What caused the strobe effect on the raindrops during the thunderstorm?

  • Thread starter GENIERE
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In summary, during a heavy, nighttime rainstorm, a person observed a strobe effect on some raindrops as they fell. After some discussion and theories, it was discovered that this effect was caused by the oscillations of the raindrops as they fell, creating a "scintillation" effect in the light reflected off of them. This effect was observed to be more pronounced with larger, faster-moving droplets.
  • #1
GENIERE
I opened the garage doors and turned on a pair of 150-watt incandescent (note INCANDESCENT) floodlights to admire a torrential thunderstorm and newly created river rushing down my driveway.

What amazed me most was a strobe effect on some of the raindrops. There was little or no wind, the droplets seemed to fall at 4 different rates. The slowest, presumably smallest, fell only a few feet per second like very fine snow. The next fell at a rate that one could track continuously as it passed through the floodlight beam. Others seemed to draw a line as they passed through the beam similar to a meteor trail. The fastest drew a DIScontinuous line as they passed through the beam. As they passed at about two meters in front of me, they formed a broken line segment about 2 cm bright, 2 cm invisible, exactly as one would observe if they were illuminated by a strobe lamp. The only illumination was the incandescent flood lamps (no dimmer in circuit). The strobe effect seemed only to occur with the fastest (largest?) droplets.

I can’t think of anything that would cause this.
 
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  • #2
Drugs?[color=#eded]...[/color]
 
  • #3
Danger said:
Drugs?[color=#eded]...[/color]

No thanks.
 
  • #4
Maybe you are seeing different droplets reflecting light to your eyes..maybe a few different droplets appear as one droplet dropping to the ground. Just a theory...
 
  • #5
Maybe there is a slight strobe like effect from the incandescent lights due to the alternating current of the power source?

"[URL ]http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00Bh5c&tag=

This page seems to support this hypothesis.
 
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  • #6
Link busted (an extra http// in there). Here is the correct link:

http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00Bh5c&tag=""

Unfortunately, it does NOT support the strobe hypothesis, since the objects in the SUV picture are not being lit by any strobe source.
 
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  • #7
I put forth the following hypothesis:

The first three size of drops are not doing anything out of the ordinary:
- Small drops are falling slowly like snow,
- Medium drops are falling fast enough to track,
- Larger drops are falling fast enough to be a blur
So, the only thing needing explaining is the fourth type, the discontinuous line.

I submit that the discontinuous trails are a trick of the eye. The eye does not move smoothly, but jerks very rapidly - faster than we are conscious of. This is known to produce stroboscopic effects under the right circumstances.

I'd go further, to suggest that the difference between types I-III and type IV is a matter of what you are trtying to focus on - something moving or something still. I'd bet that you couldn't see types I-III and type IV simultaneously (though you may not realize it).
 
  • #8
Duncan said:
…Maybe there is a slight strobe like effect from the incandescent lights due to the alternating current of the power source?

It seems a camera can detect the warming cooling cycle and I have seen he effect on film before but never took note of it. I just now dimmed a halogen lamp using a common residential dimmer control. I dimmed it to the point where it extinguished if dimmed any further. I could easily count the turns in the coiled filament. I could not discern any flickering even if I shook my head rapidly.

DaveC426913 said:
…I submit that the discontinuous trails are a trick of the eye. The eye does not move smoothly, but jerks very rapidly - faster than we are conscious of. This is known to produce stroboscopic effects under the right circumstances.

Any links?
 
  • #9
Try waving your hand rapidly back and forth in front of the light source, Geniere, and compare with the same in front of the TV in a darkened room.

Oh go on then, I've just run out back and looked at the spray from the hosepipe in torchlight. There did seem to be something of a morse-code effect with some dots and some dashes. Interesting.
 
  • #10
Farsight said:
…Try waving your hand rapidly back and forth in front of the light source, Geniere, and compare with the same in front of the TV in a darkened room.
Been doing that since 1946 when my dad got our first TV.
Farsight said:
…Oh go on then, I've just run out back and looked at the spray from the hosepipe in torchlight. There did seem to be something of a morse-code effect with some dots and some dashes. Interesting.
Using a garden hose (good idea-thanks) and floodlights I was able to duplicate the strobe effect. It required adjusting the hose nozzle to obtain large droplets. The effect was not quite the same in that the bright/invisible components of the trail were about 4cm rather than 2cm. I attribute that to the droplets moving slower.

My 3 million candlepower flashlight (torchlight?) decided not to work tonight so I tried to use my SUV’s headlights to eliminate the possibility of the effect being caused by 60hz ac power. Using the garden hose and the headlights, I did discern the effect; at least I think I did. I need to find a way to eliminate glare and use a wider part of the beam.

My theory of the moment is that the droplets are oscillating as they fall
 
  • #11
GENIERE said:
My theory of the moment is that the droplets are oscillating as they fall
Oscillating how? And how would that cause the effect?
 
  • #12
Drugs?... ...
 
  • #13
No longer stumped!

No longer stumped!

http://www.highbeam.com/library/docFree.asp?DOCID=1G1:3670324
“Moreover, there is evidence that raindrops can take on other shapes and that they actually oscillate from one shape to another while they fall. Under the right conditions during a heavy, nighttime rainstorm, anyone can see the effects of these oscillations,…Illumination of rain at night reveals scintillations in the light reflected from the falling drops," says Beard, " with the drops often appearing as dashed streaks… Each raindrop behaves like a little falling lens. Light from, say, a floodlight shining against a dark background bends as it enters each droplet and is reflected back out. As the lens oscillates, the light is reflected in different directions. Thus, a stationary observer sees the bright, reflected light only for brief intervals, when the light happens to go in the viewer's direction. This creates the illusion of broken streaks of light.
 
  • #14
Good one, Geniere. We learn something new every day!
 
  • #15
Wow. Talk about getting the answer to your question...It's like they wrote that just for you.
 

What caused the strobe effect on the raindrops during the thunderstorm?

The strobe effect on raindrops during a thunderstorm is a fascinating phenomenon that has puzzled scientists for years. Here are five of the most frequently asked questions about its cause and some possible explanations.

1. Is the strobe effect caused by lightning?

While it may seem logical to assume that lightning is the cause of the strobe effect on raindrops, it is not the only factor at play. Lightning does produce a burst of light that can create a strobe-like effect, but it is not the sole reason for the phenomenon.

2. Could it be caused by the raindrops themselves?

There is some evidence to suggest that the shape and size of raindrops can contribute to the strobe effect. As raindrops fall through the air, they can create a disturbance in the air around them, which can cause light to be refracted in many directions, resulting in a flickering effect.

3. What role does the angle of the light play in the strobe effect?

The angle of the light can have a significant impact on the intensity of the strobe effect. If the light is coming from a low angle, it can create a more pronounced strobe effect as the raindrops are more likely to reflect the light directly back to the observer.

4. Are there any atmospheric conditions that can contribute to the strobe effect?

Yes, atmospheric conditions such as humidity and temperature can affect the strobe effect on raindrops. Higher levels of humidity can result in more water vapor in the air, which can contribute to light refraction and create a more intense strobe effect.

5. Can the strobe effect be replicated in a laboratory setting?

While scientists have been able to recreate some aspects of the strobe effect in a laboratory, it is challenging to replicate the exact conditions of a thunderstorm. The complex interplay of lightning, raindrops, and atmospheric conditions make it difficult to recreate the strobe effect in a controlled environment.

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