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Ronald L. Holle - One of the best experts on this subject based on the ideXlab platform.
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Seasonal, Monthly, and Weekly Distributions of NLDN and GLD360 Cloud-to-Ground Lightning
Monthly Weather Review, 2016Co-Authors: Ronald L. Holle, Kenneth L. Cummins, William A. BrooksAbstract:AbstractAnnual maps of Cloud-to-Ground Lightning flash density have been produced since the deployment of the National Lightning Detection Network (NLDN). However, a comprehensive national summary of seasonal, monthly, and weekly Lightning across the contiguous United States has not been developed. Cloud-to-Ground Lightning is not uniformly distributed in time, space, or frequency. Knowledge of these variations is useful for understanding meteorological processes responsible for Lightning occurrence, planning outdoor events, anticipating impacts of Lightning on power reliability, and relating to severe weather. To address this gap in documentation of Lightning occurrence, the variability on seasonal, monthly, and weekly scales is first addressed with NLDN flash data from 2005 to 2014 for the 48 states and adjacent regions. Flash density and the percentage of each season’s portion of the annual total are compiled. In spring, thunderstorms occur most often over southeastern states. Lightning spreads north a...
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Diurnal Variations of NLDN-Reported Cloud-to-Ground Lightning in the United States
Monthly Weather Review, 2014Co-Authors: Ronald L. HolleAbstract:AbstractNational maps of Cloud-to-Ground Lightning flash density (in flashes per square kilometer per year) for one or more years have been produced since the National Lightning Detection Network (NLDN) was first deployed across the contiguous United States in 1989. However, no single publication includes maps of Cloud-to-Ground flash density across the domain and adjacent areas during the entire diurnal cycle. Cloud-to-Ground Lightning has strong and variable diurnal changes across the United States that should be taken into account for outdoor Lightning-vulnerable activities, particularly those involving human safety. For this study, NLDN Cloud-to-Ground flash data were compiled in 20 km by 20 km grid squares from 2005 to 2012 for the lower 48 states. A unique feature of this study is that maps were prepared to coincide with local time, not time zones. NLDN flashes were assigned to 2-h time periods in 5° longitude bands. Composite maps of the 2-h periods with the most Lightning in each grid square were ...
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Lightning warnings with NLDN cloud and Cloud-to-Ground Lightning data
2014 International Conference on Lightning Protection (ICLP), 2014Co-Authors: Ronald L. Holle, Nicholas W.s. DemetriadesAbstract:Previous studies [1,2] have evaluated the performance of the U.S. National Lightning Detection Network (NLDN) with respect to warnings of Cloud-to-Ground Lightning (CG) at specific locations such as airports. The statistics used to evaluate warning performance have included probability of detection (POD), false alarm ratio (FAR), duration of warnings, and number of storms reported. In 2013, the NLDN was upgraded to Vaisala's LS7002 sensors replacing the older generation LS7001 and IMPACT sensors. As a result of this upgrade, the NLDN is expected to have a 50% cloud flash detection efficiency and a 95% Cloud-to-Ground flash detection efficiency [3]. In this study, we examine the warning performance using cloud and Cloud-to-Ground data from the NLDN after the 2013 upgrade. Data from several regions of the continental U.S. are considered. The warning statistics are evaluated with and without cloud Lightning data. The impact of varying outer radii, inner verification areas, and end-of-storm wait times are examined. Upon conclusion of the study, it was found that addition of NLDN cloud Lightning added about 10% to the POD, while the FAR was unchanged, and the percent time under valid warning and false alarms increased somewhat. As found previously, a 15-minute warning expiration time was better than 10 minutes, and POD decreased steadily for longer lead times for CG Lightning. POD increased steadily for larger outer radii, but FAR also increased. Finally, a short exploration of a smaller warning area showed better warning statistics, but there was significant sensitivity to the relative size of the inner versus outer areas.
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Surface wind convergence as a short-term predictor of Cloud-to-Ground Lightning at Kennedy Space Center
Weather and Forecasting, 1991Co-Authors: Andrew I. Watson, Ronald L. Holle, Raúl E. López, Robert Ortiz, James R. NicholsonAbstract:Abstract Cloud-to-Ground Lightning is a significant forecast problem at the Kennedy Space Center (KSC) in Florida. In this study, Cloud-to-Ground Lightning is related in time and space to surface convergence for 244 days during the convective seasons of 1985 and 1986 over a 790-km2 network at KSC. The method uses surface convergence, particularly the average over the area, to identify the potential for new, local thunderstorm growth, and it can be used to specify the likely time and location of Lightning during the life cycle of the convection. A threshold of 75×10−6 s−1 change in divergence is the main criterion used to define a convergence event, and a set of flashes less than 30 min apart defines a Lightning event. Time intervals are found from the study to be approximately 1 h from beginning convergence to first flash, and another hour to the end of Lightning. The influences of low-level winds and midlevel moisture in determining the location and intensity of convection are discussed. This is the firs...
Donald R. Macgorman - One of the best experts on this subject based on the ideXlab platform.
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Positive Cloud-to-Ground Lightning in Tornadic Storms and Hailstorms
Monthly Weather Review, 1994Co-Authors: Donald R. Macgorman, Donald W. BurgessAbstract:Abstract Although negative ground flashes usually dominate Cloud-to-Ground Lightning activity, positive ground flashes can dominate in some severe storms for periods ranging from 30 min to several hours. Unlike most other types of storms in which positive ground flashes occur, severe storms can have positive flash rates and densities of strike points comparable to those usually observed for negative ground flashes in active thunderstorms. Fifteen such storms are analyzed in this paper to examine relationships of positive ground flashes to various storm characteristics, especially reports of large hail and tornadoes. In 4 of the 15 storms, ground flash activity was dominated by positive Cloud-to-Ground Lightning throughout most of the life of the storm. In 11 storms, the dominant polarity of ground flashes switched from positive to negative sometime during the mature stage of the storm. In all cases observed by Doppler radar, storms dominated by positive flashes had at least some rotation, and in most case...
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Cloud-to-Ground Lightning in a Tornadic Storm on 8 May 1986
Monthly Weather Review, 1991Co-Authors: Donald R. Macgorman, K. NielsenAbstract:Abstract On 8 May 1986, the National Severe Storms Laboratory (NSSL) collected Doppler radar and Lightning ground strike data on a supercell storm that produced three tornadoes, including an F3 tornado in Edmond, Oklahoma, approximately 40 km north of NSSL. The Edmond storm formed 30 km ahead of a storm complex and produced its first and most damaging tornado just as the storm complex began to overtake it from the west. In the mesocyclone that spawned the tornado, low-level cyclonic shear peaked as the first tornado dissipated and a second tornado began. As low-level cyclonic shear initially increased, negative Cloud-to-Ground Lightning flash rates also increased, reaching a peak of 11 min−1 a few minutes after the peak in cyclonic shear. During this period Lightning strike locations tended to concentrate just north of the mesocyclone, near and inside a 50-dBZ reflectivity core. As cyclonic shear decreased from its peak during and after the second tornado, negative ground flash rates also decreased, and s...
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The Evolution of a Severe Mesoscale Convective System: Cloud-to-Ground Lightning Location and Storm Structure
Monthly Weather Review, 1991Co-Authors: Stephen J. Keighton, Howard B. Bluestein, Donald R. MacgormanAbstract:Abstract Cloud-to-Ground Lightning-location data are correlated with the Doppler-radar-observed structure of the evolution of a severe mesoscale convective system in Oklahoma on 23 May 1981. While many of the results are not new, this study is unique in that the evolution of electrical activity in a severe storm is compared to storm structure for most of the storm's life. The, first storm formed ahead of a mesoscale low pressure area located at the intersection of a front and a dryline, and developed into a tornadic supercell in an environment of locally enhanced vertical shear. Ordinary cells subsequently formed both to the southwest and northeast of the supercell along the dryline and the front, respectively, and merged with the supercell to form a squall line having a trailing stratiform precipitation region with midlevel rear inflow. It is shown that the Cloud-to-Ground flash rate in the convective region is related to the apparent strength of the updraft. Before the storm became a supercell, the ligh...
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Positive Cloud-to-Ground Lightning in Mesoscale Convective Systems
Journal of the Atmospheric Sciences, 1990Co-Authors: Steven A. Rutledge, Chungu Lu, Donald R. MacgormanAbstract:Abstract We have examined the characteristics of positive Cloud-to-Ground Lightning flashes in Mesoscale Convective Systems observed during the Oklahoma-Kansas PRE-STORM project in 1985. Lightning frequencies and patterns of ground strike locations are related to observed storm precipitation structures, with emphasis placed on relating observed Lightning patterns to the stratiform precipitation regions. Positive ground flashes are categorized in relation to their position relative to storm radar echo patterns, and frequency of occurrence relative to storm lifecycles. Observations presented indicate that many of the positive flashes are likely produced by the advection of positive charge from the upper levels of the convective portions of the storm. We suggest that an additional class of positive ground flashes are associated with the generation of charge by stratiform precipitation processes, specifically related to ice-ice interactions in regions of low supercooled liquid water contents. A simple one-dim...
Steven A. Rutledge - One of the best experts on this subject based on the ideXlab platform.
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On the relationship between cloud‐to‐ground Lightning and convective rainfall
Journal of Geophysical Research, 1998Co-Authors: Walter A. Petersen, Steven A. RutledgeAbstract:Ratios of area mean rainfall and Cloud-to-Ground Lightning flash count (termed rain yields) were computed for several different locations around the globe, over temporal and spatial scales of 1 month and 10 4 -10 5 km 2 , respectively. Values of the rain yield clustered near 10 8 kg/fl for a large portion of the midcontinental United States. Rain yields were slightly lower over the arid southwestern United States, averaging ∼6 × 10 7 kg/fl. In tropical locations the rain yields increased systematically from a tropical continental value of 4 × 10 8 kg/fl to a value of 10 10 kg/fl for the tropical western Pacific Ocean. The observed stability of the rain yield, coupled with demonstrated positive correlations between Cloud-to-Ground flash density and rainfall amount, suggests that Cloud-to-Ground Lightning data may be useful for inferring monthly convective rainfall statistics in certain rainfall regimes.
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Vertical Radar Reflectivity Structure and Cloud-to-Ground Lightning in the Stratiform Region of MCSs: Further Evidence for In Situ Charging in the Stratiform Region
Monthly Weather Review, 1994Co-Authors: Steven A. Rutledge, Walter A. PetersenAbstract:Abstract This study presents further evidence in support of an in situ, noninductive charging mechanism as the process likely responsible for significant electrification of the trailing stratiform regions of mesoscale convective systems (MCSs). In contrast to previous studies of MCS electrification that have investigated observations of radar reflectivity and Cloud-to-Ground Lightning in the horizontal (e.g., Orville et al.; Rutledge et al.), here the relationship between the location and occurrence of Cloud-to-Ground Lightning in the stratiform regions of midlatitude and tropical MCSs and the vertical profile of radar reflectivity are examined. The vertical profile of radar reflectivity at elevations above the 0°C level is used as a proxy for the amount of mass present in the mixed-phase region of the stratiform clouds, which in turn is related to the generation of charge through a noninductive charging mechanism. To further explore the relationship between radar reflectivity, mixed-phase microphysics, a...
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Positive Cloud-to-Ground Lightning in Mesoscale Convective Systems
Journal of the Atmospheric Sciences, 1990Co-Authors: Steven A. Rutledge, Chungu Lu, Donald R. MacgormanAbstract:Abstract We have examined the characteristics of positive Cloud-to-Ground Lightning flashes in Mesoscale Convective Systems observed during the Oklahoma-Kansas PRE-STORM project in 1985. Lightning frequencies and patterns of ground strike locations are related to observed storm precipitation structures, with emphasis placed on relating observed Lightning patterns to the stratiform precipitation regions. Positive ground flashes are categorized in relation to their position relative to storm radar echo patterns, and frequency of occurrence relative to storm lifecycles. Observations presented indicate that many of the positive flashes are likely produced by the advection of positive charge from the upper levels of the convective portions of the storm. We suggest that an additional class of positive ground flashes are associated with the generation of charge by stratiform precipitation processes, specifically related to ice-ice interactions in regions of low supercooled liquid water contents. A simple one-dim...
Richard E. Orville - One of the best experts on this subject based on the ideXlab platform.
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Radar Nowcasting of Cloud-to-Ground Lightning over Houston, Texas
Weather and Forecasting, 2011Co-Authors: Richard M. Mosier, Courtney Schumacher, Richard E. Orville, Lawrence D. CareyAbstract:AbstractTen years (1997–2006) of summer (June–August) daytime (1400–0000 UTC) Weather Surveillance Radar-1988 Doppler data for Houston, Texas, were examined to determine the best radar-derived predictors of the first Cloud-to-Ground Lightning flash from a convective cell. 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°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 67 384 unique cells and 1 028 510 Lightning flashes to find the best Lightning forecast criter...
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Enhancement of cloud‐to‐ground Lightning over Houston, Texas
Geophysical Research Letters, 2001Co-Authors: Richard E. Orville, Gary R. Huffines, John W. Nielsen-gammon, Renyi Zhang, Scott M. Steiger, Stephen Phillips, Steve Allen, William L. ReadAbstract:Cloud-to-Ground Lightning flash data have been analyzed for the twelve-year period 1989–2000, for a geographical area centered on Houston, Texas. Of the 1.6 million Cloud-to-Ground flashes in this area of study, approximately 752,000 flashes occurred in the summer months of June, July, and August, and 119,000 flashes in the months of December, January, and February. The highest flash densities, greater than 4 flashes km−2 in the summer and 0.7 flashes/km−2 in the winter, are near the urban areas of Houston. We suggest that the elevated flash densities could result from several factors, including, 1) the convergence due to the urban heat island effect, and 2) the increasing levels of air pollution from anthropogenic sources producing numerous small droplets and thereby suppressing mean droplet size. The latter effect would enable more cloud water to reach the mixed phase region where it is involved in the formation of precipitation and the separation of electric charge, leading to an enhancement of Lightning.
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Cloud-to-Ground Lightning in the United States: NLDN results in the first decade, 1989-98
Monthly Weather Review, 2001Co-Authors: Richard E. Orville, Gary R. HuffinesAbstract:Abstract The physical and geographical characteristics of over 216 million Cloud-to-Ground Lightning flashes recorded during the first decade (1989–98) of operation of the National Lightning Detection Network (NLDN) covering the entire continental United States are presented. These characteristics include the total Cloud-to-Ground flash density, the positive flash density, the percentage of positive flashes, the first stroke negative and positive peak currents, and the multiplicity for negative and positive flashes. All analyses were done with a spatial resolution of 0.2° corresponding to an approximate resolution of 20 km. Flash densities were not corrected for detection efficiency; the measured values are presented. The maximum measured flash density is found to exceed 9 flashes km−2 across Florida in the Tampa–Orlando–Cape Canaveral corridor, near Fort Myers, and between Lake Okeechobee and the Atlantic Ocean. The mean monthly flash count peaks in July at approximately 5.5 million flashes. Positive fla...
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Cloud-to-Ground Lightning in tropical cyclones: A study of Hurricanes Hugo (1989) and Jerry (1989)
Monthly Weather Review, 1994Co-Authors: Christopher E. Samsury, Richard E. OrvilleAbstract:Abstract Cloud-to-Ground Lightning characteristics of two Atlantic cyclones of 1989, Hurricanes Hugo and Jerry, are presented. Statistics on the number of flashes, location, polarity, peak currents, and multiplicity (number of strokes per flash) are examined in an 18-h period divided into prelandfall and postlandfall categories. Land-based and aircraft lower fuselage radar data are also analyzed to determine the nature of the precipitation in which Lightning is detected. Jerry is found to be more electrically active than Hugo, with 691 flashes detected compared with 33 flashes for Hugo. The majority of these flashes, regardless of the polarity, are located in the right front and right rear quadrants of the hurricanes, almost exclusively in outer convective rainbands. One reason for the large difference in the number of flashes between the two storms is the presence of many convective rainbands in Jerry, compared to only a few in Hugo. More than 20% of the flashes in each storm have a positive polarity. Me...
Walter A. Petersen - One of the best experts on this subject based on the ideXlab platform.
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On the relationship between cloud‐to‐ground Lightning and convective rainfall
Journal of Geophysical Research, 1998Co-Authors: Walter A. Petersen, Steven A. RutledgeAbstract:Ratios of area mean rainfall and Cloud-to-Ground Lightning flash count (termed rain yields) were computed for several different locations around the globe, over temporal and spatial scales of 1 month and 10 4 -10 5 km 2 , respectively. Values of the rain yield clustered near 10 8 kg/fl for a large portion of the midcontinental United States. Rain yields were slightly lower over the arid southwestern United States, averaging ∼6 × 10 7 kg/fl. In tropical locations the rain yields increased systematically from a tropical continental value of 4 × 10 8 kg/fl to a value of 10 10 kg/fl for the tropical western Pacific Ocean. The observed stability of the rain yield, coupled with demonstrated positive correlations between Cloud-to-Ground flash density and rainfall amount, suggests that Cloud-to-Ground Lightning data may be useful for inferring monthly convective rainfall statistics in certain rainfall regimes.
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Vertical Radar Reflectivity Structure and Cloud-to-Ground Lightning in the Stratiform Region of MCSs: Further Evidence for In Situ Charging in the Stratiform Region
Monthly Weather Review, 1994Co-Authors: Steven A. Rutledge, Walter A. PetersenAbstract:Abstract This study presents further evidence in support of an in situ, noninductive charging mechanism as the process likely responsible for significant electrification of the trailing stratiform regions of mesoscale convective systems (MCSs). In contrast to previous studies of MCS electrification that have investigated observations of radar reflectivity and Cloud-to-Ground Lightning in the horizontal (e.g., Orville et al.; Rutledge et al.), here the relationship between the location and occurrence of Cloud-to-Ground Lightning in the stratiform regions of midlatitude and tropical MCSs and the vertical profile of radar reflectivity are examined. The vertical profile of radar reflectivity at elevations above the 0°C level is used as a proxy for the amount of mass present in the mixed-phase region of the stratiform clouds, which in turn is related to the generation of charge through a noninductive charging mechanism. To further explore the relationship between radar reflectivity, mixed-phase microphysics, a...