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Lightning detection over Houston , Texas is possible with the Lightning Detection
and Ranging (LDAR -II ) network and the National Lightning Detection Network
(NLDN ) . A comparison of the two datasets in conjunction with 37 isolated , ordinary
thunderstorms reveals a time separation of 3 .1 minutes between the first detected Very
High Frequency (VHF ) source (i .e . first intracloud discharge ) and the first cloud -toground
(CG ) lightning flash . This CG warning time is increased to 16 .1 minutes when
using the radar -defined criterion of when the 30 -dBZ contour first reaches the -10°C
isotherm level .
Several attempts were made to establish a similar characteristic that could be
used to forewarn the occurrence of the final CG in this storm type . Based on the average
radar characteristics during the last CG flash in each thunderstorm case , CG activity
comes to an end when the 45 -dBZ echo falls below the -10°C isotherm .
Detection efficiencies that remain slightly less than perfect for each network may
have allowed for some error when analyzing VHF sources and ground flashes for each convective case . Exhibiting this possible error , four cases actually recorded a greater
number of CG flashes than intracloud flashes , which is contrary to typical lightning
characteristics .
Future studies hope to increase the number of thunderstorm cases to analyze as
the LDAR network continues to observe more lightning events . Also , similar approaches
could be implemented in differing geographic regions of the country to observe if these
lightning characteristics vary depending on latitude , longitude , or climate . |
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