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2. Introduction to Special Collection "The Exceptional Arctic Stratospheric Polar Vortex in 2019/2020: Causes and Consequences".
- Author
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Manney, Gloria L., Butler, Amy H., Wargan, Krzysztof, and Grooß, Jens‐Uwe
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POLAR vortex ,EXTREME weather ,SURFACE of the earth ,WEATHER ,ATMOSPHERIC boundary layer ,CHEMICAL processes - Abstract
This paper introduces the special collection in Geophysical Research Letters and Journal of Geophysical Research: Atmospheres on the exceptional stratospheric polar vortex in 2019/2020. Papers in this collection show that the 2019/2020 stratospheric polar vortex was the strongest, most persistent, and coldest on record in the Arctic. The unprecedented Arctic chemical processing and ozone loss in spring 2020 have been studied using numerous satellite and ground‐based data sets and chemistry‐transport models. Quantitative estimates of chemical loss are broadly consistent among the studies and show profile loss of about the same magnitude as in the Arctic in 2011, but with most loss at lower altitudes; column loss was comparable to or larger than that in 2011. Several papers show evidence of dynamical coupling from the mesosphere down to the surface. Studies of tropospheric influence and impacts link the exceptionally strong vortex to reflection of upward propagating waves and show coupling to tropospheric anomalies, including extreme heat, precipitation, windstorms, and marine cold air outbreaks. Predictability of the exceptional stratospheric polar vortex in 2019/2020 and related predictability of surface conditions are explored. The exceptionally strong stratospheric polar vortex in 2019/2020 highlights the extreme interannual variability in the Arctic winter/spring stratosphere and the far‐reaching consequences of such extremes. Plain Language Summary: The Arctic stratospheric polar vortex—a band of strong winds roughly encircling the pole at about 65°N latitude from about 15 to 50 km above the Earth's surface that forms every winter—was exceptionally strong during the 2019/2020 winter. The strong vortex in the stratosphere was linked to unusual conditions at both higher and lower altitudes. This collection of papers explores the far‐reaching consequences of the exceptionally strong stratospheric polar vortex in 2019/2020, including impacts on Arctic chemical ozone loss and on surface weather conditions. Chemical ozone loss in spring 2020 matched or exceeded the most previously on record (for 2011) and showed some features similar to the larger loss that occurs over the Antarctic every spring. The exceptionally strong stratospheric polar vortex was linked to weather extremes, including record heat, unusual patterns of precipitation, marine cold air outbreaks, and windstorms. Key Points: The stratospheric polar vortex in 2019/2020 was the strongest and longest‐lasting on record as described in this special collectionThis exceptionally strong and cold polar vortex led to unprecedented Arctic ozone loss, approaching that in some Antarctic wintersCirculation anomalies linked to the vortex spanned the mesosphere to the surface with implications for extreme weather and predictability [ABSTRACT FROM AUTHOR]
- Published
- 2022
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3. Multi‐Scale Kelvin‐Helmholtz Instability Dynamics Observed by PMC Turbo on 12 July 2018: 1. Secondary Instabilities and Billow Interactions.
- Author
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Kjellstrand, C. Bjorn, Fritts, David C., Miller, Amber D., Williams, Bifford P., Kaifler, Natalie, Geach, Christopher, Hanany, Shaul, Kaifler, Bernd, Jones, Glenn, Limon, Michele, Reimuller, Jason, and Wang, Ling
- Subjects
KELVIN-Helmholtz instability ,NOCTILUCENT clouds ,ATMOSPHERIC turbulence ,GRAVITY waves ,MIDDLE atmosphere ,KINEMATIC viscosity ,REYNOLDS number ,HELMHOLTZ resonators - Abstract
The Polar Mesospheric Cloud (PMC) Turbulence experiment performed optical imaging and Rayleigh lidar PMC profiling during a 6‐day flight in July 2018. A mosaic of seven imagers provided sensitivity to spatial scales from ∼20 m to 100 km at a ∼2‐s cadence. Lidar backscatter measurements provided PMC brightness profiles and enabled definition of vertical displacements of larger‐scale gravity waves (GWs) and smaller‐scale instabilities of various types. These measurements captured an interval of strong, widespread Kelvin‐Helmholtz instabilities (KHI) occurring over northeastern Canada on July 12, 2018 during a period of significant GW activity. This paper addresses the evolution of the KHI field and the characteristics and roles of secondary instabilities within the KHI. Results include the imaging of secondary KHI in the middle atmosphere and multiple examples of KHI "tube and knot" (T&K) dynamics where two or more KH billows interact. Such dynamics have been identified clearly only once in the atmosphere previously. Results reveal that KHI T&K arise earlier and evolve more quickly than secondary instabilities of uniform KH billows. A companion paper by Fritts et al. (2022), https://doi.org/10.1029/2021JD035834 reveals that they also induce significantly larger energy dissipation rates than secondary instabilities of individual KH billows. The expected widespread occurrence of KHI T&K events may have important implications for enhanced turbulence and mixing influencing atmospheric structure and variability. Key Points: First observation of unambiguous secondary Kelvin‐Helmholtz instabilities in high‐resolution images of the polar mesospheric cloud layerIdentification and quantification of Kelvin‐Helmholtz billow interactions leading to tubes and knots and accelerated billow breakdownEstimation of turbulence Reynolds number Returb ∼ 5,000 and νturb ∼ 3 times larger than the kinematic viscosity [ABSTRACT FROM AUTHOR]
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- 2022
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4. Recurrent Lightning Spots: Where Lightning Strikes More Than Twice.
- Author
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Sola, G., López, J. A., Montanyà, J., Pineda, N., and Williams, E. R.
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LIGHTNING protection ,TROPICAL climate ,CLIMATOLOGY ,THUNDERSTORMS - Abstract
The expression "lightning never strikes twice" is questioned in this paper because, among the randomness of lightning impacts, some spots are hit even more than twice year after year. This article introduces the recurrent lightning spots (RLS) concept, which are locations periodically impacted by cloud‐to‐ground lightning every consecutive year over a certain period. RLS are investigated in two regimes, with markedly different lightning climatology but similar orography, for 10 consecutive years: Catalonia (North East of Spain, Europe) and Barrancabermeja (North Central Colombia, South America). Results revealed 148 and 916 RLS in Catalonia and Barrancabermeja, respectively. RLS in both regions are typically found to be related to tall structures, mountain peaks, and steep terrain. The method allowed us to identify those tall towers and orographic relief frequently affected by lightning that are not detected with the mere computation of the ground flash density. In the case of Catalonia, some RLS are found offshore. Besides the scientific interest in understanding lightning, the new concept of RLS provides additional and valuable information applicable to lightning protection engineering. Plain Language Summary: The expression "lightning never strikes twice" is questioned in this paper because it shows that some spots are hit even more than twice: year after year. The RLSs (RLS) concept is presented, which are locations where lightning strike them periodically. The two regions of study with markedly different lightning climatology but similar orography are Catalonia (North East of Spain, Europe) and Barrancabermeja (in North Central Colombia, South America). RLS in both regions are typically found to be related to tall structures, mountain peaks and steep terrain. In the case of Catalonia, some RLS are found offshore. RLS new concept provides valuable information to lightning protection engineering. Key Points: Recurrent lightning spots (RLS) are targets with at least one cloud‐to‐ground lightning per year during a certain number of consecutive yearsIn Catalonia (Spain), 13% of the RLS are tall towers, 72% are mountainous peaks and 5% are offshore sitesThe method effectively finds tall structures affected by lightning in tropical climates [ABSTRACT FROM AUTHOR]
- Published
- 2024
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5. Fair Evaluation of Orientation‐Averaging Techniques in Light‐Scattering Simulations: Comment on "Evaluation of Higher‐Order Quadrature Schemes in Improving Computational Efficiency for Orientation‐Averaged Single‐Scattering Properties of Nonspherical Ice Particles" by Fenni et al
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Yurkin, Maxim A.
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PARTICLE symmetries ,SIMULATION methods & models ,COMPUTER programming ,LIGHT scattering - Abstract
In a recent paper Fenni et al. (2021, https://doi.org/10.1029/2020jd034172) compared the code MIDAS, based on the direct solution of the volume‐integral equation combined with advanced cubatures for orientation averaging, to the code DDSCAT, a state‐of‐the‐art implementation of the discrete dipole approximation. This comment highlights methodological issues in this comparison and shows that the quantitative claims of Fenni et al. (2021, https://doi.org/10.1029/2020jd034172), related to superiority of MIDAS over DDSCAT, are based on very specific test cases with respect to particle symmetries or initial orientation, as well as to the selected scattering quantity of interest. Thus, these claims are not expected to hold for other similar particles. Moreover, the detailed discussion of these issues is relevant for all light‐scattering simulation methods, except those allowing analytical orientation averaging. Thus, the comment constructs general guidelines for fair evaluation of orientation‐averaging techniques in a wide range of light‐scattering methods and computer codes. Plain Language Summary: The paper discusses several issues that appear when one is comparing different orientation‐averaging techniques (cubatures) in combination with the same or different light‐scattering simulation methods. Fair evaluation of cubature performance in realistic general scenarios is important both for practitioners (to choose the most efficient combination of the existing codes and cubatures) and for code developers (to set their priorities on the new features with the largest expected benefits). Unfortunately, the performance of the cubatures is complexly interwoven with the internals of the simulation methods and depends on specific test particles and computed scattering quantities. This questions the generality of conclusions in some previous publications. Based on this discussion, the paper ends with general guidelines for fair evaluation of cubatures, allowing future studies to arrive at general conclusions, so that they can be directly used by other researchers. Key Points: Quantitative conclusions of Fenni et al. (2021) are based on very specific test casesOrientation‐averaging techniques should be compared on non‐symmetric particles, and not with a special initial orientationAny comparison of simulated results should consider their uncertainties accounting for all sources of errors [ABSTRACT FROM AUTHOR]
- Published
- 2023
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6. Satellite Multi‐Angle Observations of Wildfire Smoke Plumes During the CalFiDE Field Campaign: Aerosol Plume Heights, Particle Property Evolution, and Aging Timescales.
- Author
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Noyes, K. T. Junghenn and Kahn, R. A.
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SMOKE plumes ,WILDFIRES ,AEROSOLS ,GEOPHYSICAL instruments ,SMOKE ,WILDFIRE prevention ,MEASURING instruments - Abstract
Wildfire‐related aircraft field campaigns frequently offer opportunities to validate remote‐sensing retrievals of aerosol properties and other quantities derived from satellite‐borne‐instrument observations. Satellite instruments often provide regional context‐imagery for more sparsely sampled aircraft and surface‐based measurements. However, aerosol amount, particle type, aerosol plume height and the associated wind vector products retrieved from the NASA Earth Observing System's Multi‐angle Imaging SpectroRadiometer (MISR) instrument have matured sufficiently that these quantities can also contribute substantially to a campaign data set, in regional context. This is especially useful when such measurements are not acquired at all from the suborbital platforms. During NOAA's California Fire Dynamics Experiment (CalFiDE), aircraft operations were coordinated with MISR overpasses on two occasions: for the Rum Creek fire on 30 August 2022, and for the Mosquito fire on 08 September. MISR‐retrieved aerosol properties show distinctly different patterns of black and brown smoke particle distributions and inferred plume evolution in the two cases. This paper presents the satellite‐retrieved results that complement the field observations, demonstrating what such measurements can offer, and contributing material for detailed fire dynamics and chemistry studies when combined with the CalFiDE suborbital observations and models in continuing studies. Plain Language Summary: A common use of aircraft field campaigns is to validate the radiances measured by space‐based instruments and the geophysical quantities derived from the satellite observations. However, satellite aerosol amount and properties derived from the NASA Earth Observing System's Multi‐angle Imaging SpectroRadiometer (MISR) instrument are sufficiently mature that they can also contribute directly to field‐campaign data sets. During NOAA's CalFiDE campaign is summer 2022, on two occasions the aircraft observed wildfire smoke plumes coordinated with MISR overpasses: for the Rum Creek fire on 30 August 2022, and for the Mosquito fire on 08 September. In addition to providing broad spatial context to the much more spatially limited aircraft measurements, the MISR results offer geometrically‐derived smoke‐plume height and plume‐level motion vectors from which smoke age can be estimated downwind along the plume. From MISR‐retrieved constraints on particle size, shape, and light‐absorption properties, the distribution of black and brown smoke can be inferred, along with the underlying processes responsible for plume‐particle evolution. This paper presents the satellite‐retrieved results that complement the suborbital data acquired for the CalFiDE campaign and associated modeling, for use in continuing studies of fire dynamics. Key Points: NASA's MISR multi‐angle imagery allows aerosol plume‐height, associated motion vector, and particle property retrievals from spaceTypically, field data are acquired to validate satellite data, but MISR data is mature enough to contribute directly to the CalFiDE campaignAircraft and MISR overflights were coordinated twice, yielding MISR aerosol context and detail for joint smoke‐plume dynamics and chemistry study [ABSTRACT FROM AUTHOR]
- Published
- 2024
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7. Characterizing Volcanic Ash Density and Its Implications on Settling Dynamics.
- Author
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Lau, Sing, Grainger, Roy G., and Taylor, Isabelle A.
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VOLCANIC ash, tuff, etc. ,VOLCANIC ash clouds ,DENSITY ,PARTICLE dynamics ,DENSITY currents - Abstract
Volcanic ash clouds are carefully monitored as they present a significant hazard to humans and aircraft. The primary tool for forecasting the transport of ash from a volcano is dispersion modeling. These models make a number of assumptions about the size, sphericity and density of the ash particles. Few studies have measured the density of ash particles or explored the impact that the assumption of ash density might have on the settling dynamics of ash particles. In this paper, the raw apparent density of 23 samples taken from 15 volcanoes are measured with gas pycnometry, and a negative linear relationship is found between the density and the silica content. For the basaltic ash samples, densities were measured for different particle sizes, showing that the density is approximately constant for particles smaller than 100 μm, beyond which it decreases with size. While this supports the current dispersion model used by the London Volcanic Ash Advisory Centre (VAAC), where the density is held at a constant (2.3 g cm−3), inputting the measured densities into a numerical simulation of settling velocity reveals a primary effect from the silica content changing this constant. The VAAC density overestimates ash removal times by up to 18%. These density variations, including those varying with size beyond 100 μm, also impact short‐range particle‐size distribution measurements and satellite retrievals of ash. Plain Language Summary: Volcanic ash clouds are carefully monitored as they present a significant hazard to humans and aircraft. Dispersion modeling is a primary tool used to forecast ash flows from volcanoes. These models make a number of assumptions about the size, sphericity (roundness) and density of the ash particles. Few studies have measured the density of ash particles or explored the impact that the assumption of ash density might have on the dispersion forecasts. In this paper, the density of 23 samples taken from 15 volcanoes are measured, and a negative linear relationship is found between the density and the silica content. For the basaltic ash samples (the most common type of ash), densities were measured for different particle sizes, showing that the density is approximately constant for particles smaller than 100 μm, beyond which it decreases with size. This supports the London Volcanic Ash Advisory Centre keeping density constant in their current model, but in fact this constant changes with silica content, leading to an overestimation of ash removal times by up to 18%. These density deviations also impact short‐range particle‐size distribution measurements and satellite retrievals of ash. Key Points: The density of volcanic ash is measured as a function of particle size for a range of eruptionsSilica content and particle size negatively correlate with densityThe density of particles smaller than 100 μm is approximately constant but is dependent on silica content [ABSTRACT FROM AUTHOR]
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- 2024
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8. Long‐Term Alpine Precipitation Reconstruction (LAPrec): A Gridded Monthly Data Set Dating Back to 1871.
- Author
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Isotta, F. A., Chimani, B., Hiebl, J., and Frei, C.
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BUILDING repair ,PRECIPITATION gauges ,DATA libraries ,TIME series analysis ,TREND analysis ,NINETEENTH century - Abstract
Spatial climate data sets that extend back in time over many decades are an important resource for climate monitoring. The long‐term consistency of such data sets is, however, compromised by changes in the measurement systems over time. In this paper, we introduce a data set of monthly precipitation on a 5‐km grid over the European Alps that extends back to the late 19th century. In deriving the "long‐term Alpine precipitation reconstruction" (LAPrec), special care is taken of variations in the station network, in order for the data set to satisfy high standards in long‐term consistency. LAPrec builds on a reconstruction method that integrates the available information in two portions: The first is a set of high‐quality homogenized station series, taken from the HISTALP data archive, covering the entire period almost continuously. The second is a high‐resolution gridded precipitation analysis, taken from the "Alpine Precipitation Grid Data Set," constructed from thousands of rain‐gauges but covering a few decades only. We demonstrate how the reconstruction approach successfully introduces mesoscale structures that are not resolved by the available long‐term station series, more plausibly so than a predecessor data set using conventional interpolation. We also illustrate that LAPrec reveals long‐term precipitation trends that are spatially more consistent and more detailed than the trends in popular climate monitoring data sets. Over the period 1871–2017 a statistically significant increase is found in winter over the northern parts of the Alps (1%–2% per 10 years). LAPrec is available in two versions (back until 1871 and 1901 respectively) from the Copernicus climate data store. Plain Language Summary: Data sets extending back in time over many decades are an important resource for climate monitoring. In this paper, we introduce a data set on a regular grid of monthly precipitation over the European Alps that extends back to 1871. In deriving the "long‐term Alpine precipitation reconstruction" (LAPrec), special care is taken to keep the station network constant and make use of high‐quality homogenized time series, in order for the data set to be as consistent as possible over time. LAPrec builds on two sources of information: The first is a set of high‐quality station series from the HISTALP data archive, covering the entire period almost continuously. The second is a high‐resolution gridded precipitation analysis, the "Alpine Precipitation Grid Data Set," constructed from thousands of rain‐gauges but covering a few decades only. We demonstrate how this approach successfully introduces details that are not resolved by the available long‐term station series. We also illustrate that LAPrec reveals long‐term precipitation trends that are spatially more consistent and detailed than the trends in popular climate monitoring data sets. Over the period 1871–2017 a statistically significant increase in winter precipitation is found over the northern parts of the Alps. LAPrec is available from the Copernicus climate data store. Key Points: Long‐term spatial analyses of precipitation in the European Alps since 1871For applications such as climate monitoring and trend analysis, the data set meets high standards in long‐term consistency and homogeneityLong‐term Alpine precipitation reconstruction detects a significant trend in winter precipitation over the northern part of the Alps in the period starting from 1871 [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
9. Changes in Moisture Sources of Atmospheric Rivers Landfalling the Iberian Peninsula With WRF‐FLEXPART.
- Author
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Fernández‐Alvarez, J. C., Pérez‐Alarcón, A., Eiras‐Barca, J., Ramos, A. M., Rahimi‐Esfarjani, S., Nieto, R., and Gimeno, L.
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ATMOSPHERIC rivers ,HUMIDITY ,ATMOSPHERIC boundary layer ,ATMOSPHERIC models ,PENINSULAS - Abstract
This paper makes use of a combination of FLEXPART‐WRF simulations forced with ERA5 and the CESM2 model—incorporated in the CMIP6 project—to infer a series of changes over the present century in the behavior of the landfalling atmospheric rivers (ARs) arriving to the Iberian Peninsula. In addition, future changes in the intensity and position of their main moisture sources are studied. In overall terms, there is a noticeable increase in the amount of moisture transported by ARs in the study region, particularly accentuated by the end of the century. However, no significant changes in the number of events are observed. A northward shift of both the mean position of the ARs as well as their main sources of moisture is also detected, particularly for the end of the century, and in the summer and fall months. In relation to the latter, an increase in the contribution of moisture contribution is also observed, quantitatively compatible with Clausius‐Clapeyron amplification. Plain Language Summary: This paper makes use of a combination of simulations forced with reanalysis data and a climate model to infer a series of changes over the present century in the behavior of the landfalling atmospheric river—ARs, regions of intense moisture transport located in the lower layers of the atmosphere—arriving at the Iberian Peninsula. In addition, future changes in the intensity and position of their main moisture sources are studied. In overall terms, there is a noticeable increase in the amount of moisture transported by ARs in the study region, particularly accentuated by the end of the century. However, no significant changes in the number of events are observed. A northward shift of both the mean position of the ARs as well as their main sources of moisture is also detected, particularly for the end of the century, and in the summer and fall months. In relation to the latter, an increase in the contribution of moisture contribution is also observed, in a ratio similar to that expected. Key Points: FLEXPART‐WRF forced with CESM2 model has been able to reproduce the historical conditions of Atmospheric River over the Iberian PeninsulaA northward shift of the main source regions is projected, notable in summer and fall and particularly by the end of the centuryGradual strengthening in the intensity of Atmospheric Rivers is expected, observable from an increase in the amount of moisture transported [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
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10. Upward Leaders Initiated From Instrumented Lightning Rods During the Approach of a Downward Leader in a Cloud‐To‐Ground Flash.
- Author
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Saba, Marcelo M. F., Lauria, Paola B., Schumann, Carina, Silva, José Claudio de O., and Mantovani, Felipe de L.
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LIGHTNING ,LIGHTNING protection ,CHARGE measurement ,ELECTRIC fields ,DENSITY currents - Abstract
In this paper we analyze electric‐field and current measurements of upward leaders induced by a downward negative lightning flash that struck a residential building. The attachment process was recorded by two high‐speed cameras running at 37,800 and 70,000 images per second and the current measured in two lightning rods. Differently from previous works, here we show, for the first time, current measurements of multiple upward leaders that after initiation propagate to connect the negative downward moving leader. At the beginning of the propagation of the leaders that initiate on the instrumented lightning rods, current pulses appear superimposed to a steadily increasing DC current. The upward leader current pulses increase with the approach of the downward leader and are not synchronized but present an alternating pattern. All 2D leader speeds are approximately constant. The upward leaders are slower than the downward leader speed. The average time interval between current pulses in upward leaders is close to the interstep time interval found by optical or electric field sensors for negative cloud‐to‐ground stepped leaders. The upward leaders respond to different downward propagating branches and, as the branches alternate in propagation and intensity, so do the leaders accordingly. Right before the attachment process the alternating pattern of the leaders ceases, all downward leader branches intensify, and consequently upward leaders synchronize and pulse together. The average linear densities for upward leaders (49 and 82 μC/m) were obtained for the first time for natural lightning. Plain Language Summary: The effectiveness of a lightning protection system depends on its efficiency to intercept the down coming leader of a cloud‐to‐ground lightning flash. The interception is usually done by an upward connecting leader that initiates from grounded structures, humans, or living beings that protrude from nearby ground. The understanding of the upward connecting leader and of the attachment process with the downward leader plays an important role in the determination of the zone of protection and therefore in the improvement of a lightning protection system. Unconnected upward leaders, that is, upward leaders that fail to connect the downward leader, are also of great importance in lightning protection. They can be large enough to cause damage to equipment vulnerable to sparks or induced currents, and enough to injure people from who it initiates. In this paper we analyze electric‐field, speed, and current measurements of upward leaders induced by a downward negative lightning flash that struck a residential building. The attachment process was simultaneously recorded by two high‐speed cameras, an electric‐field sensor, and current sensors installed on two lightning rods. Differently from previous works we show, for the first time, current measurements of multiple upward leaders induced by the negative downward moving leader. Key Points: Current and charge density measurements of two upward leaders induced by the same downward leaderUpward leaders alternate their progression during initial propagationCurrent pulses of upward leaders increase intensity and synchronize right before attachment [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
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