Lightning in Supercells

[Andrew Khan]

Maybe someone can help me out here,

I am trying to figure out/learn what makes certain supercells have more lightning than other, while some have hardly any at all. I've seen numerous ones, that produce many CG's CC's, and just any sort of lightning. What is the most common out of a supercell, CG's? I am really interested in this, because I've seen one that produced so much, it was literally every hald of a second, continous lightning, and some don't even have it...it's confusing to me.

Thanks for any help.

 

[nickgrillo]

Originally posted by Andrew Khan
Maybe someone can help me out here,

I am trying to figure out/learn what makes certain supercells have more lightning than other, while some have hardly any at all. I've seen numerous ones, that produce many CG's CC's, and just any sort of lightning. What is the most common out of a supercell, CG's? I am really interested in this, because I've seen one that produced so much, it was literally every hald of a second, continous lightning, and some don't even have it...it's confusing to me.

Thanks for any help.

Often, the more intense an updraft is - the more lightning you'll get...

 

[Andrew Khan]

Why Nick? Is it because the constant strong updraft causes the electrons to move constantly, thus creating lightning?

 

[Mike Smith]

This is something that has baffled me for years.

The supercell that produced the Wichita-Andover tornado was one of the best documented storms ever. Yet, in all the video, I have never seen a CG nor have I heard thunder. The Lightning Detection Network showed exactly one CG in all of Sedgwick County with that storm. There was hail north of the tornado's path, so there was the multitude of precipitation types one would expect with a storm that produced a lot of lightning -- but this one did not.

Other tornado producing thunderstorms are profuse lightning producers (i.e., Mulvane tornado, June, 2004).

It appears that there are a multitude of parameters involved in generating cloud to ground lightning. We have a lightning prediction algorithm that works pretty well, but I'm always open to hearing additional thoughts/research to try to improve.

 

[Andrew Khan]

So precipitation helps to render lightning? It really was quite amazing, because it's so varying, and can change so easily. Other times you'll check the Lightning detection system, and see SO MANY strikes like in the past TX-OK Supercell, that had profuse lightning almost non-stop.

 

[Nic Wilson]

Here's a brief explanation of the physical causes behind lightning in a supercell.

1.) Strong updrafts are necessary to lift precipitation particles into the "mixed phase" region (typically -10 to -20 C) where ice crystals, graupel (soft hail particles) and supercooled water droplets (water that exists in temperatures below 0 C) can co-exist.

2.) The collision of riming graupel (graupel with a thin layer of water) and ice crystals exchanges charge -- this is known as the Non-inductive charging mechanism and is now widely accepted.

3.) Wind shear and the particles' differential sizes re-distribute these ice crystals and graupel to different parts of the storm building up a charge potential.

4.) Once the electrical breakdown threshold (~100,000 V/m) is reached, lightning occurs to "re-balance" the charge structure and environment of the supercell.

Climatology shows that ~ 70% of lightning are in-cloud flashes. In-cloud lightning almost always proceeds cloud-to-ground lightning. The initial charge separation usually occurs in this mixed phase region, atleast 4-6 km above ground level -- this promotes in-cloud flashes. Later in a supercell's lifecycle the updrafts weaken and the charge carrying precipitation particles are allowed to descend where they interact with charge potential differences at the surface -- leading to cloud-to-ground strikes.

The typical schematic of a supercell will see: Peak in in-cloud flashes ---> 5 to 15 min. later Peak in cloud-to-ground flashes ---> 5 to 15 min. later Peak in rainfall rate. Since a supercell is a self-sustaining entity it will go thru cycles of lightning activity and rainfall rates.

New sensing technology known as "Lightning Mapping Arrays" use a network of 7 to 12 sensors usually to passively receive the VHF (similar to television frequencies: 50-100 MHz) sources that the electrical breakdown associated with lightning emit. These can be mapped in 3D using time-of-arrival techniques or interferometry to pin-point the locations and paths of these in-cloud flashes, adding large amounts of data to the NLDN cloud-to-ground strike data which is extremely sparse in comparison.

Here is my paper I'm presenting at the AMS Radar Conf. later this month that shows ways in which "total lightning" data can be used in a complementary fashion with radar for use in forecasting and identification of storm features.

http://ams.confex.com/ams/32Rad11Meso/tech...paper_97291.htm