The Time Between First Radar Echoes and First VHF Lightning Radiation Source Locations as an Indicator of Eventual Storm Intensity
We found that for more than half of the storms analyzed the time between the first radar echo and the first indication of VHF source locations was ten minutes or less. We found that in general there was only a slight tendency towards higher echo tops when the time between radar echoes and VHF source locations was shorter. Furthermore, the difference between maximum tops and equilibrium level and between maximum tops and freezing level did not show any dependence on the time between first echoes and first VHF sources. Similarly, there was no discernible pattern of dependence of the average number of CG flashes per storm on the time between first echoes and first VHF source locations. We did find that when the time between the first radar echoes and the first VHF source locations was short, it was more likely that these storms would experience radar reflectivity increases of at least 5-10 dBZ following the first CG lightning flash and that storms reached their maximum in radar reflectivity faster if they became electrified more quickly. In the majority of cases analyzed (55 percent), the time between the first radar echo and the first CG lightning flash was between 5 and 15 minutes. Interestingly, however, in approximately 70% of the cases analyzed, the time between the first indication of VHF lightning radiation source points and the first CG lightning flash was between 0 and 5 minutes. This interval is not as long as indicated in some previous studies and so bears further examination. It may be that our criterion for first indication of VHF source points may have been too stringent. Finally, in general agreement with several previous studies, approximately 94 percent of the storms had base-scan radar reflectivity values of 38 dBZ or greater at the time of the first CG lightning flash. The results of this study, though encouraging, are indeed mixed, suggesting the need for further refinement with regard both to the early indications of radar and VHF radiation activity and to indicators of storm intensity.