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St. Elmo's Fire

Started by emerydc8, Sat, 4 Nov 2017 01:51

Jeroen Hoppenbrouwers


Hardy Heinlin

I think that article is about "St. Elmo's Fire", i.e. that steady "corona" at the tip of pointed objects.

torrence

Hi Hardy,

In addition to Holger's comments, it occurred to me that there are other things that distinguish the 'discharges' from lightning as modeled.  I've spent some time comparing Jon's discharge video with the default situ, which is a great example of lots of lightning, turbulence etc. in PSX.   The discharges look different because they are clearly on the windows, in the aircraft frame of reference and move when the aircraft does, while the lightning is 'outside' tied to the scenery frame of reference (i.e. they will be partially hidden behind window frame structures when banking etc.).  I don't know enough of all the magic you did with the native scenery vs inside the cockpit view to be sure, but could you do something with the 'discharges' that is just a series of momentary bright patterns *tied to the aircraft frame of reference".  If that could be done, along with Holger's points re altitude and low frequency of occurrence they wouldn't be mistaken easily for lightning.

Cheers,
Torrence
Cheers
Torrence

emerydc8

On the subject of lightening, this is a view out the left window as I was deviating around some weather. https://youtu.be/Eq7H1S_Ak88

Take a look at the amount of activity out there only 20-30 miles away and compare that to the lack of red returns on the ND (over CDS). I couldn't get any red returns to display no matter what tilt setting I used until I went to MAX on the gain. We were above most of this stuff, but I decided to deviate around the south side anyway.

This is a good example of why I don't like to leave the radar gain in AUTO or CAL (calibrated) and let it do its thing -- I don't trust it. This is especially true on our -400s. In the case of this video, you couldn't miss the lightening, but I've hit towering CBs at night at FL360 over India that had no lightening and weren't even painting on the radar while it was in AUTO/CAL. It was quite a surprise to go from glass-smooth air to severe turbulence in a split second. So, I'm a big fan of playing with the gain and tilt quite often during cruise if it's a dark night or if I suspect there could be weather ahead.

Hardy Heinlin

Nice shot, Jon :-)

Hi Torrence, yes I would refer to the aircraft frame, but still crop it at the window edges and would not display it for more than three time frames (minimum 40 ms). Within that short time the aircraft can't significantly change its attitude to demonstrate the different references. But the good point is that PSX only shows thunderbolts when the aircraft is below the CB, so they would never occur when those plasma effects only occur above the CB. A blueish color would also help to distinguish the effects. I'm thinking of these conditions:

aircraftAlt > CbTop
AND aircraftAlt < ( CbTop + 5000 )
AND lateralDistanceToCb < 50 nm
AND nighttime
AND randomizerSaysYeah


Cheers,

|-|ardy


jtsjc1

Quote from: emerydc8 on Tue, 14 Nov 2017 07:24
On the subject of lightening, this is a view out the left window as I was deviating around some weather. https://youtu.be/Eq7H1S_Ak88

Take a look at the amount of activity out there only 20-30 miles away and compare that to the lack of red returns on the ND (over CDS). I couldn't get any red returns to display no matter what tilt setting I used until I went to MAX on the gain. We were above most of this stuff, but I decided to deviate around the south side anyway.

This is a good example of why I don't like to leave the radar gain in AUTO or CAL (calibrated) and let it do its thing -- I don't trust it. This is especially true on our -400s. In the case of this video, you couldn't miss the lightening, but I've hit towering CBs at night at FL360 over India that had no lightening and weren't even painting on the radar while it was in AUTO/CAL. It was quite a surprise to go from glass-smooth air to severe turbulence in a split second. So, I'm a big fan of playing with the gain and tilt quite often during cruise if it's a dark night or if I suspect there could be weather ahead.
Very interesting thank you Jon.
Joe

cagarini

Another interesting source of info:

https://jpcvanheijst.com/blogs/2017/06/574544-st-elmo-s-fire-4-minute-read

But actually, even sandstorms, for instance in Africa, combined with sufficient convective activity, can bring particles to the higher levels of the troposphere, causing enough "static source" for this type of effect to take place, without the presence of TS.

Hardy Heinlin

They all call it St. Elmo's Fire. I think it is correct. The steady glow is certainly St. Elmo's Fire, and the occassional sparks are just another side effect of it, even though they are sparks and not a steady glow. St. Elmo's sparks, so to speak ...


|-|

United744

It's also caused by flying through precipitation, or cirrus. TS in vincinity just makes it more likely.

Hardy Heinlin

For reference, some other examples:

https://youtu.be/P1luqXNqC1c?t=2m23s

https://youtu.be/ZX7t4t_UPk8?t=1s

https://youtu.be/zyWX3VRsk38

https://youtu.be/qQiFBTDPhrs

https://youtu.be/NUYr0DPU3uM?t=12s

https://youtu.be/TxGPrlrgn34

https://youtu.be/Py5mkrrcLPU?t=16s

https://youtu.be/gILe7KAIAHY?t=39s


I now think St. Elmo's Fire is the purple glow on the aircraft nose, not the static discharge. In the above videos there is no purple glow, just static discharge.


|-|

Mark

Quote from: Hardy Heinlin on Sat, 18 Nov 2017 23:12
I now think St. Elmo's Fire is the purple glow on the aircraft nose, not the static discharge. In the above videos there is no purple glow, just static discharge.

Many years ago I did a lot of research on electrostatics, I would concur with your assessment that the static purple glow is St. Elmo's Fire (though I would just call it 'corona discharge'). Wikipedia shows a nice example.

It's a continuous effect; a glow that may have fine spark discharges inside it.
Your list of youtube videos are, like you said, just straightforward static discharges.

Edit: though I hesitate to assume Wikipedia is authoritative, it does state "The phenomenon known as St. Elmo's Fire was, and is, a common occurrence of corona discharge". Article here.

Hardy Heinlin

I'm changing my opinion on this every day :-) Today I think again that both the glow and the spark is St. Elmo's Fire. It's just a name of something that perhaps sailors invented some centuries ago; a name for a certain glow that is often accompanied by sparks. A debate about this name is actually a debate about an answer to the question: "What did those sailors see?" They probably saw both: glow and sparks.

It's similar to the question "the region up there between the two oceans, is that the USA or America?" It's not really America because America is the entire continent, not just a fraction of it. No, it's definetely America because it belongs to that continent. No, it's just the USA, not the entire continent. No, it's both.


}{ardy


cagarini

In Meteorology we cal all of those phenomena the same - St. Elmos fire is the common, non-scientific, designation though...



Hardy Heinlin

#33
Hi all,

for a random discharge flash I now set these conditions which are checked in an infinite loop:

IF ( aircraft is in volcanic ash OR ( any CB is within 77 nm
AND aircraft is above CB base
AND ( aircraft is between two cloud layers OR in cloud OR below ( cloudTop+2345 ft ) ) ) )
AND ( almost or total nighttime OR in cloud )
AND TAS > 342 kt
AND randomizer says yes
   

|-|

Hardy Heinlin

Well then ... when you see something rare like this, it's not a lightning strike in the scenery; it's a static discharge on the windshield :-)




|-|

Jeroen Hoppenbrouwers

Pretty!

Does it go towards your finger if you put it against the window?    :-D



Hoppie

Hardy Heinlin

It's so fast; you can't even hit the Pause key before it disappears :-)


|-|

emerydc8

Very nice, Hardy!

Jon

cagarini

I believe you found an excellent graphic representation. 

Thank you!

frumpy

Kind of you! It's a cool feature! :)