Clements, Nathan Chase (2007-12). The warning time for cloud-to-ground lightning in isolated, ordinary thunderstorms over Houston, Texas. Master's Thesis. Thesis uri icon

abstract

  • 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.
  • 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.

publication date

  • December 2007