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Featured I Lightning discharge's effect on rain fall velocity?

  1. Dec 5, 2016 #1
    When stopped at a red light during a thunder storm, I notice this:

    - I hear the intensity of the rain hitting the roof of the car
    - there is a lightening flash
    - for a couple of seconds the rain intensity eases up noticeably, then resumes
    - then the thunder clap follows a little bit later

    It is as if the velocity of the rain slows down immediately after the lightening discharge, as if all the rain drops were briefly experiencing a little upward pull for a second or two.

    I know that rain is charged and the lightening is a discharge, and both are relative to the ground, I think, but I don't know the relative polarities... is there some way that the charged rain drops are being momentarily attracted upwards by the lightening or its regional effects?

    Could it be that the metal car itself is altering its charge and somehow repelling the rain charges for a moment?
     
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  3. Dec 5, 2016 #2

    Nidum

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  4. Dec 5, 2016 #3

    A.T.

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    Try to record it with a cell phone or something. It could be just a psychosensoric effect.
     
  5. Dec 5, 2016 #4

    CWatters

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    I'd not heard of this effect before so I went googling and found this...


    http://onlinelibrary.wiley.com/doi/10.1029/JC079i018p02699/abstract

    I've not paid for full access but it seems that electrical charge can reduce rainfall before a strike occurs and increase it afterwards. There will be some time shifting depending on where you are in relation to the strike.
     
  6. Dec 5, 2016 #5
    I have not noticed that.
    I have noticed that sometimes there is a gush of rainfall after the thunder.
    Good observation.
     
  7. Dec 5, 2016 #6

    mfb

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    They describe exactly the opposite effect:
    "It is widely accepted that a heavy shower often follows a lightning stroke"

    The basic idea: Larger negative particles accumulate at the bottom of the cloud, smaller positive particles accumulate at the top. The resulting electric fields provide some upwards force on raindrops at the bottom, lightning discharges the electric field, raindrops start to fall. Over time, the electric field builds up again, slowly reducing the rate of rain.
    Note that this increase starts in the clouds - it takes a while until the increased rainfall rate reaches the ground.
     
  8. Dec 5, 2016 #7

    davenn

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    rainfall rates will vary greatly during storm activity regardless of if there is localised lightning or not

    yes it did :wink:


    interestingly, as having been a stormchaser for many years, I can say that I have never observed that effect
    even in my latest storm chase, yesterday 05 Dec.

    The heaviest rainfall and the lightning will ALWAYS be assoc with the core of the storm cell

    and just to show an example of that ... from one of the radars and lightning trackers, here in eastern Australia, yesterday

    just radar ..... the yellows, reds and purples are the cores with yellow the least intense and purple the most intense

    Clipboard01.gif

    below with a lightning overlay
    note the white lightning strikes ( the most recent ones) occur around the cores of the various cells
    (the blue, red and purple lightning strikes are the older ones )

    Clipboard02.gif


    Dave
     
  9. Dec 5, 2016 #8
    The gush is interesting, but the effect I observe is distinct - a brief calming of the rain immediately after the strike. I am more and more wondering if the metal car is part of the effect, not so much the whole region around me.
     
  10. Dec 6, 2016 #9

    A.T.

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    Do you actually have an objective measurement, or just your subjective impression?
     
  11. Dec 6, 2016 #10
    My ears are measuring the level of noise the rain makes against the roof of the car. The drop in the noise level is a clear difference. As a musician and audiophile, I would estimate the drop approaches -15dB. If I had a recording of it (but I don't), and I listened to it, would you ask me if what I heard on the recording was my subjective impression? If you listened to it would you ask yourself that question after definitely hearing it? Or would you need to measure the change in voltage of the signal? :)

    Something is definitely happening to the rain drops - they are being lifted by a sudden change in charge so their velocity slows, or repelled from the car chassis and slowed, or they are being dispersed into smaller quiet drops right before striking the roof of the car... or something. The gushing topic makes me hopeful there is a similar but opposite principle here.

    In the mean time, it must be raining for some of you... if you find yourself stopped in the car during a lightening storm please see if you notice this effect.
     
  12. Dec 6, 2016 #11

    mfb

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    A computer can easily measure the sound level, that is much more objective. There is also the option to try the reverse: Listen to the sound only and then figure out when lightning strikes happened.

    As discussed: Lightning changes the electrostatic environment, and raindrops can be charged, so in general there can be an effect. The effect discussed in the paper is relevant for the clouds, at the ground there could be something different happening.
     
  13. Dec 6, 2016 #12

    davenn

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    like I said, the rainfall rates vary greatly and regularly within a storm cell .... I would really be surprised if there was a connection
    Even the swirling winds usually present in a storm can change the way the rain falls

    during my stormchasing, I am in that situation often
     
  14. Dec 7, 2016 #13
    Could it be that the rain drops around the thunder got evaporated so the rain "stopped" until the arrival of the next bunch of rain drops?
     
  15. Dec 7, 2016 #14
    If you mean the rain around the lightening, that absence of rain would be far away... the rain that is already over me would still continue.
    The let up of the rain immediately after the flash means to me that either the effect is regional (all the rain is easing up or dispersing into smaller droplets) or that the effect is local to me (the car's charge relation to the drops right above me).
     
  16. Dec 7, 2016 #15
    Yeah for some reason I assumed this happened near you but then I read again that you heard the thunder later on, so if you were near the lighting this would have happened almost simultaneously :P
     
  17. Dec 7, 2016 #16

    A.T.

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    Not objectively.

    I would look at the waveform in an audio software.
     
  18. Dec 7, 2016 #17
    - is it possible that vasoconstriction accompanies the closing of the iris from bright lights and thus being a mechanism whereby there is a temporary hearing impairment. - is it possible a musician has a kind of learned response to bright lights followed by or accompanied by loud noise resulting in said vasoconstriction.
     
  19. Dec 8, 2016 #18
    15 years ago a thunderstorm had just passed over, the wind had stopped, humidity was 100% and the sun had come out when there was a huge flash of lightning. I was on the phone to a friend at the time and he heard the thunder clap first through my phone and I heard it again seconds later through his phone. From knowing both our locations I had a fair idea where it hit so I went outside and took 2 photos, from different locations, of what looked like smoke coming up in the direction of the lightning strike. It's a real pity that I don't have the photos now as they both showed a dark fuzzy straight line from the top of the photo to the small amount of white smoke coming from the top of a chimney stack that had been hit. I only noticed the dark fuzzy lines when I zoomed in on the images to see the source of the smoke. I also noticed that the 2 lines had slightly different angles due to the 2 different locations from where the photos were taken.

    In this case the discharge only impacted noticeably on the water vapor in close vicinity to the lightnings path.
     
    Last edited: Dec 8, 2016
  20. Dec 8, 2016 #19

    Baluncore

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    Electric charge on rain drops in a cloud fall with those drops to the base of the cloud. Below that point the water usually evaporates and so leaves many ionic nuclei concentrated near the cloud base.

    A fall of melting hail or large drops from high above may pass through the cloud-base. As that heavy downpour approaches the ground, the charge carried from the cloud-base discharges across the gap from the descending parcel of saturated air to the Earth's surface. Shortly after the first strike, the downpour of recently discharged heavy drops that carried the charge downwards reaches the surface. That is why the lightning strike precedes the first unusually heavy downpour.

    The first downpour is self-limiting, the falling drops, with attached air, moves as a parcel with the following higher drops catching up with the lower leading drops. A surrounding updraft, induced by the falling parcel of air, cuts off the parcel from the air above. That explains the tapered end to the first heavy downpour.

    After a short delay, a steady rain begins to fall throughout the area. If the first strike facilitates the following steady rainfall, then an explanation is not obvious to me. It is I think more likely that the steady rain is falling slower than the heavy downpour that fell faster and so caused the first lightning strike.
     
  21. Dec 9, 2016 #20

    davenn

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    clear air strikes are not uncommon. A lot of people don't know that and think because the storm has passed they are safe. MOST of the time they are. But from time to time clear air strikes occur. I have seen the occasional one travel a number of kms out of a storm cell and down to the ground

    This storm produced one of those ... I didn't capture the bolt on video unfortunately but have drawn on the pic the strike
    It continues a bit further off the left side of the image before hitting the ground

    upload_2016-12-10_8-50-9.png


    Dave
     
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