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LiGhtninG
does not report the locations of these strokes at the exact
location of the Brixton Tower due to the MDF and TOA errors
that are involved in the stroke location methods as previously
mentioned.
The data for the lightning flash is shown graphically in figure
3. A distinction is made between strokes to the Brixton Tower
(indicated by the inverted triangles) and strokes that nearby
(indicated by the solid circles). The figure then shows the
distance from the Brixton Tower that each stroke was reported
have occurred at as well as how many sensors detected each
stroke. Strokes to the tower (inverted triangles) that were
detected by many sensors are reported to have occurred near
the tower and this is indicated in Region A (blue area). Strokes
that were not to the tower (solid circles) but were still detected
by many sensors are reported to be far from the tower as seen
in Region B (white area). Strokes detected by few sensors,
found in the orange area, Region C, are both near and far from
the tower regardless of whether they were to the tower or not.
conclusion
These are observations that need to be considered when
information provided by LDNs is to be used as evidence for
lightning activity. If the location of an event involving damage
or loss of life is known but the time at which the event occurred
is not, care must be taken deciding if a lightning flash caused
the damage based on LDN data. The LDN may have reported
a lightning stroke near the location of the event. If this stroke
38 | wattnow | may 2012
continues from pg 36
There are two measures of how
effectively an LDN is operating:
Detection Efficiency and
Location Accuracy.
Figure 3. Lightning data from SALDN for the Johannesburg region,
10 May 2010. The distance between the location the SALDN reported
strokes to have occurred and the location of the Brixton is compared
with the number of sensors that detected the stroke.
was only detected by a few sensors, it is likely that there may
be an error in the reported location. Strokes detected by
many sensors are more likely to have their location reported
accurately.
references
• Blumenthal,R.,Jandrell,I.R.,Anderson,R.B. andTrengrove,
E., “Recent lightning research in South Africa with a special
focus on keraunopathology,” 16th International Symposium
on High Voltage, vol. K-1, pp. 1 6, 2009
• Rakov, V.A. and Uman, M.A., “Lightning Physics and
Effects”, Cambridge University Press, The Edinburgh
Building, Cambridge CB2 2RU, England, 2003
• Mata, C.T., Mata, A.G., Rakov, V.A., Nag, A. and Saul, J.,
“Evaluation of the Performance Characteristics of CGLSS
II and U.S.NLDN using Ground-Truth Data from Launch
Complex 39B, Kennedy Space Center, Florida,” 22nd
International Lightning Detection Conference and 4th
Lightning Meteorology Conference, Broomfield, Colorado,
USA, April 2012
• Jerauld, J., Rakov, V.A., Uman, M.A., Rambo, K.J., Jordan,
D.M., "An Evaluation of the Performance Characteristics
of the U.S. National Lightning Detection in Florida using
Rocket-Triggered Lightning", Journal of Geophysical
Research, vol.110, D19106, 2005