Lightning oscillations

[jimlucke]

What is the cause of the "W" shape in my lightning signal? Is it real or is there a resonance in my antenna? Sometimes there are more cycles but the spacing is consistent, around 10 kHz. I don't see this curve in any articles about lightning physics, though some show oscillations but very rough.


I have seen this curve in other nearby station's data but I do not know their antenna setup. I have 4 turns on a 1-meter X-frame, no transformer, directly connected to the external H-amplifier. Turn spacing is about 2 mm.


Because of bad noise I have the low-pass filter installed, but I have seen the same curves without the filter during lucky stretches when the noise stops.


All the strikes are 2500 km or more from me, so maybe the curve is explained by different frequencies taking different paths. I will have to wait until summer to see the shape of closer strikes.

I will try to attach an image from lightningmaps.org


Jim Lucke
Saimaanharju Finland

[RichoAnd]

I is (should bee?) well known, than long distance lightning signals are following the ionosphere waveguide, and the dominent frequency in this waveguide is 10-11kHz.
What you see is exactly this phenomenon :-)
For the same reason, the receivers made for just very long distance lightning, are often tuned to that frequency.
Tuning provides shifts in the signal path (delay), and gives inaccuracy in the position fixing.
This delay we do not want - and that's why our receivers are a little more complicated than you would otherwise see.
What wave guide does is a physical phenomenon which we can not do anything about.
Well - because of this phenomenon, we can "see" far but not place determine as accurately as nearby lightning.

https://en.wikipedia.org/wiki/Earth%E2%8..._waveguide

/Richo

P.S. By the way - the signal you are viewing is often called "a Mexican hat"

[jimlucke]

>the dominent frequency in this waveguide is 10-11kHz.

Very interesting, and complicated, like nature always is.
I have to use the LP filter because the noise at 65 and 80 kHz makes my station nearly unusable. I know it introduces a delay also.
Is there any reason to otherwise keep the pass band as high as possible? I have other noises at 20 kHz but not too bad, but I kept lowering the cut-off even down to 14 kHz. That is why my wave looks so smooth.
I did notice a few weeks ago that close lightning from the Norway coast looked different. Now it makes sense that the wave is altered on the way to Finland from Pakistan for example.
Jim

[cutty]

>the dominent frequency in this waveguide is 10-11kHz.

Very interesting, and complicated, like nature always is.
I have to use the LP filter because the noise at 65 and 80 kHz makes my station nearly unusable. I know it introduces a delay also.
Is there any reason to otherwise keep the pass band as high as possible? I have other noises at 20 kHz but not too bad, but I kept lowering the cut-off even down to 14 kHz. That is why my wave looks so smooth.
I did notice a few weeks ago that close lightning from the Norway coast looked different. Now it makes sense that the wave is altered on the way to Finland from Pakistan for example.
Jim

 

Jim, a couple of years ago, I started a 'primer' document... never pursued it, but I'll share it here, attached...
It tries to be very basic...   I approached it in the "BONES' rationalization, as: "I'm an Operator, Jim! Not a Physicist"...

It speaks of the "Ground Wave" and the "Sky Wave" for simplicity, but there are actually 3 components of interest,...
the "Ground Wave" from a source follows terrain, and depending on geology, geography, etc, can travel sometimes  a bit further than its associated "Space Wave" (Don't confuse with "Sky Wave"... they're different).

The 'second' component of the Ground Wave terminology is  a direct signal straight line from Source called the "Space Wave"... directly in the 'airspace" between the source and the detector. Reception depends on altitude, among other things, of the source, and receiving antenna...
so when the 'horizon' is reached, it's a rare part of the "Space Wave" signal that reaches you, although the 'ground wave component' may be available at a bit more distance.The effective reception distance from source for ground wave components is maybe 80km / 50mi/.
The only expected delay is pure travel time at the speed of light, from the source, + any delays in antennas or receiver processing.

Beyond that distance limit for "Best" groundwave reception, we're detecting 'skywaves'... those that reflect between the earth and the ionosphere,... and here this can be la-la land in terms of frequency spectrum of the impulse, distortion,Time of Arrival, etc  Most affected portions of the impulse are the higher frequencies, which don't bounce as well, but the lower frequencies can 'ring' and bounce through the waveguide. The time the signal reaches an antenna depends on the number of bounces, therefore greater distance traveled. And that 'bounce' depends on terrain, height of various levels of the ionosphere which fluctuate both in particle/charge content and it's altitude especially from day to night. This is called the "Earth-Ionospher Waveguide".
And both the Earth side and Ionosphere side of the waveguide only tend to bounce the 'lower' frequency components....

So, as Richo mentioned, we're getting most energy for those skywaves at around 10-11 kHz (There is at least one researcher who after years of collecting data, suggests the 'median' is right at 13 kHz) Whatever.

So as illustrated in your signal image, (and in one of the diagrams in the attached) you have a great 'Mexican hat' caused by 'skywave' capture
... which include little or NONE of the precharge, initial charging and discharge stroke frequencies (Higher), but only multiple 'skywave' signals.... of much lower frequencies.

One way to tell,


You might note that nearby Low Frequency sources, specifically those that generate a 'radio' signal are consistent in
cycle repetition, and don't typically have the 'delay' accumulation noted in sferic impulses at distance.

So... receiving low end frequencies only, if you have to filter, ain't bad... you're still 'detecting' them .!  Nearby cells have
a much stronger 'higher frequency' energy component, and there are uses for that higher frequency data... Blitzortung
has dreams for that data down the road, but none of that matters if the network cannot detect a signal.  So, as a
'single' station might have to operate low end, you still detect, and enable location... The other stations without the issues in
the higher frequencies can contribute that additional data... they might not be able to unless you assist with location! 
It's a TEAM Effort!

OH... by the way... the server knows how much time delay is designed into your system, the expected time delays of the filters,
antenna type, etc.. if you've configured correctly, and entered the correct data on your station page at BT...
...so it knows what to expect,and it takes all that into account when processing. So if folks diddle around with 'redesign', strange antennas, other stuff, it can mess things up.

Cheers!
Mike

[jimlucke]

> a couple of years ago, I started a 'primer' document..

Wow, a very extensive reply. I still haven't read it all.

I had been wondering if my lightning data was real. Yesterday I got a pulse from Kenya, 7300 km distant. I looked at the stroke data and it seems to be real, since the wave passed nearby stations within milliseconds of my timing.

I will have a chance to see sky waves I suppose next summer. In the meantime I have hundreds of sombreros from Italy and Turkey.

Your primer should be more widely known on this site. Thanks for all the info.



Jim

[pasense]

The primer is a very good start but should be extended. The signals you are showing, are they magnetic (B) signals or electric (E) signals? The reason is, I am interested in knowing the polarity of flashes and also  their strength (in kA). Currently, this information is not extracted, but are there plans to do so in the (near?) future? With this information, this network would be a really good research instrument.

[cutty]

Jim, if you're wearing 'sombreros' (Mexican Hats), you're getting skywaves... generally it's a 'skywave' if it's further than about 80lm /50mi. One issue with detecting Skywaves, is the time of group arrival Zero Crossings are also distorted, So in addition to 'built in" distance and timing location deviation, the TOGA iterations also won't be as accurate... so location accuracy suffers. (One reason so many primary detectors are used, along with another 6-8 secondaries, for computation...

Pasense
The Primer might get extended... but there is not much than can be added that isn't already referenced somewhere,... being a hobby... and certainly no extensions should be made without input and approval of the developers, simply because this is built around a specialized, hobby concept... though it certainly ranks with most any commercial system... beyond the basics, it's pretty much up to each of us to experiment, study, etc.  especially troubleshooting and 'noise'..;. those can't often be done long distance... each operator has to figure it out.

About polarity and strength, type of stroke ... Both Red and Blue theoretically, by design, as far as we know, CAN supply data for polarity, and stroke type (CG, IC, CC) ... however, strength of a strike in any system would always be a 'best guess'... as with altitude. altitude is a real dream world... almost impossible...

For polarity, the BLUE virtually has that built in... the third channel H field can be used with the third antenna oriented to detect the horizontally polarized H impulse..eg, ferrites are normally mounted horizontal, responding to the more common Vertically Polarized impulses... the third antenna could mount Vertically, for detection of NEARBY horizontally polarized strokes. Experimentation encouraged, but the system isn't yet set up for it, because...
.. a big IF.... everybody operated with the same antennas, similar configuration,for starters, the polarity algorithms etc might already be implemented along with betas for CC, IC types.. Another drawback is Egon, Richo, and Tobi have full time vocations and lives outside Blitzortung, so are limited at many times on their available time and energy for development and implementation. 

The illustrated signals you asked  about are H channel 1 signals from my system red, The E channel signals would be similar, with some phasing differences.  Note that E channel is really designed  Vertically polarized sigs  <800km or so not distant signals.  The goal was to use that in some of the advanced stroke parameters. Many operators are using that field for distant, so there is a big variance in data assumptions.

Speculation: The term "H field" for the magnetic portion is probably used so everything references to "vacuum", and allowing for antenna type differences... also the math computation may be simpler overall, rather than trying to derive everything necessary for thousands of stations, that would be required for "B"... then you've got the 'bound' fields,, "M", and remembering that changes in B produce changes in E and vice versa... and... and.. so, we just use H for discussion simplicity.... sort of like NOT referring to "Tuning up my station"... we don't wont any 'tuning'... we 'optimize..

[jimlucke]

Jim, if you're wearing 'sombreros' (Mexican Hats), you're getting skywaves... generally it's a 'skywave' if it's further than about 80lm /50mi.

I guess conditions are good for sky waves, since I am 2400 km from the Meditterranean storms. It's been 50 years since I had my ham radio rig but I remember sometimes the band is 'dead' and at other times the band was crowded with stations from all over. In fact I usually don't get good lightning signals from Italy because of the orientation of my loop, but the past few days has been busy. Then there was that signal from Kenya.
Jim

[allsorts]

Cutty: Excellent post. I've read it, thought I followed it, but now find I need to read it again

Jimlucke: Don't be surprised at receiving the Mediterranean storms, the system is designed for distant rather than close reception. A 1 us timing "error" is less significant at 2000km than it is at 200 km. I've also seen quite a number of signals from the west coast of Africa, 4000 miles (6500 km) or so away. And for a goodly number of those my stations signal data was used in the calculation, it was that that really convinced me that the station really had picked up those signals.