Two Similar CG Lightning Flashes with Vastly Different Associated IC Activity
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Transcript of Two Similar CG Lightning Flashes with Vastly Different Associated IC Activity
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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
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Alternative Scholarly-Sounding Titles:
A Tale of Two Lightnings
or,
On the Varieties of Lightning Experience
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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
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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.
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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?
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There was some discussion about what constitutes a “flash”.
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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.
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Further, I ask whether such differences could bear any relationship to differences in the parent storms?
In any case, clearly,
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what you or I see
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what an LMA/LDAR sees
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what satellites see
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What the WWLN sees
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what the NALDN sees
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what Alex Fierro saw from his balcony in Miami
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can be quite different manifestations of lightning.
For some purposes, it may not matter what you call a flash.
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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.
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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
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For two CG flashes I will show
Ordinary HDTV Video
NLDN data
High-Speed Images
VHF Source Locations
Radar Reflectivity
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NLDN Ground-Strike points and Camera Location at
NWC
~ 4 km
Estimated heightof visible CG channel
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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
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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
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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
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10,000 fps video, 10:40:15 flash
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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
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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
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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.
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All VHF source locations10:40:15 flash
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~ 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
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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
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VHF sources during 6 ms of stepped leader in Photron FoV
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Whole cc interval
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10:40:15.759951 flash All LMA Points
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HD video, 22:24:27 UT Flash
Ordinary HD camcorder
Two CG Flashes in fov
One at 22:24:27.669 of interest
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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
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10,000 fps video, 22:24:27
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VHF LMA data
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22:24:27 Flash
Projection of pointsonto
vertical E-W plane
Plan View
time history
11 km
12
km
4 km
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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
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How do the Meteorological Situations Compare
Look at Radar Images
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Radar Only Radar with VHF SourcesRadar scan ~10:35 - 10:41
Radar and LMA data,10:40:15 flash, CAPPI at ~ 3 km
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Radar Only Radar with VHF SourcesRadar scan ~22:23 - 22:29
Radar and LMA data, 22:24:29 flash, CAPPI at ~ 3 km
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10:40:15 22:24:27
Radar and LMA data comparison
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10:40:15 22:24:27
Radar and LMA data comparison
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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.
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There were upward-going leaders before both return strokes In the last 100 s before rs approximately 50 meters length.
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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,
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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).
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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
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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
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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
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Stay Tuned!