Two Similar CG Lightning Flashes with Vastly Different Associated IC Activity

William H. Beasley1, Douglas M. Jordan2 and Stephanie A. Weiss1

1 University of Oklahoma2 University of Florida

Alternative Scholarly-Sounding Titles:

A Tale of Two Lightnings

or,

On the Varieties of Lightning Experience

Yesterday it became clear that in the context of NWP models, “lightning data” can mean a number of different things, including

NLDN or LLDN ground-strike data

LMA, LDAR or other VHF mapping data

Satellite optical data

WWLN ground-strike data

There was some discussion about what is to be gained by incorporation of lightning data of one kind or another in various models.

There was some discussion about the use of different types or aspects of lightning data.

Lightning data are being used in models as proxy for

Location (and timing?) of convection Strength of convection inferred from flash frequency, flash density, etc.

Lightning data are being used forInitializationNudging or adjustment,

typically by addition of latent heat or adjustment of stability?

There was some discussion about what constitutes a “flash”.

To help inform your judgment about the use of lightning data, I am going to show you that two CG flashes with apparently very similar characteristics can have vastly different associated IC activity that could make a difference in how the lightning is registered by different observing systems.

Further, I ask whether such differences could bear any relationship to differences in the parent storms?

In any case, clearly,

what you or I see

what an LMA/LDAR sees

what satellites see

What the WWLN sees

what the NALDN sees

what Alex Fierro saw from his balcony in Miami

can be quite different manifestations of lightning.

For some purposes, it may not matter what you call a flash.

W.H. Beasley

But, if you are going to use lightning characteristics such as flash frequency or flash density to modulate model parameters, then what constitutes a “flash”, as observed by any particular type of observing system, could matter.

To show you some cool high-speed images

To show you that CG flashes with very similar characteristics can have vastly different associated IC activity

To leave you with a sense of perspective on relation between, and relative scales of, CG and IC portions of lightning discharges

My Goals for Today

For two CG flashes I will show

Ordinary HDTV Video

NLDN data

High-Speed Images

VHF Source Locations

Radar Reflectivity

NLDN Ground-Strike points and Camera Location at

NWC

~ 4 km

Estimated heightof visible CG channel

HD video, 10:40:15 UT Flash

Ordinary HD camcorder

Two CG Flashes according to NLDN

One at 10:40:15.587 (to left of fov) probably a false positive CG

One of interest at 10:40:15.759

NLDN data @10:40:15

Flash Time lat lon Ipeak est

UTC deg deg kA

10:40:15.587 35.1159 -97.4094 +7*

10:40:15.759 35.1665 -97.4800 -6

*false positive CG

High Speed Video

Flash at 10:40:15.759951

Obtained with Photron SA1.1

10,000 frames per second

0.6665 seconds of dataStepped Leader in view for ~ 6 msContinuing current in view for ~300 ms~13 M-components in ~300 msHDTV video shows CC lasted >700 ms

10,000 fps video, 10:40:15 flash

VHF LMA data @ 10:40:15

Standard view using xlma

3d projection using Google Earth +

Animations using Google Earth +

Animation provided by Ken Cummins and Jean-Yves Lojou

10:40:15 Flash

Plan View

Projection of points

onto vertical E-W

plane

time history

Projection of points

onto vertical

N-S plane

40 km

25

km

Flash at 05/07/08 1040:15 UTC: XLMA interpretation

initial negative leader moves upward into positive charge negative breakdown propagates into the horizontal positive storm charge

region centered near 9.5 km as channel develops westward, it slopes downward to 6 km positive leader propagates horizontally through negative storm charge

centered near 4 km. negative leader to ground starts near 4 km and propagates horizontally for 6

km before turning toward the ground suggests localized region of positive storm charge near 3.5km just beneath the

main negative storm charge. Other flashes close in space and time to this flash also have negative leaders

moving through this positive storm charge however, most of these other flashes have leaders moving through only this positive

charge region and the negative charge region above it. negative leader to ground is unusual in this case because it seems to involve a third

charge region within the same flash. possible positive polarity breakdown moving along previously conducting negative

channels (from the westernmost end of the positive storm charge region back toward the flash initiation point) propagates close enough to the negative storm charge to cause a large enough electric field to initiate a new negative leader.

All VHF source locations10:40:15 flash

~ 5000 VHF source locations for the flash at 10:40:15, displayed in a 3d rendering.

Total duration of the flash is just under one second.

Total spatial extent is a significant fraction of 100 km.

Animated mapping of VHF sources

LMA data overview10:40:15.759951 flash

Nearly 5000 VHF source locations

Just under 1 second duration

No clear gap in activity between IC and CG portions of discharge

VHF sources during 6 ms of stepped leader in Photron FoV

Whole cc interval

10:40:15.759951 flash All LMA Points

HD video, 22:24:27 UT Flash

Ordinary HD camcorder

Two CG Flashes in fov

One at 22:24:27.669 of interest

Another High Speed Video

Trigger at 22:24:27.669368

Obtained with Photron SA1.1

10,000 frames per second

0.6665 seconds of dataStepped Leader duration ~ 2.3 msContinuing current duration ~12 msNo M-components

10,000 fps video, 22:24:27

VHF LMA data

22:24:27 Flash

Projection of pointsonto

vertical E-W plane

Plan View

time history

11 km

12

km

4 km

Similarities and Differences

Stepped Leaders, Branching Similar Upward-going leaders (attachment)

Similar Return-strokes Similar Continuing Currents Different

104015 flash had continuing current of extremely long duration (~700 ms) and numerous M components

222427 flash had continuing current of ~ 12 ms duration and no M components

How do the Meteorological Situations Compare

Look at Radar Images

Radar Only Radar with VHF SourcesRadar scan ~10:35 - 10:41

Radar and LMA data,10:40:15 flash, CAPPI at ~ 3 km

Radar Only Radar with VHF SourcesRadar scan ~22:23 - 22:29

Radar and LMA data, 22:24:29 flash, CAPPI at ~ 3 km

10:40:15 22:24:27

Radar and LMA data comparison

10:40:15 22:24:27

Radar and LMA data comparison

Observations and Comments

There were very few VHF radiation sources determined by the LMA to be co-located and contemporaneous with the stepped leader, return stroke and M components.

There were upward-going leaders before both return strokes In the last 100 s before rs approximately 50 meters length.

LMA data during photographically identified M-components suggests

discharge channel in cloud expands in at least two directions more or less simultaneously,

pretty much horizontally as suggested by Krehbiel (1979) and Proctor et al. (1988), but with some vertical extent also,

presumably this shows additional charge sources being tapped to keep cc going.

The continuing current for the 10:40:15 flash lasted more than 700 ms, exceeding the longest previously reported cc duration by about 200 ms (to the best of our knowledge).

The horizontal extent of the IC discharge during the extremely long cc is considerable, suggesting charge layer of considerable horizontal extent.

Comparison of radar images at time of the two flashes shows extensive stratiform* layer associated with long cc

in early morning flash more vertical structure indicative of convection

associated with short cc afternoon flash

*with apologies to Chuck Doswel

How would these two CG flashes appear to a satellite?

Do long continuing currents occur more often during stratiform storms?

Is large horizontal extent of charge layer necessary for long cc?

Is large horizontal extent of charge layer sufficient for long cc?

Is this possibly relevant to fire weather, since long ccs set fires?

Questions

Bill Rison, LMA dataDon MacGorman, LMA dataPhillip Bothwell, NLDN dataKen Cummins and Jean-Yves Lojou, 3d visualizationJulia Jordan, HD video support

This work has been supported in part by NSF grant ATM-072119 and in part by NASA EPSCoR grant NNX07AV48A/Oklahoma NASA Spacegrant

AcknowledgementsA Good Example of AGU Motto:

“Unselfish Cooperation in Research”

We gratefully acknowledge the valuable help of

Stay Tuned!