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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Total lightning characteristics of ordinary convection

Motley, Shane Michael 02 June 2009 (has links)
Twenty-two isolated, non-severe, warm season thunderstorms (ordinary thunderstorms) were examined to test possible correlations between three-dimensional lightning flash characteristics and the complex evolution of the microphysical and kinematic processes involved in the electrical development of thunderstorms. Nine of the thunderstorm cases examined occurred within range of Vaisala Inc.'s Dallas-Fort Worth (DFW) Lightning Detection and Ranging (LDAR) network and the other thirteen cases occurred within range of the Texas A&M University Houston LDAR Network. Cloud-toground (CG) flash data were obtained from the National Lightning Detection Network (NLDN). The kinematic and microphysical properties of each convective cell were inferred from level II Weather Surveillance Radar 1988-Doppler data. Lightning properties were compared to radar reflectivity, Vertically Integrated Liquid, Severe Hail Index, and Vertically Integrated Ice (VII) (i.e. the measure of the precipitation ice water content in and above the mixed phase (-40°C < T < -10° C zone). In addition, total lightning (intra-cloud (IC) and CG) characteristics were compared against CG lightning characteristics to determine if total lightning data provide stronger correlations to convective intensity and state (i.e., developing, mature, dissipating) than CG lightning data alone. The results show that VII is well correlated to the total flash rate with r2 values of 0.45 and 0.81 for Houston and Dallas cases, respectively, whereas CG flashes show much weaker correlations to VII. The cases also follow the conventional model of lightning within ordinary storms with IC dominating over CG lightning in the initial stages of convective development. An average of 19 IC flashes occur before the first CG flash with an average lead-time between the first IC to the first CG of 12 minutes. Flash heights showed little correlation to VII, which is in disagreement with past studies suggesting that strong correlations exist between flash heights and storm intensity. Integration of the results from this study into an operational forecast setting could lead to improvements in the nowcasting of lightning threats using radar, numerical weather prediction via assimilation of total lightning data, and the nowcasting of severe weather and lightning hazards to aviation.
2

A system for measuring the electrical currents to the earth during thunderstorm conditions

Ward, Royden Carl, 1944- January 1970 (has links)
No description available.
3

THE ELECTRIC CURRENT DENSITIES BENEATH THUNDERSTORMS (CONDUCTIVITY).

BLAKESLEE, RICHARD JUDSON. January 1984 (has links)
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.
4

A modeling study of thunderstorm electrification and lightning flash rate /

Solomon, Robert, January 1997 (has links)
Thesis (Ph. D.)--University of Washington, 1997. / Vita. Includes bibliographical references (p. [94]-103).
5

How does lightning initiate and what controls lightning frequency? /

Schroeder, Vicki. January 2000 (has links)
Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 104-111).
6

Skill of synthetic superensemble hurricane forecasts for the Canadian Maritime Provinces

Szymczak, Heather Lynn. Krishnamurti, T. N. January 2004 (has links)
Thesis (M.S.)--Florida State University, 2004. / Advisor: Dr. T.N. Krishnamurti, Florida State University, College of Arts and Sciences, Dept. of Meteorology. Title and description from dissertation home page (Jan. 20, 2005). Includes bibliographical references.
7

Field experiment observations of a dryline and the associated clouds and precipitation

Daniel, Brown 06 1900 (has links)
The UNderstanding Severe Thunderstorms and Alberta Boundary Layer Experiment (UNSTABLE) in July 2008 was a field project to investigate the initiation of thunderstorms in southern Alberta. Special field observations included an enhanced surface network augmented with instrumented vehicles. Upper air observations were taken from four sites every two hours. This thesis focuses on the case study day of 17 July 2008 when a dryline formed parallel to the Rocky Mountains at 1030 MDT and persisted for up to nine hours. The vapour mixing ratio changed from 4.5 to 8.5 g/kg over 5 km. We documented the spatial and temporal distribution of cloud and precipitation relative to the dryline. Initially, extensive cloud formed over the dry air to the west of the dryline, while the capping inversion at 800 mb inhibited cloud formation in the moist air. In the afternoon, convection was triggered along the dryline and severe thunderstorms were observed.
8

The retreival of initial forecast fields from single Doppler observations of a supercell thunderstorm /

Weygandt, Stephen Scott. January 1998 (has links)
Thesis (Ph. D.)--University of Oklahoma, 1998. / Includes bibliographical references (leaves 247-257).
9

Air earth conduction current measurement by the direct method

Baugh, Raymond Chapman, 1933- January 1965 (has links)
No description available.
10

Field experiment observations of a dryline and the associated clouds and precipitation

Daniel, Brown Unknown Date
No description available.

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