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Abstract
Cloud-to-ground lightning data have been analyzed for the years 1998–2000 for North America (Canada plus the contiguous United States) for all ground flashes, positive flashes, the percentage of positive lightning, peak currents for negative and positive lightning, and for negative and positive multiplicity. The authors examined a total of 88.7 million flashes divided among the three years: 31.1 million (1998), 29.5 million (1999), and 28.2 million (2000). Annual flash densities are derived from 245–424 km2 regions and are uncorrected for flash detection efficiency. The highest flash densities in Canada are along the U.S.–Canadian border (1–3 flashes km−2), and in the United States along the Gulf of Mexico coast and Florida (exceeding 9 flashes km−2). Maximum annual positive flash densities in Canada generally range primarily from 0.1 to 0.3 flashes km−2, and in the United States to over 0.7 flashes km−2 (areas in the Midwest, the Gulf Coast, and Florida). Areas of greater than 20% positive lightning occur throughout British Columbia and the midwest United States extending into Manitoba and Ontario. High percent positive also occurs in Quebec and much of eastern Canada. The median negative peak current is 16.5 kA. The median positive peak current, with the peak currents less than 10 kA removed from the calculation, is 19.8 kA. Median positive peak currents exceed 35 kA in the Midwest from west Texas to Nebraska to the Canadian border. The area of maximum mean negative multiplicity, exceeding 2.6 strokes, occurs in western Canada from just east of the British Columbia–Alberta border to and including Saskatchewan. Mean negative multiplicity also peaks in the southeastern United States. Mean positive multiplicity is observed to have maximum values in Alberta, Saskatchewan, and in a region centered on Tennessee. The authors examined the time of maximum flash rate in North America and find it is over land in the daytime hours with the exception of a region of maximum nighttime lightning in midcontinent that extends from the midwestern United States into Canada. Over the waters surrounding the North American continent, the maximum lightning is principally at night, including the coastal Pacific, the Gulf of California, the Gulf of Mexico, and the coastal waters of the North Atlantic.
Abstract
Cloud-to-ground lightning data have been analyzed for the years 1998–2000 for North America (Canada plus the contiguous United States) for all ground flashes, positive flashes, the percentage of positive lightning, peak currents for negative and positive lightning, and for negative and positive multiplicity. The authors examined a total of 88.7 million flashes divided among the three years: 31.1 million (1998), 29.5 million (1999), and 28.2 million (2000). Annual flash densities are derived from 245–424 km2 regions and are uncorrected for flash detection efficiency. The highest flash densities in Canada are along the U.S.–Canadian border (1–3 flashes km−2), and in the United States along the Gulf of Mexico coast and Florida (exceeding 9 flashes km−2). Maximum annual positive flash densities in Canada generally range primarily from 0.1 to 0.3 flashes km−2, and in the United States to over 0.7 flashes km−2 (areas in the Midwest, the Gulf Coast, and Florida). Areas of greater than 20% positive lightning occur throughout British Columbia and the midwest United States extending into Manitoba and Ontario. High percent positive also occurs in Quebec and much of eastern Canada. The median negative peak current is 16.5 kA. The median positive peak current, with the peak currents less than 10 kA removed from the calculation, is 19.8 kA. Median positive peak currents exceed 35 kA in the Midwest from west Texas to Nebraska to the Canadian border. The area of maximum mean negative multiplicity, exceeding 2.6 strokes, occurs in western Canada from just east of the British Columbia–Alberta border to and including Saskatchewan. Mean negative multiplicity also peaks in the southeastern United States. Mean positive multiplicity is observed to have maximum values in Alberta, Saskatchewan, and in a region centered on Tennessee. The authors examined the time of maximum flash rate in North America and find it is over land in the daytime hours with the exception of a region of maximum nighttime lightning in midcontinent that extends from the midwestern United States into Canada. Over the waters surrounding the North American continent, the maximum lightning is principally at night, including the coastal Pacific, the Gulf of California, the Gulf of Mexico, and the coastal waters of the North Atlantic.
Abstract
A significant winter precipitation event occurred on 8–9 March 1994 in Oklahoma. Snow accumulations greater than 30 cm (12 in.) were measured within a narrow corridor in northern Oklahoma. On the synoptic scale and mesoscale, a correspondence between large snow accumulations and 600-hPa frontogenesis was revealed; the precipitation was formed above the cold frontal surface, owing to midtropospheric ascent associated with the cross-frontal circulation in a region of elevated conditional instability. The location of such a narrow corridor of large accumulations was not, however, disclosed by any patterns in the radar reflectivity data. Indeed, during this event, an elongated maximum of snow accumulation was not associated with a persistent “band” of enhanced reflectivity and vice versa.
Dual-polarization and dual-Doppler radar data allowed for a novel analysis of winter precipitation processes and structures, within the context of the larger-scale diagnosis. It was possible to identify, in order of distance southward toward the surface cold front: (i) an elevated convective element, which was classified as an elevated thunderstorm and may have functioned as an ice crystal “generator” cell, embedded within a broad region of generally stratiform precipitation; (ii) a reflectivity band and associated rain–snow transition zone, the evolution and structure of which apparently were coupled to the effects of melting precipitation and strong vertical wind shear; and (iii) a mixed-phase precipitation-generating, prolific lightning-producing, nonelevated thunderstorm cell that was sustained in the postfrontal air in part by virtue of its rotational dynamics.
Abstract
A significant winter precipitation event occurred on 8–9 March 1994 in Oklahoma. Snow accumulations greater than 30 cm (12 in.) were measured within a narrow corridor in northern Oklahoma. On the synoptic scale and mesoscale, a correspondence between large snow accumulations and 600-hPa frontogenesis was revealed; the precipitation was formed above the cold frontal surface, owing to midtropospheric ascent associated with the cross-frontal circulation in a region of elevated conditional instability. The location of such a narrow corridor of large accumulations was not, however, disclosed by any patterns in the radar reflectivity data. Indeed, during this event, an elongated maximum of snow accumulation was not associated with a persistent “band” of enhanced reflectivity and vice versa.
Dual-polarization and dual-Doppler radar data allowed for a novel analysis of winter precipitation processes and structures, within the context of the larger-scale diagnosis. It was possible to identify, in order of distance southward toward the surface cold front: (i) an elevated convective element, which was classified as an elevated thunderstorm and may have functioned as an ice crystal “generator” cell, embedded within a broad region of generally stratiform precipitation; (ii) a reflectivity band and associated rain–snow transition zone, the evolution and structure of which apparently were coupled to the effects of melting precipitation and strong vertical wind shear; and (iii) a mixed-phase precipitation-generating, prolific lightning-producing, nonelevated thunderstorm cell that was sustained in the postfrontal air in part by virtue of its rotational dynamics.
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 first known dynamically-based forecast method for lightning prediction. The technique, currently in use at KSC, has been shown to be a systematic, quantitative tool for predicting lightning onset in situations where conventional analysis tools such as radar and satellite are limited.
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 first known dynamically-based forecast method for lightning prediction. The technique, currently in use at KSC, has been shown to be a systematic, quantitative tool for predicting lightning onset in situations where conventional analysis tools such as radar and satellite are limited.
Abstract
Cloud-to-ground lightning is a significant meteorological problem at the Kennedy Space Center (KSC). Of particular importance is the growth of lightning-bearing clouds in the vicinity of KSC, for which warnings must be considered on a daily basis. In this study, lightning was related in time and space with surface convergence for 42 days during the summer of 1983 over a 280 km2 analysis area at KSC. Several events are examined in detail. Previous studies in south Florida have shown that a signature in the surface convergence field frequently precedes convective precipitation; however, the 1983 KSC data constitute the first dataset interrelating the surface wind field, radar echoes, and lightning. It is emphasized that a larger surface-wind network is needed to validate these preliminary result, together with monitoring and understanding the synoptic-scale situation based on upper-air and other reports in the region.
Abstract
Cloud-to-ground lightning is a significant meteorological problem at the Kennedy Space Center (KSC). Of particular importance is the growth of lightning-bearing clouds in the vicinity of KSC, for which warnings must be considered on a daily basis. In this study, lightning was related in time and space with surface convergence for 42 days during the summer of 1983 over a 280 km2 analysis area at KSC. Several events are examined in detail. Previous studies in south Florida have shown that a signature in the surface convergence field frequently precedes convective precipitation; however, the 1983 KSC data constitute the first dataset interrelating the surface wind field, radar echoes, and lightning. It is emphasized that a larger surface-wind network is needed to validate these preliminary result, together with monitoring and understanding the synoptic-scale situation based on upper-air and other reports in the region.
Abstract
This study addresses winter season lightning by examining synoptic-scale circulations, cloud-to-ground (CG) lightning patterns, and frozen precipitation. Specifically, locations, frequencies, and polarities of CG flashes are related to the location, intensity, and type of heavy frozen precipitation (snow, freezing rain, or ice pellets) for seven winter storms affecting the southeast United States from 1994 through 1997. The results suggest two distinct phases of winter storm development, each producing different patterns of CG lightning and frozen precipitation. These phases are termed the arctic front (AF) and migratory cyclone (MC) types.
Analysis was performed on 27 periods within the seven cases. In several periods, there were significant numbers of CG flashes within or near a subfreezing surface air mass and frozen precipitation when a quasi-stationary arctic front existed. These periods were classified as AF phases. This flash pattern indicates a connection between the intensity of convection (associated with CG flashes) and downwind frozen precipitation. In these situations there was strong southwesterly flow aloft, which may have advected ice particles from these convective clouds into stratiform clouds near the frontal surface. This process resembles the “seeder–feeder” mechanism of precipitation growth.
The AF phases eventually developed into MC phases, and the latter were more common in this study. The MC phases in general exhibit a different spatial relationship between CG lightning and heavy frozen precipitation; that is, CG flashes retreat toward the warm sector of the cyclone and thus are not proximal to the 0°C surface isotherm. There appears to be little connection between convection and frozen precipitation in most of these situations. The distinction between AF and MC phases, in conjunction with CG lightning monitoring, may aid forecasts of the duration and amount of frozen precipitation during winter storms.
Abstract
This study addresses winter season lightning by examining synoptic-scale circulations, cloud-to-ground (CG) lightning patterns, and frozen precipitation. Specifically, locations, frequencies, and polarities of CG flashes are related to the location, intensity, and type of heavy frozen precipitation (snow, freezing rain, or ice pellets) for seven winter storms affecting the southeast United States from 1994 through 1997. The results suggest two distinct phases of winter storm development, each producing different patterns of CG lightning and frozen precipitation. These phases are termed the arctic front (AF) and migratory cyclone (MC) types.
Analysis was performed on 27 periods within the seven cases. In several periods, there were significant numbers of CG flashes within or near a subfreezing surface air mass and frozen precipitation when a quasi-stationary arctic front existed. These periods were classified as AF phases. This flash pattern indicates a connection between the intensity of convection (associated with CG flashes) and downwind frozen precipitation. In these situations there was strong southwesterly flow aloft, which may have advected ice particles from these convective clouds into stratiform clouds near the frontal surface. This process resembles the “seeder–feeder” mechanism of precipitation growth.
The AF phases eventually developed into MC phases, and the latter were more common in this study. The MC phases in general exhibit a different spatial relationship between CG lightning and heavy frozen precipitation; that is, CG flashes retreat toward the warm sector of the cyclone and thus are not proximal to the 0°C surface isotherm. There appears to be little connection between convection and frozen precipitation in most of these situations. The distinction between AF and MC phases, in conjunction with CG lightning monitoring, may aid forecasts of the duration and amount of frozen precipitation during winter storms.
Abstract
Cloud-to-ground lightning flash characteristics of a series of four mesoscale convective systems (MCS) that occurred in Oklahoma and Kansas on 3–4 June 1985 during the Oklahoma-Kansas Preliminary Regional Experiment for STORM-Central project are described. A total of 23 490 flashes were detected by the network from all four MCSs; 96% of them lowered negative charge to ground. Because the second MCS (MCS II) spent nearly all of its lifetime within the optimal region of coverage of the lightning and radar networks, trends in ground-flash characteristics could be documented throughout the system's life cycle. Lightning trends were analyzed relative to rainfall parameters based on radar network data and were stratified by the flashes’ polarity and locations according to their association with convective and stratiform radar echoes.
Most flashes in the second MCS were negative ground strikes within convective radar echoes. In convective regions the flashes were primarily negative; in stratiform regions the negatives were somewhat more than half the flashes. Positive flashes were much less frequent than negative ground strikes for the entire storm. Positive strikes in stratiform echoes during the last half of the storm exceeded the number of negative flashes, but positive ground strikes were always scarce in convective regions. For the second MCS, time series of flashes were developed for flash density, flash rate per rain volume, and number according to radar echo type. Severe weather tended to occur during the growth and mature stages of the storm and was located on the southern and western sides of the MCS's lightning activity. During the growth stage, smaller elements within the new storm had a somewhat linear organization of frequent negative flashes in convective echoes. During the mature stage, negative flashes were in a large cluster, their rates peaked, and then began to decrease. During the decay stage, negative flash rates rapidly decreased but continued to cluster in convective regions. At most, a few percent of the flashes in convective regions lowered positive charge to ground, and positive flash rates in convective regions followed trends very similar to those of negative flash rates. Positive flash rates in the stratiform region, however, tended to increase until early in the decay stage. In the stratiform region during the decay stage, positive flashes were spread over a much larger area than negative flashes.
Abstract
Cloud-to-ground lightning flash characteristics of a series of four mesoscale convective systems (MCS) that occurred in Oklahoma and Kansas on 3–4 June 1985 during the Oklahoma-Kansas Preliminary Regional Experiment for STORM-Central project are described. A total of 23 490 flashes were detected by the network from all four MCSs; 96% of them lowered negative charge to ground. Because the second MCS (MCS II) spent nearly all of its lifetime within the optimal region of coverage of the lightning and radar networks, trends in ground-flash characteristics could be documented throughout the system's life cycle. Lightning trends were analyzed relative to rainfall parameters based on radar network data and were stratified by the flashes’ polarity and locations according to their association with convective and stratiform radar echoes.
Most flashes in the second MCS were negative ground strikes within convective radar echoes. In convective regions the flashes were primarily negative; in stratiform regions the negatives were somewhat more than half the flashes. Positive flashes were much less frequent than negative ground strikes for the entire storm. Positive strikes in stratiform echoes during the last half of the storm exceeded the number of negative flashes, but positive ground strikes were always scarce in convective regions. For the second MCS, time series of flashes were developed for flash density, flash rate per rain volume, and number according to radar echo type. Severe weather tended to occur during the growth and mature stages of the storm and was located on the southern and western sides of the MCS's lightning activity. During the growth stage, smaller elements within the new storm had a somewhat linear organization of frequent negative flashes in convective echoes. During the mature stage, negative flashes were in a large cluster, their rates peaked, and then began to decrease. During the decay stage, negative flash rates rapidly decreased but continued to cluster in convective regions. At most, a few percent of the flashes in convective regions lowered positive charge to ground, and positive flash rates in convective regions followed trends very similar to those of negative flash rates. Positive flash rates in the stratiform region, however, tended to increase until early in the decay stage. In the stratiform region during the decay stage, positive flashes were spread over a much larger area than negative flashes.
Abstract
A World Meteorological Organization weather and climate extremes committee has judged that the world’s longest reported distance for a single lightning flash occurred with a horizontal distance of 321 km (199.5 mi) over Oklahoma in 2007, while the world’s longest reported duration for a single lightning flash is an event that lasted continuously for 7.74 s over southern France in 2012. In addition, the committee has unanimously recommended amendment of the AMS Glossary of Meteorology definition of lightning discharge as a “series of electrical processes taking place within 1 s” by removing the phrase “within 1 s” and replacing it with “continuously.” Validation of these new world extremes 1) demonstrates the recent and ongoing dramatic augmentations and improvements to regional lightning detection and measurement networks, 2) provides reinforcement regarding the dangers of lightning, and 3) provides new information for lightning engineering concerns.
Abstract
A World Meteorological Organization weather and climate extremes committee has judged that the world’s longest reported distance for a single lightning flash occurred with a horizontal distance of 321 km (199.5 mi) over Oklahoma in 2007, while the world’s longest reported duration for a single lightning flash is an event that lasted continuously for 7.74 s over southern France in 2012. In addition, the committee has unanimously recommended amendment of the AMS Glossary of Meteorology definition of lightning discharge as a “series of electrical processes taking place within 1 s” by removing the phrase “within 1 s” and replacing it with “continuously.” Validation of these new world extremes 1) demonstrates the recent and ongoing dramatic augmentations and improvements to regional lightning detection and measurement networks, 2) provides reinforcement regarding the dangers of lightning, and 3) provides new information for lightning engineering concerns.
Abstract
A World Meteorological Organization (WMO) Commission for Climatology international panel was convened to examine and assess the available evidence associated with five weather-related mortality extremes: 1) lightning (indirect), 2) lightning (direct), 3) tropical cyclones, 4) tornadoes, and 5) hail. After recommending for acceptance of only events after 1873 (the formation of the predecessor of the WMO), the committee evaluated and accepted the following mortality extremes: 1) “highest mortality (indirect strike) associated with lightning” as the 469 people killed in a lightning-caused oil tank fire in Dronka, Egypt, on 2 November 1994; 2) “highest mortality directly associated with a single lightning flash” as the lightning flash that killed 21 people in a hut in Manica Tribal Trust Lands, Zimbabwe (at time of incident, eastern Rhodesia), on 23 December 1975; 3) “highest mortality associated with a tropical cyclone” as the Bangladesh (at time of incident, East Pakistan) cyclone of 12–13 November 1970 with an estimated death toll of 300 000 people; 4) “highest mortality associated with a tornado” as the 26 April 1989 tornado that destroyed the Manikganj district, Bangladesh, with an estimated death toll of 1300 individuals; and 5) “highest mortality associated with a hailstorm” as the storm occurring near Moradabad, India, on 30 April 1888 that killed 246 people. These mortality extremes serve to further atmospheric science by giving baseline mortality values for comparison to future weather-related catastrophes and also allow for adjudication of new meteorological information as it becomes available.
Abstract
A World Meteorological Organization (WMO) Commission for Climatology international panel was convened to examine and assess the available evidence associated with five weather-related mortality extremes: 1) lightning (indirect), 2) lightning (direct), 3) tropical cyclones, 4) tornadoes, and 5) hail. After recommending for acceptance of only events after 1873 (the formation of the predecessor of the WMO), the committee evaluated and accepted the following mortality extremes: 1) “highest mortality (indirect strike) associated with lightning” as the 469 people killed in a lightning-caused oil tank fire in Dronka, Egypt, on 2 November 1994; 2) “highest mortality directly associated with a single lightning flash” as the lightning flash that killed 21 people in a hut in Manica Tribal Trust Lands, Zimbabwe (at time of incident, eastern Rhodesia), on 23 December 1975; 3) “highest mortality associated with a tropical cyclone” as the Bangladesh (at time of incident, East Pakistan) cyclone of 12–13 November 1970 with an estimated death toll of 300 000 people; 4) “highest mortality associated with a tornado” as the 26 April 1989 tornado that destroyed the Manikganj district, Bangladesh, with an estimated death toll of 1300 individuals; and 5) “highest mortality associated with a hailstorm” as the storm occurring near Moradabad, India, on 30 April 1888 that killed 246 people. These mortality extremes serve to further atmospheric science by giving baseline mortality values for comparison to future weather-related catastrophes and also allow for adjudication of new meteorological information as it becomes available.
