No description available.

The Maxwell current density (J(s)), electric field (E), and positive and negative air conductivities were measured simultaneously under several thunderstorms at the NASA Kennedy Space Center (KSC), Florida, during the summer of 1981. The components of J(m) include displacement current as well as field-dependent (J(s)) and convection (J(c)) currents. The measurements under active storms show that: (a) J(m) is usually dominated by displacement currents when E is close to zero, (b) J(m) is steady with time in the intervals between lightning discharges, (c) J(m) is usually not altered significantly by lightning, and (d) the average values of J(m) change slowly over time scales that are comparable to those required for storm development. Field-mill data have been used to derive estimates of the time-average J(m), ‘J(m), under a number of storms at KSC in the years 1976-1978 and 1981. Maps of ‘J(m) are consistent with the locations of radar echoes and lightning charges, and the patterns of ‘J(m) develop and change shape slowly with time. Maximum values of ‘J(m) for large storms are typically on the order of 10 to 15 na/m², and those for small storms are 2 to 4 na/m². Since J(m) is a solenoidal vector, area-integrals of the ‘J(m) maps (‘I) on the ground provided at least a lower limit to the total storm current aloft. Maximum values of ‘I for small convective storms are on the order of 0.1 to 0.5 A, and the maximum values for large storms are at least 3 to 5 times larger. Attempts to infer the location, magnitude, and geometry of the current sources aloft from the field-derived estimates of ‘J(m) have been hampered by a 10-20% variance in the values of ‘J(m). These errors prevent a unique characterization of the current sources aloft unless other data can be included in the analysis. Polar conductivities have been found to be highly variable in a thunderstorm environment, but the total conductivity often remains comparable to that found in fair weather. Conductivities derived from Maxwell current estimates of Jₑ vs. E are about an order of magnitude larger than the direct measurements; therefore, the Jₑ vs. E method of estimating σ may not be valued.

Thesis (Ph. D.)--University of Washington, 1997. / Vita. Includes bibliographical references (p. [94]-103).

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 104-111).

No description available.

The thesis is concerned with a study of the electrical engineering parameters of the lightning ground flash - i.e. the statistical distributions of peak current amplitudes, discharge current waveform characteristics, and flash striking distances - in the event of flashes to practical engineering structures. In view of its predominating frequency of occurrence in practical situations, the discharge of primary concern is the downward progressing and negatively charged ground flash. A central feature of this work is the establishment of a lightning research station (incorporating a 60 m instrumented mast) in the Transvaal highveld region of South Africa. The design of this station and the related measurement techniques are fully described. Preliminary results accumulated over a 6-year period of observation are presented, and include recordings obtained during direct strikes to the mast, as well as data from associated measurements of additional thunderstorm and lightning parameters. The latter studies include the use of closed circuit television video recordings, together with electrostatic field mills and lightning flash counters. Analysis of the resultant data serves to provide a comprehensive characterisation of the thunderstorm and lightning climatology in the region - on the basis of electrical activity. With only few exceptions, it is concluded that the characteristics of lightning observed in the. Transvaal region are generally consistent with the trends of data from other regions of the world. A unique aspect of the project is a study of lightning striking distances. An attempt to estimate these distances using bi-directional photography of flashes to the research mast is described, and several preliminary results are also presented - in conjunction with the associated measurements of discharge current amplitude. These results are compared with previously used relationships between striking distance and peak current. / Thesis (Ph.D.)-University of Natal, Durban, 1979.

Thesis (Ph. D.)--University of Washington, 2005. / Vita. Includes bibliographical references (p. 104-115).