Lightning in NZ

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keithmeister
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Lightning in NZ

Unread post by keithmeister »

My friends and I are wondering why the incidence of Fork lightning (or cloud to ground lightning) is relatively rare in NZ, compared to somewhere like Australia. The majority of lightning here seems to be sheet lightning. Any facts or theories appreciated.
I'm thinking it's related to land mass
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Vertigo
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Re: Lightning in NZ

Unread post by Vertigo »

hi keith,

good question. but lets get the terminology right before we start, just to be as accurate as possible. sheet lightning is called intra-cloud lightning, or IC - it looks like the cloud is lighting up, but its still just a bolt inside it. fork lightning is when the bolt exits the cloud and hits the ground, and is called a cloud-to-ground strike, or CG.

nothing wrong with your terms btw, its just the the right terminology lends a hint as to the nature of the different forms.
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Vertigo
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Re: Lightning in NZ

Unread post by Vertigo »

IC and CG lightning have different radio signitures, which can be picked up on and plotted by lightning trackers, such as the Stormvue that a lot of us here use, so theorizing that they are formed in very different ways is no doubt plausible.

there are general attributes that are well known, however. both IC and CG come in positive and negative flavours, depending on the height that the lightning originates at (correct me if im wrong here, someone). IC tends to be produced when a storm is weaker, tho it can be observed in a storm of any strength. CG bolts are produced as a storm grows in strength, with negative strikes originating at lower levels, and positive strikes originating from the top of storms. therefore, to reach the ground, positive strikes tend to be more energetic - they have to be to even reach the ground. positive strikes can also loop back and re-enter the cloud near the bottom, where the charge is predominently negative.

so going by that, i would say that our thunderstorms tend to be much weaker than those observed overseas, and this is why we dont see as much CG lightning. this agrees with upper atmospheric data, which shows that we dont get nearly the levels of CAPE that Aus and the mid-west US get (our CAPE tends towards 1000J/kg, max, whereas the US can regularly get above 3000J/kg).
keithmeister
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Re: Lightning in NZ

Unread post by keithmeister »

Ok, so it's related to the energy present in the atmosphere during the storms? ( also, what is CAPE?)
Is this because of the general relative atmospheric pressure?
I guess I'm really wondering if it's because the large land masses of places like AUS and USA tend to lend more energy back to the atmosphere via heat etc, than NZ does?

All good stuff by the way. Just trying to get a definitive reason why.
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Vertigo
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Re: Lightning in NZ

Unread post by Vertigo »

CAPE is, if you want to get technical, the integral of the differential from observered ambient temp to parcel lapse rate, from the cloud base to the cloud top. for the rest of us, it is a measure of the energy density in a storm, measured in Joules per kilogram of air.

CAPE is measured computationally generally, but when you get familiar with reading upper atmosphere soundings (also known as skew-t diagrams), you can see the overall energy in the atmosphere at a glance. i cant really go into it in this thread, but there are websites around to learn how to read a skew-t diagram. the terminology is the hardest part, the actual diagrams are quite simple (they dont look it tho!).
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DT-NZ
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Re: Lightning in NZ

Unread post by DT-NZ »

Hi Vertigo :wave:

Appreciate your insights and thoughts ... ( thank you ) absorbing... taking it all in... learning... take care.
Lightning in NZ
The right terminology lends a hint as to the nature of the different forms.
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Re: Lightning in NZ

Unread post by TokWW »

Thanks Vertigo! So with high lapse rates, ie steeper temperature gradients than expected for rise in elevation, ie greater temperature extremes from below at ground level to above where a very cold air stream or jet-stream may exist, contrary to what is happening at or just above ground level, then you can get very volatile air masses rising and "boiling". The greater the temperature differences, then the greater the velocity and tumbling and energy involved. Hence with the air masses moving and static electricity being generated then we expect the strongest lightning is associated with the highest extremes in temperature differences and the greater heights that the Nimbus forms are created.

Hence, I surmise then that Keithmeister's assumption about land mass is probably correct, where you can get the greatest heating with large flat land masses and the high level airstreams do not mix so much with the mid level atmospheric clouds - the landforms are flatter and less inter cloud level mixing occurs. So the thunderstorms can gather more heigfht and more enerrgy and greater temperature differences. The perceived temperature lapse rate could be greater than that generated by elevation alone and ehence more velocity and turbulence...

All just postulated with an enquiring mind... Moisture content must come into this as well, increasing the air mass and "energy capacity" of the air and probably decreasing the path resistance for lightning to move?

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Dale
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Re: Lightning in NZ

Unread post by Dale »

Sort of related & reading through a couple of above posts.. this may come in very handy if you have a couple of spare hours to digest.. there is a lot of reading involved but it is a tool that my mentor & very close friend, Anthony Cornelius.. put together a few years back now.

Note: it has been more or less written for Australian conditions, but the principals are very much the same.

http://www.downunderchase.com/storminfo/stormguide/
AC's guide to forecasting your own thunderstorms (and potential.)
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Re: Lightning in NZ

Unread post by TokWW »

Thanks :)
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Re: Lightning in NZ

Unread post by Vertigo »

yes, i used that as reference while i was learning the trade :B
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Re: Lightning in NZ

Unread post by TokWW »

I didn't see any mention of forest fires (caused by lightning or otherwise) being a generator of lightning conditions, and also volcanoes, (perhaps I have not read far enough into it...) which I have seen evidence of both creating lightning. A good thorough read though - really enjoyed the links. I have to read through further yet, and I'll probably save the pdfs and file away and hand read. Thanks.
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Re: Lightning in NZ

Unread post by 03Stormchaser »

The number of cgs I saw last night is probably more than I have seen altogether since chasing storms in NZ... helps to be in bangkok though! lol
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Re: Lightning in NZ

Unread post by Lacertae »

Note: it has been more or less written for Australian conditions, but the principals are very much the same.

http://www.downunderchase.com/storminfo/stormguide/
AC's guide to forecasting your own thunderstorms (and potential.)
I would say the most important thing on this website is this chart :
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NZstorm
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Re: Lightning in NZ

Unread post by NZstorm »

I would change that chart to

60% Models
10% Instinct

The world of forecasting has changed dramatically in the last couple of decades, the performance of the weather forecasting models has greatly improved.
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Re: Lightning in NZ

Unread post by spwill »

60% instinct :lol: I think the day will come when it's near 100% models.
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Michael
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Re: Lightning in NZ

Unread post by Michael »

Means the other 30% simply looking out the window :-w
NZstorm wrote:I would change that chart to

60% Models
10% Instinct

The world of forecasting has changed dramatically in the last couple of decades, the performance of the weather forecasting models has greatly improved.
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Re: Lightning in NZ

Unread post by Weather Watcher »

Personally, as an operational thunderstorm forecaster, I would change that chart to...

80% Forecasts and models
19.9% Experience
0.1% Instinct
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Re: Lightning in NZ

Unread post by spwill »

That sounds about right Weather Watcher.
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Lacertae
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Re: Lightning in NZ

Unread post by Lacertae »

Sorry guys, I didn't precise that this chart is more for forecasting while chasing ... ;)
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Re: Lightning in NZ

Unread post by spwill »

Sorry guys, I didn't precise that this chart is more for forecasting while chasing ...
I still think instinct plays a very small part if any, experience helps alot.
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NZstorm
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Re: Lightning in NZ

Unread post by NZstorm »

I agree an operational weather forecaster shouldn't really be using instinct for forecasting but storm chasers certainly do use a bit of it in their forecasting. I do think the experience part of the equation would be reasonably high though. For example models can have a lot of difficulty with the mesoscale aspect of thunderstorm development but the experienced forecaster will possibly be better at resolving those issues. The mesoscale environment that led to the severe thunderstorms in the BOP on Monday were not detectable in the modelling. All the modelling was showing was an unstable environment over a wide area of the upper North Island.
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Re: Lightning in NZ

Unread post by spwill »

instinct for forecasting but storm chasers certainly do use a bit of it in their forecasting.
A personal thing I guess .
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Dale
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Re: Lightning in NZ

Unread post by Dale »

Lets not forget the guide was put together many years ago now... things have improved since then.
Not only model wise, but experience wise.. and this is the view of 1 person.
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Re: Lightning in NZ

Unread post by NZ Thunderstorm Soc »

Some 'sheet' lightning lashing away to the west tonight.
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Re: Lightning in NZ

Unread post by Razor »

Yep...been seeing the same John. Good display tonight. Between rugby games.
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