"An attempt is made to examine the credibility and explore the implications of the reports of convective clouds to extreme heights which have been indicated by radar in recent years. The extreme cases have not been verified by independent observations and it is shown that inherent limitations in radar observations of convective cloud heights are such as to raise serious doubts in regard to the accuracy of many of the extreme echo heights which have been reported"--Abstract. / Typescript. / "Scientific report to the U.S. Navy Weather Research Facility, Norfolk, Virginia, under contract N189-50775A." / "15 April 1962." / Includes bibliographical references (leaves 32-34).

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This study is mainly concentrated on examining the positive cloud-to-ground lightning activity associated with Mesoscale Convective Systems. Six MCS events which occurred during the O.K. PRE-STORM program in 1985 are studied. Data indicating the location and polarity of the cloud-to-ground lightning flashes from a lightning location network are analyzed in conjunction with the low-level echo patterns as obtained from radar. Spatial and temporal characteristics of positive cloud-to-ground flashes are identified from the data analysis. For all cases examined, positive cloud-to-ground flashes were found most commonly in the stratiform regions of the MCSs examined, and their frequency tended to peak during the later stages of the storm lifecycle. Two mechanisms responsible for the occurrence of positive cloud-to-ground lightning flashes with the above spatial and temporal characteristics are discussed. Based on the laboratory results, a 1-D charge generation model is developed. The model results show that in-situ charging is unlikely to be the dominant mechanism for charge generation in the stratiform region under normal atmospheric conditions. Sensitivity studies show, however, that in-situ charging processes strongly depend upon the liquid water, graupel and snow contents in the cloud. Under favorable atmospheric conditions, in-situ charging may lead to a significant charge generation. Hence, we cannot completely dismiss in-situ charging mechanism. Analysis of wind fields from dual-Doppler radar in combination with vertical profile of electric fields indicates that charge advection from the convective region to the stratiform region of MCSs may be a potential mechanism responsible for the occurrence of positive cloud-to-ground lightning flashes in the stratiform region. / Graduation date: 1989

Mesoscale convective vortices (MCVs), which typically form within the stratiform rain of some mesoscale convective systems (MCSs), may persist for days, often regenerating convection daily. Long-lived MCVs can produce as much precipitation as a landfalling hurricane and lead to catastrophic flooding. The number of studies using multi-Doppler radar observations for validation of the kinematics, or three-dimensional (3-D) wind structure, of MCV genesis is limited. For this study, the Oklahoma City (KTLX) and Tulsa, Oklahoma (KINX) Weather Surveillance Radar – 1988 Doppler (WSR-88D) were used to examine the genesis of a long-lived MCV from 0000 to 0300 UTC on 11 June 2003. Traditional dual-Doppler techniques were used to determine the 3-D wind field. To relate MCV genesis within the associated larger MCS, time series of convective and stratiform precipitation, divergence, vertical vorticity, and vertical velocity were created for multiple levels within the MCS. The role of vertical vorticity generated in the convective region in MCV development was determined using vertical profiles of the terms in the vorticity tendency equation at 15 minute temporal resolution during the three hour period of investigation. The results of this study provide a detailed three hour examination for the initiation and early evolution of a long-lived MCV and can provide model validation of MCV generation.

Mesoscale convective vortices (MCVs), which typically form within the stratiform rain of some mesoscale convective systems (MCSs), may persist for days, often regenerating convection daily. Long-lived MCVs can produce as much precipitation as a landfalling hurricane and lead to catastrophic flooding. The number of studies using multi-Doppler radar observations for validation of the kinematics, or three-dimensional (3-D) wind structure, of MCV genesis is limited. For this study, the Oklahoma City (KTLX) and Tulsa, Oklahoma (KINX) Weather Surveillance Radar – 1988 Doppler (WSR-88D) were used to examine the genesis of a long-lived MCV from 0000 to 0300 UTC on 11 June 2003. Traditional dual-Doppler techniques were used to determine the 3-D wind field. To relate MCV genesis within the associated larger MCS, time series of convective and stratiform precipitation, divergence, vertical vorticity, and vertical velocity were created for multiple levels within the MCS. The role of vertical vorticity generated in the convective region in MCV development was determined using vertical profiles of the terms in the vorticity tendency equation at 15 minute temporal resolution during the three hour period of investigation. The results of this study provide a detailed three hour examination for the initiation and early evolution of a long-lived MCV and can provide model validation of MCV generation.

Thesis (M. Sc.)--University of Canterbury, 2009. / Typescript (photocopy). Includes bibliographical references (p. 109-120). Also available via the World Wide Web.

Thesis (M.S.)--University of Wisconsin--Madison, 1984. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 153-162).

Surface heterogeneities cause differential heating that can generate mesoscale convective boundaries, sometimes leading to cloud development and enhanced localized precipitation. A preferred cloud pattern has been identified across Maryland and the Delmarva Peninsula region from 1998-2006 through the detection of cumuliform clouds on days when synoptic-scale forcing is weak. Hourly visible Geostationary Operational Environmental Satellite (GOES) imagery data are used to identify convective cloud masses. This allows quantitative description of the frequency and spatiotemporal extent of the clouds, helping forecasters gain insight into when and where they are likely to develop. Despite the inability to determine the underlying causes of the distinct cloud pattern, primarily due to the complex land cover, results indicate that the land receives significantly higher average total cloud cover than the Chesapeake Bay with Delaware receiving the highest average total cloud cover per state. Average total precipitation amounts follow this same trend on synoptically-weak days.

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