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299 results on '"Orville, Richard E."'

12. Radar reflectivity and lightning

Author

Toracinta, E. Richard, Mohr, Karen I., Zipser, Edward J., and Orville, Richard E.

Subjects
League City, Texas -- Environmental aspects, Lightning -- Research, Clouds -- Dynamics, Earth sciences
Abstract

This is the first part of a two part study. Part I compares radar data from the League City, Texas, WSR-88D and cloud-to-ground (CG) lightning data for a set of eight mesoscale convective systems (MCSs), which occur at various stages of development along the upper Texas gulf coast. Vertical profiles of radar reflectivity (VPRR) as well as plan views and vertical cross sections are constructed to characterize the structure and relative strength of each MCS. The VPRR are also compared with similar profiles from tropical oceanic MCSs. The data show that in all cases the majority of negative CG lightning flashes are located near high-reflectivity convective cores ([greater than]35 dBZ) in the mixed-phase region (0 [degrees] C [less than or equal to] T [greater than or equal to] -20 [degrees] C) Growing or mature MCSs typically had larger negative flash counts and higher percentages of negative lightning ([greater than]80%) associated with convective cores than MCSs at later stages of their life cycle. Comparison of the median VPRR for the various MCSs showed that although each case had high-reflectivity cores (45-55 dBZ) in the lowest 2-3 km, the more electrically active MCSs were characterized by smaller reflectivity lapse rates (decrease of reflectivity with height) in mixed-phase region than the cores in the remaining systems. Based on existing theories of charge separation, the observation of high negative flash counts coincident with convective cores having small reflectivity lapse rates in the mixed phase region is consistent with the presence of large ice particles aloft. Positive CG flashes were mostly located in low reflectivity (less than 30 dBZ near the - 10 [degrees] C level) stratiform regions, independent of MCS life cycle stage or VPRR type. Several cases with reports of large hail also had high positive flash densities associated with high reflectivity cores. Part II of this study compares 85-GHz brightness temperatures from the Special Sensor Microwave/Imager to lightning data for the same set of MCSs in Part I. Results from both parts of this study strongly suggest that the presence of large ice particles aloft is the common linkage between MCSs with lightning, with high radar reflectivity aloft, and large 85-GHz temperature depressions.

Published
1996

13. SSM/I brightness temperatures and lightning

Author

Mohr, Karen I., Toracinta, E. Richard, Zipser, Edward J., and Orville, Richard E.

Subjects
League City, Texas -- Environmental aspects, Lightning -- Research, Clouds -- Dynamics, Earth sciences
Abstract

This study examines simultaneous SSM/I and lightning data for a sample of nine mesoscale convective systems (MCS) near League City, Texas. Comparison of lightning files of varying sizes from [+ or -]2 to [+ or -]30 min revealed that the [+ or -]10-min interval representatively sampled electrical activity in mesoscale systems. The data strongly suggested that flash density was inversely correlated with 85-GHz brightness temperature. The highest negative flash densities corresponded to low ([less than or equal to]200 K) brightness temperatures. This relationship can be attributed to the scattering of upwelling 85-GHz radiation by graupel and hail, the same large particles believed to be necessary for charge separation. Variations were found depending on the sizes of an MCSs convective regions and its stage of development. The majority of positive flashes were located in the 210-250-K range. This brightness temperature range was comparable to the brightness temperature range of trailing stratiform regions and was consistent with observations of a higher percentage of positive lightning in stratiform regions. The results of both parts of this study implied that the pattern and magnitude of brightness temperature depressions and, by extension, the amount and distribution of lightning of an MCS was related to the presence of large ice particles in the mixed-phase region of that MCS.

Published
1996

15. Updates to analytical models

Author

Whitehead, James T., Chisolm, William A., Anderson, John G., Clayton, Roger, Elahi, Hamid, Eriksson, Andrew J., Grzybowski, Stanislaw, Hileman, Andrew R., Janischewskyj, Wasl, Longo, Vito J., Moser, Charles H., Mousa, Abdul M., Orville, Richard E., Parrish, Dee E., Rizk, Farouk A.M., and Renowden, Joseph R.

Subjects
Power lines -- Research, Lightning protection -- Research, Business, Computers, Electronics, Electronics and electrical industries
Abstract

The IEEE Simplified Method for computing lightning performance of overhead transmission lines was first described by Anderson. Since its publication, considerable experience has been obtained in the application of the method and in the testing of various component models. This paper describes application experience, sets out the theoretical basis for modifications and provides a framework for future advancements.

Published
1993

16. Simulation of the Universal-Time Diurnal Variation of the Global Electric Circuit Charging Rate

Author

Mackerras, David, Darveniza, Mat, Orville, Richard E, Williams, Earle R, and Goodman, Steven J

Subjects
Environment Pollution
Abstract

A global lightning model that includes diurnal and annual lightning variation, and total flash density versus latitude for each major land and ocean, has been used as the basis for simulating the global electric circuit charging rate. A particular objective has been to reconcile the difference in amplitude ratios [AR=(max-min)/mean] between global lightning diurnal variation (AR approximately equals 0.8) and the diurnal variation of typical atmospheric potential gradient curves (AR approximately equals 0.35). A constraint on the simulation is that the annual mean charging current should be about 1000 A. The global lightning model shows that negative ground flashes can contribute, at most, about 10-15% of the required current. For the purpose of the charging rate simulation, it was assumed that each ground flash contributes 5 C to the charging process. It was necessary to assume that all electrified clouds contribute to charging by means other than lightning, that the total flash rate can serve as an indirect indicator of the rate of charge transfer, and that oceanic electrified clouds contribute to charging even though they are relatively inefficient in producing lightning. It was also found necessary to add a diurnally invariant charging current component. By trial and error it was found that charging rate diurnal variation curves could be produced with amplitude ratios and general shapes similar to those of the potential gradient diurnal variation curves measured over ocean and arctic regions during voyages of the Carnegie Institute research vessels. The comparisons were made for the northern winter (Nov.-Feb.), the equinox (Mar., Apr., Sept., Oct.), the northern summer (May-Aug.), and the whole year.

Published
1999

18. The Lightning Discharge

Author

Orville, Richard E.

Abstract

Correspondence of Benjamin Franklin provides authenticity to a historical account of early work in the field of lightning. Present-day theories concerning the formation and propagation of lightning are expressed and photographic evidence provided. (CP)

Published
1976

25. editorial

Author

Hallgren, Richard E. and Orville, Richard E.

Published
1990

42. Cloud-to-ground lightning flash characteristics from June 1984 through May 1985

Author

Orville, Richard E, Weisman, Robert A, Pyle, Richard B, Henderson, Ronald W, and Orville, Richard E., Jr

Subjects
Meteorology And Climatology
Abstract

A magnetic direction-finding network for the detection of lightning cloud-to-ground strikes has been installed along the east coast of the United States. Time, location, flash polarity, stroke count, and peak signal amplitude are recorded in real time. The data were recorded from Maine to North Carolina and as far west as Ohio; analyses were restricted to flashes within 300 km of a direction finder. Measurements of peak signal strength have been obtained from 720,284 first return strokes lowering negative charge. The resulting distribution indicates that few negative strokes have peak currents exceeding 100 kA. Measurements have also been obtained of peak signal strength from 17,694 first return strokes lowering positive charge. These strokes have a median peak current of 45 kA, with some peak currents reaching 300-400 kA. The median peak signal strength and the peak current, double from summer to winter for both negative and positive first return strokes. The polarity of ground flashes is observed to be less than 5 percent positive throughout the summer and early fall, then increases to over 50 percent during the winter, and returns to less than 10 percent in early spring. The percent of positive flashes with one stroke is observed to be approximately 90 percent throughout the year. The percent of negative flashes with one stroke is observed to increase from 40 percent in the summer to approximately 80 percent in January, returning to less than 50 percent in the spring.

Published
1987

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