High Time Resolution Lightning Mapping Lightning Mapping Observations of a Small Thunderstorm during STEPS

During the 2000 STEPS (Severe Thunderstorm Electrification and Precipitation Study) program, the New Mexico Tech Lightning Mapping Array (LMA) was operated in high time resolution mode [Rison et al., 2000] for several days. On July 11 a small thunderstorm formed over the northern part of the LMA network while the LMA was in this mode. The lightning mapping observations show that the electrical structure of the thunderstorm changed significantly during its lifetime. The electrical development of the storm as inferred from the lightning mapping observations will be presented. In high time resolution mode the LMA records the time of the strongest VHF radiation received in 10 μ s windows (compared to 100~μ s windows in normal time resolution mode). In high time resolution mode the LMA can produce significantly more detailed images of continuous radiation processes (such as stepped leaders, dart leaders and K-changes). Cloud-to-ground discharges examined in the July 11 storm show significant branching in stepped leaders, and there is sufficient detail in stepped and dart leaders and K-changes that good velocities for relatively fast leader processes (10⁷ m/s) can be determined. [1ex] Rison, W., P. Krehbiel, R. Thomas, T. Hamlin, and J. Harlin, A Time-of-Arrival Lightning Mapping System with High Time Resolution, Abstract A52C-01, Fall Ann. Mtg. Amer. Geophys. Union, EOS, 81, p. F47, 2000.