Skip to main content

GIGO and Lightning Formation (GIGO: Gammas In, Gammas Out)

Two recent lightning studies provide interesting insight into the formation of lightning and the terrestrial gamma flashes, (also known as dark lightning),  that sometimes accompany it[1][2][4].  While both studies make use of the radio pulses created during lightning formation they seem to differ in their explanations of how the radio pulses are created.

Lake Maracaibo from Wikipedia http://en.wikipedia.org/wiki/Catatumbo_lightning

First a little background on lightning formation.  The following great summary is from a recent post by +John Baez.[3]
"Lightning happens in stages. First, a streamer of electricity travels from one charged area to another, say, from a cloud to the ground, or from one layer within a cloud to another. This prompts a return stroke with the reverse charge to go in the opposite direction. The initial streamer electrified the air it moved through, creating a path of least resistance that allows the return stroke to carry a much greater current."

Both of the studies indicate that radio pulses associated with lightning are emitted from the thundercloud prior to the actual lightning, during the streamer formation mentioned above.  The two studies differ, however, in their attribution of the source of the radio pulses.  I'm a bit perplexed by the whole thing.  If there are any lightning experts that would like to chime in and clear everything up, that would be awesome!

Reference 1 details a study that was made possible by the coincidental detection of the same lightning flash over Lake Maracaibo, (picture 1), by two different satellites, (one of them was the satellite mentioned in [3]), as well as two different radio-based terrestrial lightning detectors.  By sorting out the signals from the various detectors, they were able to determine that the radio pulse took place shortly after the terrestrial gamma flash, (TGF), and they attribute the creation of the radio pulse to the gamma flash.
"We find that the TGF was produced deep in the thundercloud at the initial stage of an intracloud (IC) lightning before the leader reached the cloud top and extended horizontally. A strong radio pulse was produced by the TGF itself."[1]
The timing information agrees with the second study.  It's not made clear by the paper how the gamma flash created the radio pulse however.

The second study was based on lightning measurements made over Russia and Kazakhstan.  This project was concerned with measuring the same radio pulses mentioned in [1] in an effort to determine what initiates lightning creation.  Here's where we arrive at the GIGO model, (gammas in, gammas out).  The researchers present a model based on their data that indicates that the initial breakdown of the lightning conduction channel is caused by a cosmic gamma ray creating an ionization cascade.  They attribute the radio pulses, which they agree occur prior to the lightning, to the resulting high electron currents created by the ionization cascade.

Interestingly, the ionization cascade proposed by [2] for lightning formation is the same process used, (on a much smaller scale), in particle detectors known as wire chambers.  A high energy particle, (such as a cosmic ray), strikes an electron orbiting an atom of the gas filling the detector.  The electron is knocked out of its orbit ionizing the atom.  An electric field maintained in the detector accelerates the now free electron and it in turn ionizes additional gas atoms.  The electrons from these collisions ionize still more atoms and a cascade of electrons is formed which is detected by sensitive amplifiers built into the detector.

In particle detectors, if the cascade runs away and becomes too large it can damage the detector.  Special care is taken to make sure no small particles of dust or other pollutants are present in the detector as these can serve as nucleation points for further cascades. The Russian study indicates that small water and ice particles have the same effect in thunderclouds that dust has in wire chambers.  They serve as nucleation points that allow cosmic rays of lower energy than initially expected to create electron cascades that led to lightning strikes.

Thanks to  +Hans Havermann for pointing out the terrestrial gamma flash study!

All thoughts, comments, suggestions and clarifications are always welcome!

References:
1. Terrestrial Gamma Flash study
http://dx.doi.org/10.1002%2Fgrl.50466
Østgaard N., Gjesteland T., Carlson B.E., Collier A.B., Cummer S., Lu G. & Christian H.J. (2013). Simultaneous observations of optical lightning and terrestrial gamma ray flash from space, Geophysical Research Letters, n/a-n/a. DOI:

2.  Russian Lightning study
http://dx.doi.org/10.1103%2FPhysRevLett.110.185005
Gurevich A.V. & Karashtin A.N. (2013). Runaway Breakdown and Hydrometeors in Lightning Initiation, Physical Review Letters, 110 (18) DOI:

3.  +John Baez's post on dark lightning
https://plus.google.com/u/0/117663015413546257905/posts/NmQqg63S2bp

4. Open access synopsis of the Russian lightning study from the +American Physical Society
http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.110.185005

Comments

Popular posts from this blog

Cool Math Tricks: Deriving the Divergence, (Del or Nabla) into New (Cylindrical) Coordinate Systems

The following is a pretty lengthy procedure, but converting the divergence, (nabla, del) operator between coordinate systems comes up pretty often. While there are tables for converting between common coordinate systems, there seem to be fewer explanations of the procedure for deriving the conversion, so here goes!

What do we actually want?

To convert the Cartesian nabla



to the nabla for another coordinate system, say… cylindrical coordinates.



What we’ll need:

1. The Cartesian Nabla:



2. A set of equations relating the Cartesian coordinates to cylindrical coordinates:



3. A set of equations relating the Cartesian basis vectors to the basis vectors of the new coordinate system:



How to do it:

Use the chain rule for differentiation to convert the derivatives with respect to the Cartesian variables to derivatives with respect to the cylindrical variables.

The chain rule can be used to convert a differential operator in terms of one variable into a series of differential operators in terms of othe…

Lost Phone

We were incredibly lucky to have both been in university settings when our kids were born.  When No. 1 arrived, we were both still grad students.  Not long after No. 2 arrived, (about 10 days to be exact), mom-person defended her dissertation and gained the appellation prependage Dr. 

While there are lots of perks attendant to grad school, not the least of them phenomenal health insurance, that’s not the one that’s come to mind for me just now.  The one I’m most grateful for at the moment with respect to our kids was the opportunities for sheer independence.  Most days, we’d meet for lunch on the quad of whatever university we were hanging out at at the time, (physics research requires a bit of travel), to eat lunch.  During those lunches, the kids could crawl, toddle, or jog off into the distance.  There were no roads, and therefore no cars.  And, I realize now with a certain wistful bliss I had no knowledge of at the time, there were also very few people at hand that new what a baby…

Lab Book 2014_07_10 More NaI Characterization

Summary: Much more plunking around with the NaI detector and sources today.  A Pb shield was built to eliminate cosmic ray muons as well as potassium 40 radiation from the concreted building.  The spectra are much cleaner, but still don't have the count rates or distinctive peaks that are expected.
New to the experiment?  Scroll to the bottom to see background and get caught up.
Lab Book Threshold for the QVT is currently set at -1.49 volts.  Remember to divide this by 100 to get the actual threshold voltage. A new spectrum recording the lines of all three sources, Cs 137, Co 60, and Sr 90, was started at approximately 10:55. Took data for about an hour.
Started the Cs 137 only spectrum at about 11:55 AM

Here’s the no-source background from yesterday
In comparison, here’s the 3 source spectrum from this morning.

The three source spectrum shows peak structure not exhibited by the background alone. I forgot to take scope pictures of the Cs137 run. I do however, have the printout, and…