No description available.

Lightning electric field (E) and electric field derivative (dE/dt) signals have been recorded using sensors with 40 ns and 10 ns response times, respectively. Field propagation between the source and the recording antennas was entirely over salt water, so that distortions due to ground wave propagation were minimal below about 20 MHz. The fast-varying, initial portions of return stroke E fields have 10% to 90% risetimes which average 90 ± 40 ns. Peak dE/dt values range from 7 to 71 V/m/μs, with a mean and standard deviation of 33 ± 14 V/m/μs, when normalized to 100 km using an inverse distance dependence. The shapes of first and subsequent stroke fields are similar, but peak subsequent stroke dE/dts are larger than peak first stroke dE/dts in some flashes. The temporal structure of the fast varying fields produced by leader steps near the ground are very similar to return stroke fields. The mean maximum leader dE/dt, at 100 km, is 27 ± 9 V/m/μs. Large amplitude radiation fields produced by cloud discharge processes tend to be bipolar, with either positive or negative initial polarity and usually have several, fast, unipolar pulses superimposed on the initial half cycle. Cloud discharge fields with positive initial polarity usually precede cloud-to-ground flashes and produce a mean maximum dE/dt of 16 ± 8 V/m/μs. The field derivatives for all processes tend to be large when the amplitude of the associated fast field change is large. Estimates of lightning current derivatives, made using range normalized dE/dt measurements, average 155 ± 70 kA/μs, 135 ± 45 kA/μs, and 80 ± 40 kA/μs, for return strokes, leader steps, and cloud discharges, respectively, and a current wavefront velocity of 1 x 10⁸ m/s. These values are about 10 times larger than the maximum dI/dt recorded in strikes to instrumented towers. Lightning field amplitude spectra have been derived by Fourier analyzing dE/dt waveforms, and the spectral amplitudes decrease as 1/f² or faster with increasing frequency in the interval from about 6 to 20 MHz.

No description available.

Ten years (1997 - 2006) of summer (June, July, August) daytime (14 - 00 Z) Weather Surveillance Radar - 1988 Doppler data for Houston, TX were examined to determine the best radar-derived lightning forecasting predictors. Convective cells were tracked using a modified version of the Storm Cell Identification and Tracking (SCIT) algorithm and then correlated to cloud-to-ground lightning data from the National Lightning Detection Network (NLDN). Combinations of three radar reflectivity values (30, 35, and 40 dBZ) at four isothermal levels (-10, -15, -20, and updraft -10 degrees C) and a new radar-derived product, vertically integrated ice (VII), were used to optimize a radar-based lightning forecast algorithm. Forecasts were also delineated by range and the number of times a cell was identified and tracked by the modified SCIT algorithm. This study objectively analyzed 65,399 unique cells, and 1,028,510 to find the best lightning forecast criteria. Results show that using 30 dBZ at the -20 degrees C isotherm on cells within 75 km of the radar that have been tracked for at least 2 consecutive scan produces the best forecasts with a critical success index (CSI) of 0.71. The best VII predictor was 0.734 kg m-2 on cells within 75 km of the radar that have been tracked for at least 2 consecutive scans producing a CSI of 0.68. Results of this study further suggest that combining the radar reflectivity and VII methods can result in a more accurate lightning forecast than either method alone.

This study presents an overview of lightning formation and the correlations seen with soil moisture slope along with potential of tornadic thunderstorms. Three moisture classes (large, marginal, small) were created using soil moisture observed during three tornado outbreaks (June-02-1990, April-26-1994, May-13-1995) over the Midwest. Chi-square, Nearest Neighbor, and Point Density calculations were performed and suggest that lightning polarity/frequency shift between soil moisture classes at a = .01. Using lightning characteristics in the thunderstorm lifecycle, one is able to evaluate relative tornadogenesis areas within moisture classes some 8-10 hours in advance. Tornadogenesis points fell within expected areas indicating that borders between marginal and small moisture classes are approximate locations of stage change (mature to dissipation) of the thunderstorm lifecycle. Results are intended to be used as a tool that helps verify situations that are more likely to be tornadic when observing real-time lightning data from thunderstorms crossing significant soil moisture boundaries. / Department of Geography

Thesis (M.S.)--Ohio University, March, 2008. / Title from PDF t.p. Includes bibliographical references.

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

Thesis (Ph. D.)--University of Missouri-Columbia, 2008. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on June 15, 2009) Vita. Includes bibliographical references.

Thesis (M.S. in environmental science)--Washington State University, August 2009. / Title from PDF title page (viewed on Sept. 15, 2009). "School of Earth and Environmental Sciences." Includes bibliographical references (p. 54-56).

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