William L. Taylor

Lightning Rates Relative to Tornadic Storm Evolution on 22 May 1981

Abstract On 22 May 1981, we acquired lightning and Doppler radar data on two tornadic storms in Oklahoma. Cloud-to-ground lightning flash rates were measured with a magnetic direction-finder network, and total flash rates in the vicinity of the mesocyclone were measured with an L-band radar. In both storms, there was no clear relationship between tornado occurrence and ground flash rates of the storm as a whole, but the stroke rate of each storm was highest after it stopped producing tornadoes. For the second storm, we examined both intracloud and cloud-t-ground lightning rates relative to mesocyclone evolution, analyzing the region within 10 km of the mesocyclone core. Our analysis began during initial stages of the mesocyclone core associated with the fourth and strongest of five tornadoes in the storm and continued until all mesocyclone cores in the storm dissipated. During this period, intracloud lightning flash rates reached a peak of almost 14 min−1 approximately 10 min after the peak in cyclonic sh...

Explorer 45 observations of 1‐ to 30‐Hz magnetic fields near the plasmapause during magnetic storms

Observations have been made of <30-Hz magnetic fluctuations, some of which appear to be ion cyclotron waves, during initial, main, and recovery phases of magnetic storms. Such storm-related observable low-frequency events occur very infrequently, in only 10 instances in more than 2000 hours of data, including approximately 100 passes through storm time ring currents. All events were observed while the satellite was near the plasmapause and in the proton ring current. The wave amplitudes were typically 1 γ and as large as 5 γ in the frequency range from 1 to 3 Hz, with lower amplitudes in the 3- to 30-Hz range. On the basis of the spectral shape and intensity of the fluctuations the waves were presumed to be primarily ion cyclotron waves. Reasonable agreement was found between calculated ring current proton lifetimes while the protons were under the influence of ion cyclotron waves and observed proton lifetimes during parts of the December 1971 and August 1972 magnetic storms. These observations during times when the ring current and plasmasphere were close and often overlapping do not prove that the waves were generated by the ion cyclotron instability or that the ion cyclotron waves were necessarily responsible for proton ring current loss. The observations do suggest that ion cyclotron waves are unstable in such cases and that proton lifetimes are consistent with loss from ion cyclotron turbulence. Further theoretical (ion cyclotron wave growth limits) and observational (proton energy and pitch angle distribution changes during these or similar events) studies are required before the role of the ion cyclotron instability in ring current dynamics can be completely determined.