Lightning activity in thunderstorms

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jamie
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Lightning activity in thunderstorms

Unread post by jamie »

Thought id would make a new topic on this as we have been talking about it in another thread. It seems there are a few of us interested as to know why there is less activity in the updraft area and why some cells are more active than others. Thoughts???
re the lightning rotation thing..
it seems to me that mesocylones in the midwest did not have much lightning activity right under the meso....(but instead there was further away with the anvil), but when the meso's all joined up and straightlined in the evening into a bow echo and lost the rotation, then there was lots of lightning....thoughts?
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Re: Lightning activity in thunderstorms

Unread post by Weather Watcher »

I'll repeat what I said in the other thread here...

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I'm not an expert on lightning, and I don't really understand why some storms produce lots of lightning and others don't, but I do know that the location of lightning is often a function of updraft strength and vertical wind shear.

In general terms, during the charge separation process, the ice crystals become positively charged and are swept up to the higher levels of the storm while the water droplets become negatively charged and usually fall to the lower part of the storm. I suspect that in the strong updraft part of the storm that's associated with a mesocylcone, both the positively charged ice crystals and the negatively charged water droplets are being swept upwards, with the ice crystals being swept out into the anvil and then discharging (giving the lightning you observe near the anvil). Once the storms weaken (and form a line), the negatively charged water droplets are probably able to fall back down and discharge to the surface (giving all the lightning you observe near the convective line).

BTW, the distribution of positive and negative CG's are a function of vertical wind shear (especially in NZ). In low shear situations, where the storm is quite vertical, only the negatively charged water droplets discharge to the ground as the positively charge ice crystals in the upper parts of the storm can't "see" the ground and are unable to discharge. In storms which are tilted over from moderate or strong vertical wind shear, we see more positive CG's as the positively charged ice crystals can now "see" the ground and are able to discharge.

Interestingly we often see this across the Southern Alps in strong vertical wind shear situations with thunderstorms on the west coast, and spillover rain into Otago and Canterbury. In these situations, we have noticed that most of the CG's on the west coast are negatively charged (from the negatively charged water droplet forming rain) and most of the CG's east of the Alps are positively charged as they are coming from the positively charged ice crystals which have been swept up over the Alps at high levels (and eventually fall as spillover rain).

Hope that all makes sense.

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Re: Lightning activity in thunderstorms

Unread post by NZstorm »

Some very interesting points there Weather watcher.

One possible reason why supercell tornadoes sometime occur with no CG lightning is that tornadogensis occurs late in the lifecycle of a supercell and the tornado can be occurring in the decline stage of the storm. Once the tornado gets to the rope stage the mesocyclone is finished. If the environment allows, the storm can recycle and form a new meso nearby and the whole thing fires up again with CG's.

Brians point about straight line storms (squall lines) being particularly lightning active is interesting. I think in that case you have a highly organised and sustainable system where the inflows are being kept well clear of the outflows so strong updraughts are maintained. The late day linear storms in USA have awesome lightning shows.
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Re: Lightning activity in thunderstorms

Unread post by Weather Watcher »

NZstorm wrote: Brians point about straight line storms (squall lines) being particularly lightning active is interesting. I think in that case you have a highly organised and sustainable system where the inflows are being kept well clear of the outflows so strong updraughts are maintained. The late day linear storms in USA have awesome lightning shows.
Yes, I think you are correct there. Organised convective systems such as squall lines occur in moderate to strong vertical wind shear environments where the storms are tilted in the vertical which allows the updraft and downdraft to be separated, and the storm outflow interacts with the low-level environmental winds on the leading edge of the storm allowing new cells to develop.

I think the key here to the large amounts of lightning you observe is the vertical wind shear (tilted storms) which allows both the negatively charge raindrops and positively charged ice crystals to discharge to the ground, and the continual development of new convective cells on the leading edge of the squall line which keeps feeding the charge separation process.
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Re: Lightning activity in thunderstorms

Unread post by Manukau heads obs »

that makes sense :)
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Re: Lightning activity in thunderstorms

Unread post by drew »

Gidday,

Just wondering what CG's and IC's are.?

Being a big fan of electrical storms, I stop to watch them whenever I can, and we had a nice little rattler this morning.
I fired up the lightning radar and watched the event unfold, witnessing all the little CG and IC symbols poping up here and there, but as I am greener than the neighbors dairy runoff, I dont really understand what I am looking at other than the little dots showing lighting....

Thanks
Drew

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Re: Lightning activity in thunderstorms

Unread post by gllitz »

I believe the CG stands for "Cloud to Ground" strokes and IC stands for "Intra-Cloud" strokes...

EDIT: (Intra, not inter, sorry)
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Re: Lightning activity in thunderstorms

Unread post by Weather Watcher »

drew wrote:I fired up the lightning radar....
BTW, it's NOT a lightning radar. That is another incorrect term. It's a system which detects the electro-magnetic wave emitted by a lightning strike, that is it is more like your radio than a radar system. A radar transmits a pulse, then 'listens' for reflections coming back off an object like a plane, rain-drop, hailstone etc. Lightning detection systems do not do this.
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Re: Lightning activity in thunderstorms

Unread post by drew »

Weather Watcher wrote:
drew wrote:I fired up the lightning radar....
BTW, it's NOT a lightning radar. That is another incorrect term. It's a system which detects the electro-magnetic wave emitted by a lightning strike, that is it is more like your radio than a radar system. A radar transmits a pulse, then 'listens' for reflections coming back off an object like a plane, rain-drop, hailstone etc. Lightning detection systems do not do this.
Thanks for that.
I only called it a lightning radar due to the label on the web page.

http://www.weatherwatch.co.nz/content/lightning-radar

Thanks
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Re: Lightning activity in thunderstorms

Unread post by Nev »

Normally called simply 'Lightning Detectors'
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Re: Lightning activity in thunderstorms

Unread post by Weather Watcher »

drew wrote:
I only called it a lightning radar due to the label on the web page.

http://www.weatherwatch.co.nz/content/lightning-radar
Yes, the label on that web page is incorrect. As Nev says above, the better term is "Lightning Detectors".
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