. These ice crystals have been found to change orientation suddenly and across short distances due to lightning discharges.

Apparently the changing radar reflections were an old observation pre-1996:

http://ieeexplore.ieee.org/xpl/freeabs_ ... ber=508402

In 1965 the optical version was reported by B. Vonnegut in the journal "Weather"

"Orientation of ice crystals in the electric field of a thunderstorm" - Weather, 1965

2002 paper on e-field values necessary to align plate-like suspended ice crystals:
http://www.sciencedirect.com/science/ar ... 950200008X

[Guest]

IMHO, and in concordance with seasoned atmospheric optics observers, I must say the jumping sensation CANNOT be a sundog, as there is no color at all. My question would be, whether the vid has been taken through a window with maybe a water drop on top to produce an image ghost.

Elmar Schmidt

[wbeaty]

IMHO, and in concordance with seasoned atmospheric optics observers, I must say the jumping sensation CANNOT be a sundog,

Again, "sundog" refers to the first video in the list of six in the first link.

as there is no color at all. My question would be, whether the vid has been taken through a window with maybe a water drop on top to produce an image ghost.

Which vid do you mean? There are several, from different years and different sources. Weather physicist Bernard Vonnegut seems to have been first with the electrostatic explanation, with his paper in the journal "Weather:"

ORIENTATION OF ICE CRYSTALS IN THE ELECTRIC FIELD OF A THUNDERSTORM
Bernard Vonnegut 1965
An interesting and unusual optical phenomenon associated with a thunder-cloud is reported and discussed by Hale(1950), Ludlam(1950), and Lacy(1950). Early in the afternoon a thundersloud viewed from the north was observed to form a 'bright streamer apparently of cloud projecting northwards from the anvil.' This streamer repeatedly built up slowly and then suddenly disappeared apparently at the same time as a lightning discharge took place. When I recently came across the report of these observations, I was struck by their similarity to an interesting electrical phenomenon that can readily be demonstrated in the laboratory using the elegant cold-box technique devised by Schaefer(1946). It appears worth describing this possible laboratory analogue to the thunderstorm phebnomenon for it adds yet another possible interpretation to those that have already been suggested by Ludlam and Lacy... [experiment with illuminated ice platelets, w/bright spot shifted by a charged ebonite rod]

Here's mention in Nature from 1971: http://www.nature.com/nature/journal/v2 ... 184b0.html

[katy]

What the heck is it my computer blocks youtube CAN ANYONE TELL ME WHAT IT LOOKS LIKE BECAUSE I LIKE TO SEE THE ASTRONOMY PICTURE OF THE DAY EVERYDAY HELP!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[katy]

What the heck is it my computer blocks youtube CAN ANYONE TELL ME WHAT IT LOOKS LIKE BECAUSE I LIKE TO SEE THE ASTRONOMY PICTURE OF THE DAY EVERYDAY HELP!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[SJoe]

WAY COOL! It's not very often that APOD actually teaches us something new--or at least something we didn't know before. Keep up the great work.

I learn something new everyday when I visit APOD.

[wbeaty]

What the heck is it my computer blocks youtube CAN ANYONE TELL ME WHAT IT LOOKS LIKE BECAUSE I LIKE TO SEE THE ASTRONOMY PICTURE OF THE DAY EVERYDAY HELP!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

The video shows bright bands ?cirrus? next to a thunderhead, and the bright parts are jumping around every few seconds. It's probably one of these seen from below: http://apod.nasa.gov/apod/ap110824.html

[Chris Peterson]

The video shows bright bands ?cirrus? next to a thunderhead, and the bright parts are jumping around every few seconds. It's probably one of these seen from below: http://apod.nasa.gov/apod/ap110824.html

No, iridescent clouds don't jump around that way. They are stable for minutes or longer.

[wbeaty]

> No, iridescent clouds don't jump around that way. They are stable for minutes or longer.

Read the main entry again, I believe you've missed the entire point: the cloud in the videos aren't jumping. The sudden motions in all the various different videos are obviously not motions of clouds. (Especially in http://www.youtube.com/watch?v=fEiQKOLXU8Y where the bright patch briefly jumps a significant distance in a fraction of a second.)

As mentioned by Vonnegut 1965 http://bit.ly/sXjwYK, only the reflected bright spot jumps, while the distribution of suspended particles remains stable over minutes. This phenomenon turns out to have been reported by eyewitnesses for many decades, and been written up in the literature several times, but only recently do we have some video evidence.

Ah, also I referenced http://apod.nasa.gov/apod/ap110824.html as an example of Pileus: suspended ice crystals above a thunderhead, not necessarily iridescent.

The real question is, why aren't there hundreds of videotaped events like this, rather than just four? One obvious possibility: the bright patch caused by electrically-aligned crystals would only be visible over a fairly small angle, so the sun would have to be at the right height above horizon, and the eyewitnesses would have to be in the right place on the ground relative to the reflective cloud. And of course the cap-cloud would have to contain crystals.

[John G. E.]

I'd like some reassurance that this video was not taken through a window or a skylight. Some of the light changes do not look like they are associated with the cloud at all to me.

[Chris Peterson]

Read the main entry again, I believe you've missed the entire point: the cloud in the videos aren't jumping. The sudden motions in all the various different videos are obviously not motions of clouds.

I understand that. You apparently suggested via a link that we are seeing an iridescent cloud in this video, which we are not.

The real question is, why aren't there hundreds of videotaped events like this, rather than just four? One obvious possibility: the bright patch caused by electrically-aligned crystals would only be visible over a fairly small angle, so the sun would have to be at the right height above horizon, and the eyewitnesses would have to be in the right place on the ground relative to the reflective cloud. And of course the cap-cloud would have to contain crystals.

I think the reason is that the phenomenon is fairly rare, and until recently, video cameras have not been ubiquitous. Now that everyone is walking around with one, I expect more videos like this will start showing up. I don't think that the phenomenon is visible over just a narrow angle, however.

[radii]

Someone from the ground is aiming a beam up there causing temperature variants and changes in the clouds and intense reflections - probably some college kids at a university in the astronomy dept.

[geckzilla]

[TNT]

Someone from the ground is aiming a beam up there causing temperature variants and changes in the clouds and intense reflections - probably some college kids at a university in the astronomy dept.

How is that possible? We don't even know the temperature up there IF that happened, much less how much it varies. That is a cumulonimbus cloud, which only changes its type, not its form, unlike cumulus clouds, which grow into cumulonimbus clouds. Furthermore, what reflections are there? And why do you think that college kids in the astronomy department would do that?

[bystander]

HAARP! Haven't you been listening to all of the conspiracy rumors. It's responsible for everything from earthquakes in Oklahoma to mind control.