A1263235521kYaLc

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Improvements in the WWLLN network Growing
Detection Efficiencies for "Big Lightning" Events
Craig J. Rodger1, James B. Brundell2, Robert H.
Holzworth3, Erin H. Lay3, and Richard L. Dowden4
1. Physics Department, University of Otago,
Dunedin, New Zealand. 2. UltraMSK.com, Dunedin,
New Zealand. 3. Dept. Earth and Space Sciences,
University of Washington, Seattle, USA. 4. Low
Frequency Electromagnetic Research, Ltd, Dunedin,
New Zealand.
Craig J. Rodger Department of Physics University
of Otago Dunedin NEW ZEALAND
TLE Coupling Workshop 2008 Corte, France Session
1 (Thunderstorms Lightning) 1205-1225, 23 June
2008
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Multistation VLF WWLLN
A multi-station network operating at VLF is
currently being developed to provide global
realtime lightning locations. The aim is
sufficient receiving stations, advanced
processing algorithms and understanding of VLF
propagation to achieve the following
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• Realtime location of gt50 of cloud-ground
  flashes occurring anywhere on Earth.
• mean location accuracies lt10 km
• Locations to be accompanied by measurements of
  the lightning charge moment change associated
  with each discharge.

CURRENTLY WWLLN is developing. Improvements are
being made, and tests are being undertaken.
REALTIME means with only a few seconds (lt10s)
delay.
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Why WWLLN?
WWLLN World-Wide Lightning Location Network
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Why "Woolen" WWLLN?
New Zealand. Original home of the WWLLN, and also
once home of 70.3 million sheep in 1982 (now
decreased to 38.5 million StatsNZ, June 2007).
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2000First experimental tests used 3 VLF
receivers (Dunedin, Darwin, Perth), and hence was
ill conditioned. Confirmed potential of setup.
Late 2001-early 2002Operational network of 6
receivers stretching from Australasia to
Japan. June 200311 active stations plus Sao
Paulo (Brazil) mid-deployed. CURRENTLY 32
stations covering most longitude sectors (Jul.
2008) In addition, there are 8 stations expected
to join in the next 6 months.
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Station Hosts

• University of Otago
• Charles Darwin Univ.
• Griffith University
• Murdoch University
• Nat. Univ. of Singapore
• Osaka University
• IZMIRAN, Russian Academy of Sciences
• Eötvös Lorand University
• University of Washington
• Massachusetts Institute of Technology
• University of KwaZulu-Natal
• Brazilian Nat. Inst. for Space Research
• University of the South Pacific
• Los Alamos National Laboratory
• Univ. Nac. Autonoma de México
• Univ. de la Polynesie Francaise
• Tel Aviv University
• University of Sheffield
• Portugal Meteorological Inst.

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How does it work?
The lightning radiation produces radio wave
pulses (sferics) which propagate in the
waveguide formed by the Earth and the lower
ionosphere.
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All receiver VLF stations are based on university
campuses and research institutes. The antenna's
are generally mounted on ferro-concrete
buildings, which are adequate conductors at VLF
and thus remain at ground potential, shielding
the antenna from local man-made noise. The
vertical electric from strong lightning dominates
over power line noise, and so these stations do
not need to be at quiet sites to detect a lot of
lightning.
Dick Dowden on the roof of the Electrical
Engineering building, Osaka Univ.
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South Africa
New Zealand
Fifteen seconds of broadband VLF from WWLLN
E-field antennas located across the globe. Clear
lightning present everwhere!
Antarctica
Israel
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Regional variation in the OTD 5-year average
lightning activity
In order to see how WWLLN is doing, we test
against the OTD average pictures.
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Improving Global WWLLN Coverage
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Summary WWLLN locations produced by original
algorithm 2003 (Mar-Dec only) 11
stations 10.6 million locations 2004
19 stations 19.7 million locations 2005
23 stations 18.1 million locations 2006
28 stations 24.4 million locations 2007
30 stations 28.1 million locations
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Improving Global WWLLN Coverage by improving the
use of the observations. Upgraded Algorithm
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Increasing the number of stations has lead to
steady increases in the total number of high
quality lightning locations. From 19.7 million
in 2004 to 28.1 million in 2007. However, we are
only using some of the events sent back by each
station (3 per second). Increasing the reporting
rate lead to decreased locations as our algorithm
had more difficulty combining the timings to
produce quality locations. Improvements in the
algorithm were required! This has been a strong
focus of the WWLLN core team for the last 12
months or more.
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Improving Global WWLLN Coverage by Upgraded
Algorithm RESULTS of reprocessing same raw files
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28.1 million locations
45.7 million locations
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Estimate of Global Location Accuracy
Using Monte Carlo simulations we have found an
estimate of lightning location accuracy for the
April 2007 WWLLN station configuration, based on
2007 WWLLN observations and comparison with New
Zealand commercial lightning location data.
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Accuracy ranges over 4 km 400km. Global median
is 13km, global mean is 15 km. Promising, but
note the bad geometry in North Africa and Europe.
On average, 6.4 stations involved in the location
of each lightning.
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Global Detection Efficiency Estimates
Satellite observations indicate that the expected
mean geographic global annual average flash rate
is 445 flashes per second (Christian et al.,
JGR, 2003). What fraction of global lightning is
WWLLN reporting? fraction global
lightning 2004 19.7 million locations 1.4 20
05 18.1 million locations 1.3 2006 24.4
million locations 1.8 2007 28.1 million
locations 2.0 (orig.
algorithm) 2007 45.7 million locations
3.3 (new algorithm) Thats not so
good! However, we know WWLLN responds more to
high return stroke peak current lightning, from
CGs or ICs (Jacobson et al., J. Atmos. Ocean.
Tech, 2006). So contrast with NZLDN CGs.
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Detection Efficiency Peak Current?
We have previously used New Zealand Lightning
Detection Network data to show that the original
WWLLN algorithm detected 9-10 of NZLDN-reported
CGs with peak currents gt50kA.
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1 Oct 2003 31 Dec 2004
(Rodger et al., Fig. 5, Ann. Geophys., 2006)
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Detection Efficiency Peak Current?
Should consider the same like-with-like
comparison. So we look at the original
algorithm and compare with all NZLDN CG
observations from 2007.
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1 Jan - 31 Dec 2007
The algorithm detected 4 of all NZLDN CGs, with
big lightning is 9-10. Rather similar to 2004
despite improvements in the number of stations
worldwide.
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Detection Efficiency Peak Current?
Considering the NZLDN data from 2007, the new
algorithm provides DE improvements up to about
25-30 for gt50kA CGs. Almost a factor of three
improvement from the same set of raw observations!
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1 Jan - 31 Dec 2007
Very promising for linking to intense
thunderstorms! This new algorithm is currently
being used for the standard WWLLN output.
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Detection Eff. global estimate for big currents
WWLLN has a higher DE in the NZ sector than much
of the rest of the world, due to the high station
density in Asia and Oceania. The new WWLLN
algorithm reported 7 of all NZLDN CGs, about 2
times better than the global average. Hence on
a global level, it is likely that WWLLN now
reports 15 of all the worlds CGs with peak
currents gt50kA (i.e., one-half of the NZLDN
comparison for big lightning). We need to do
better. Can we? Additional stations will help,
and some are coming on-line. A steady growth in
stations lead to a improvement by a third, and
the new stations should improve coverage in the
Americas (if not Africa). However, there are
indications we can do still better with the
algorithm which determines the positions.
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Detection Efficiency Peak Current?
A very different location algorithm which we were
trialling achieved 50-60 detection efficiency
for gt50kA return stroke peak current CGs! It had
some unacceptable features which caused it to be
abandoned at this stage, but it shows what is
possible!
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1 Jan - 31 Dec 2007
Trial algorithm CRT
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Trial algorithm CRT
Unacceptable features unreal scatter and
suppression near equator
New algorithm in use
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Trial algorithm CRT
Unacceptable features quantised locations
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WWLLN Observations from Space
Even in its earliest days, WWLLN has played a
role in spacebased TLE-hunting experiments. Some
of the code currently used to display WWLLN data
on our webpage was rushed into operation to help
support the experiments undertaken onboard STS107.
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STS107 Marker. Arlington National Cemetery,
Washington DC.
http//wwlln.net/TOGA_network_global_maps.htm
Since then WWLLN data has been combined with
ISUAL Elves RHESSI TGFs.
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Currently WWLLN observations are supporting the
C/NOFS (Communications/Navigation Outage
Forecasting System) mission, which carries an
optical lightning sensor.
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Occurrence of Big Lightning from WWLLN
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On average Land WWLLN lightning peaks at 18LT,
oceanic lightning at 7UT.
Taken from Lay, Jacobson, Holzworth, Rodger, and
Dowden, Local Time Variation in Land/Ocean
Lightning Count Rates as Measured by the World
Wide Lightning Location Network, J. Geophys.
Res., 112, D13111, doi10.1029/2006JD007944, 2007.
Fig 8
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Occurrence of Big Lightning
Using the entire 2005 WWLLN data we examined the
changing diurnal occurrence of lightning.
Averaged over the entire globe, lightning peaks
at 18LT. However, this is not the same for each
continent. European lightning peaks 15LT, North
America at 19LT.
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Taken from Lay, Jacobson, Holzworth, Rodger, and
Dowden, Local Time Variation in Land/Ocean
Lightning Count Rates as Measured by the World
Wide Lightning Location Network, J. Geophys.
Res., 112, D13111, doi10.1029/2006JD007944, 2007.
Fig 8
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Big Lightning Atmospheric Impacts
The physical effects of big lightning is going
to be particularly important in the Americas
chimney region. BOTH lightning EMP impacts on the
atmosphere and particle precipitation fluxes are
strongly influenced by lightning peak currents.
Roughly 50 of WWLLN CGs occur in the nighttime
sector, hence 50 of lightning EMP will generate
elves (100 per minute). But note the strong
regional differences in nighttime big lightning!
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Taken from Lay, Jacobson, Holzworth, Rodger, and
Dowden, Local Time Variation in Land/Ocean
Lightning Count Rates as Measured by the World
Wide Lightning Location Network, J. Geophys.
Res., 112, D13111, doi10.1029/2006JD007944, 2007.
Fig 8
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Current products. http//webflash.ess.wa
shington.edu
On the VLF WWLLN website there are maps of
Updated every 10min and show lightning over the
last 40 minutes.
Global Lightning
Contact Prof. Bob Holzworth (Univ.
Washington) if you are interested in historic or
real time data.
There is also a contrast between the WWLLN
lightning events and satellite weather imagery
for Indian Ocean/Oceania, Europe/Africa and the
Americas regions!
bobholz_at_washington.edu
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Acknowledgements

• The results presented today are the result of
  measurements made at many varied institutions
  scattered across the Earth. Without the support
  of these institutions, WWLLN wouldnt be
  happening
• I would like to thank the workshop organizers for
  making this happen.
• I also want to acknowledge the funding support
  from the ASIM Topical Team funding through the
  European Space Agency. I really am grateful for
  this!

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Summary Conclusions

• Since 2003, increasing the number of WWLLN
  stations has lead to steady improvements in the
  total number of lightning locations, with strong
  improvements in global coverage. This has roughly
  doubled by the number of locations produced by
  the network.
• Recent improvements in the algorithm in which
  WWLLN observations are combined to produce
  lightning locations has also improved the
  detection efficiency of the network, by about
  two-thirds. More improvements are possible down
  this route, which just involve using the SAME
  data stream smarter.
• WWLLN only detects 3.3 of _all_ lightning in
  the globe (CGs and cloud flashes), but probably
  more like 15 of the global CGs gt50kA (and higher
  in some regions).
• WWLLN observations have already provided useful
  context for spacecraft missions, and are likely
  to provide more in the future.

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CAL workshop, Crete. Craig in the middle of his
presentation. June 2005.
Thankyou! Are there any questions?
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WWLLN lightning locations over-plotted on
Infra-red satellite images of Earth and clouds.
The red stars are active WWLLN receiver locations.
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Singapore antenna
Seattle antenna
Dunedin antenna