Showing papers on "Thunderstorm published in 2011"
TL;DR: In this paper, a radar-based climatology of 91 unique summertime (May 2000-August 2009) thunderstorm cases was examined over the Indianapolis, Indiana, urban area.
Abstract: A radar-based climatology of 91 unique summertime (May 2000–August 2009) thunderstorm cases was examined over the Indianapolis, Indiana, urban area. The study hypothesis is that urban regions alter the intensity and composition/structure of approaching thunderstorms because of land surface heterogeneity. Storm characteristics were studied over the Indianapolis region and four peripheral rural counties approximately 120 km away from the urban center. Using radar imagery, the time of event, changes in storm structure (splitting, initiation, intensification, and dissipation), synoptic setting, orientation, and motion were studied. It was found that more than 60% of storms changed structure over the Indianapolis area as compared with only 25% over the rural regions. Furthermore, daytime convection was most likely to be affected, with 71% of storms changing structure as compared with only 42% at night. Analysis of radar imagery indicated that storms split closer to the upwind urban region and merge aga...
227 citations
TL;DR: In this article, the authors examined the utility of the Geostationary Lightning Mapper (GLM) to operational meteorology in anticipation of severe convective weather on a hemispheric scale.
Abstract: Many studies over the past several decades have attempted to correlate trends in lightning (e.g., rates, polarity) to severe weather occurrence. These studies mainly used cloud-to-ground (CG) lightning information due to the ease of data availability, high detection efficiency, and broad coverage across the United States, with somewhat inconclusiveresults.Conversely, it has been demonstrated that trendsin total lightning aremorerobustlycorrelatedtosevereweatheroccurrence,withrapidincreasesintotallightningobserved10s of minutes prior to the onset of severe weather. Unfortunately, total lightning observations are not as numerous, or available over the same areal coverage domain, as provided by CG networks. Relatively few studieshaveexamined concurrent trendsin bothtotalandCG lightningwithinthesameseverethunderstorm, or even large sets of thunderstorms using an objective lightning jump algorithm. Multiple studies have shown thatthetotalflashraterapidlyincreasespriortotheonsetofsevereweather.Whatisuntestedwithinthesame framework is the use of CG information to perform the same task. Herein, total and CG lightning trends for 711 thunderstorms occurring in four regions of the country were examined to demonstrate the increased utilitythattotallightningprovides overCGlightning,specifically withintheframeworkofdevelopingauseful lightning-based severe weather warning decision support tool. Results indicate that while both lightning datasets demonstrate the presence of increased lightning activity prior to the onset of severe weather, the use oftotal lightningtrendswasmore effectivethanCG trends[probability ofdetection(POD),79% versus66%; false alarm rate (FAR), 36% versus 53%; critical success index (CSI), 55% versus 38%; Heidke skill score (HSS), 0.71 versus 0.55]. Moreover, 40% of false alarms associated with total lightning, and 16% of false alarms with CG lightning trends, occurred when a lightning jump associated with a severe weather ‘‘warning’’ was already in effect. If these false alarms are removed, the FAR drops from 36% to 22% for total lightning and from 53% to 44% for CG lightning. Importantly, average lead times prior to severe weather occurrence werehigherusingtotallightningascomparedwithCGlightning(20.65versus13.54 min).Theultimategoalof this study was to demonstrate the increased utility of total lightning information that the Geostationary Lightning Mapper (GLM) will provide to operational meteorology in anticipation of severe convective weather on a hemispheric scale once Geostationary Operational Environmental Satellite-R (GOES-R) is deployed in the next decade.
194 citations
TL;DR: This paper performed three-dimensional supercell simulations using the two-moment bulk microphysics schemes of Morrison and Milbrandt-Yau in the Weather Research and Forecasting (WRF) model.
Abstract: Idealized three-dimensional supercell simulations were performed using the two-moment bulk microphysics schemes of Morrison and Milbrandt–Yau in the Weather Research and Forecasting (WRF) model. Despite general similarities in these schemes, the simulations were found to produce distinct differences in storm structure, precipitation, and cold pool strength. In particular, the Morrison scheme produced much higher surface precipitation rates and a stronger cold pool, especially in the early stages of storm development. A series of sensitivity experiments was conducted to identify the primary differences between the two schemes that resulted in the large discrepancies in the simulations.Different approaches in treating graupel and hail were found to be responsible for many of the key differences between the baseline simulations. The inclusion of hail in the baseline simulation using the Milbrant–Yau scheme with two rimed-ice categories (graupel and hail) had little impact, and therefore resulted in a...
174 citations
TL;DR: In this paper, the authors explored the potential for new forms of forecast guidance using output from a series of convection-allowing NWP models (CAMs) generated on a daily basis during the spring of 2008.
Abstract: With the advent of convection-allowing NWP models (CAMs) comes the potential for new forms of forecast guidance. While CAMs lack the required resolution to simulate many severe phenomena associated with convection (e.g., large hail, downburst winds, and tornadoes), they can still provide unique guidance for the occurrence of these phenomena if “extreme” patterns of behavior in simulated storms are strongly correlated with observed severe phenomena. This concept is explored using output from a series of CAM forecasts generated on a daily basis during the spring of 2008. This output is mined for the presence of extreme values of updraft helicity (UH), a diagnostic field used to identify supercellular storms. Extreme values of the UH field are flagged as simulated “surrogate” severe weather reports and the spatial correspondence between these surrogate reports and actual observed severe reports is determined. In addition, probabilistic forecasts [surrogate severe probabilistic forecasts (SSPFs)] are ...
128 citations
TL;DR: Observations of a storm at northern latitudes in the peak of a weak westward jet during the beginning of northern springtime, in accord with the seasonal cycle but earlier than expected, and triggered a planetary-scale disturbance that circled Saturn but did not significantly alter the ambient zonal winds.
Abstract: Six Great White Spot (GWS) events have been observed in the atmosphere of Saturn since 1876. These giant convective storms occur roughly once every Saturnian year (equal to 29.5 Earth years). The sixth GWS erupted in December 2010 and has been the subject of intense observation. Two papers in this issue present the details of some of these observations. Sanchez-Lavega et al. report that the storm developed at northern latitudes in the peak of a weak westward jet during early northern springtime. The storm head moved faster than the jet and triggered a disturbance that circled the planet. Numerical simulations show that Saturn's winds extend without decay deep down into the weather layer. Fischer et al. report that the storm reached a width of 10,000 kilometres within three weeks. Its lightning flash rates are an order of magnitude greater than those seen in previous storms, peaking at more than 10 flashes per second. Convective storms occur regularly in Saturn’s atmosphere1,2,3,4. Huge storms known as Great White Spots, which are ten times larger than the regular storms, are rarer and occur about once per Saturnian year (29.5 Earth years). Current models propose that the outbreak of a Great White Spot is due to moist convection induced by water5,6. However, the generation of the global disturbance and its effect on Saturn’s permanent winds1,7 have hitherto been unconstrained8 by data, because there was insufficient spatial resolution and temporal sampling9,10,11 to infer the dynamics of Saturn’s weather layer (the layer in the troposphere where the cloud forms). Theoretically, it has been suggested that this phenomenon is seasonally controlled5,9,10. Here we report observations of a storm at northern latitudes in the peak of a weak westward jet during the beginning of northern springtime, in accord with the seasonal cycle but earlier than expected. The storm head moved faster than the jet, was active during the two-month observation period, and triggered a planetary-scale disturbance that circled Saturn but did not significantly alter the ambient zonal winds. Numerical simulations of the phenomenon show that, as on Jupiter12, Saturn’s winds extend without decay deep down into the weather layer, at least to the water-cloud base at pressures of 10–12 bar, which is much deeper than solar radiation penetrates.
121 citations
TL;DR: Observations of a giant thunderstorm at planetocentric latitude 35° north that reached a latitudinal extension of 10,000 kilometres about three weeks after it started in early December 2010, which developed an elongated eastward tail with additional but weaker storm cells that wrapped around the whole planet by February 2011.
Abstract: Lightning discharges in Saturn’s atmosphere emit radio waves with intensities about 10,000 times stronger than those of their terrestrial counterparts. These radio waves are the characteristic features of lightning from thunderstorms on Saturn, which last for days to months. Convective storms about 2,000 kilometres in size have been observed in recent years at planetocentric latitude 35° south (corresponding to a planetographic latitude of 41° south). Here we report observations of a giant thunderstorm at planetocentric latitude 35° north that reached a latitudinal extension of 10,000 kilometres—comparable in size to a ‘Great White Spot’—about three weeks after it started in early December 2010. The visible plume consists of high-altitude clouds that overshoot the outermost ammonia cloud layer owing to strong vertical convection, as is typical for thunderstorms. The flash rates of this storm are about an order of magnitude higher than previous ones, and peak rates larger than ten per second were recorded. This main storm developed an elongated eastward tail with additional but weaker storm cells that wrapped around the whole planet by February 2011. Unlike storms on Earth, the total power of this storm is comparable to Saturn’s total emitted power. The appearance of such storms in the northern hemisphere could be related to the change of seasons, given that Saturn experienced vernal equinox in August 2009.
110 citations
TL;DR: In this paper, a thunderstorm was initiated within a line of cumulus clouds which formed parallel to the crest of the Black Forest mountains during the Intensive Observation Period (IOP) 8b of the Convective and Orographically-induced Precipitation Study (COPS).
Abstract: In the afternoon of 15 July 2007, a thunderstorm was initiated within a line of cumulus clouds which formed parallel to the crest of the Black Forest mountains during the Intensive Observation Period (IOP) 8b of the Convective and Orographically-induced Precipitation Study (COPS). This paper extends the analysis of processes that led to convection initiation (CI), i.e. the transition from shallow to deep convection, on this day with the data from several COPS instruments that have not been considered in previous studies. In particular, the boundary-layer structure, lids and the water-vapour field in the pre-convective environment of the event are discussed. For this purpose, we investigated measurements of water-vapour lidars, temperature lidars and wind lidars, profiles from radiosondes, in situ aircraft data and gridded data of weather stations as well as GPS integrated-water-vapour data and satellite imagery. Thermally driven circulation systems formed over both the Black Forest and the Vosges mountain ranges which resulted in local convergence zones. These superimposed with the large-scale convergence in the Black Forest area. In the presence of sufficient moisture and updraught, clouds formed close to the mountain crests. The related latent-heat release allowed larger thermals to be produced, which may have had a positive feedback on stabilizing these convergence zones as a whole. We believe that differences in the moisture field explain why convection remained shallow and sparse over the Vosges mountains because these differences were responsible for differences in convective inhibition (CIN). The stationary location of the convergence zone over the southern Black Forest was probably decisive for CI because it constantly transported sensible and latent heat into the area in which CI took place.
101 citations
TL;DR: In this paper, the authors combined analyses of high-altitude aircraft observations of electrified clouds with diurnal lightning statistics from the Lightning Imaging Sensor (LIS) and Optical Transient Detector (OTD) carried aboard low-Earth-orbiting satellites to reproduce the diurnal variation in the global electric circuit.
Abstract: [1] We have combined analyses of high-altitude aircraft observations of electrified clouds with diurnal lightning statistics from the Lightning Imaging Sensor (LIS) and Optical Transient Detector (OTD) that are carried aboard low-Earth-orbiting satellites to reproduce the diurnal variation in the global electric circuit. Using basic assumptions about the mean storm currents as a function of flash rate and location (i.e., land or ocean) and the global electric circuit, our estimate of the current in the global electric circuit matches the Carnegie curve diurnal variation to within 4% for all but two short periods of time, in which the difference was 11% in one time period (0430 UTC) and 6% in the second period (1830 UTC). This excellent agreement with the Carnegie curve was obtained without any tuning or adjustment of the satellite or aircraft data. We assume that (1) the mean values for current and flash rates in the aircraft storm overflight data set (1.7 A and 0.8 flashes min−1 for oceanic thunderstorms, 1.0 A and 2.2 flashes min−1 for land thunderstorms, 0.41 A for oceanic electrified shower clouds (i.e., electrified but no lightning detected), and 0.13 A for land electrified shower clouds) and (2) the diurnal variations in lightning rates over land and ocean found in the satellite data set are universally applicable. Mean contributions to the global electric circuit from land and ocean thunderstorms are 1.1 kA (land) and 0.7 kA (ocean). Contributions to the global electric circuit from electrified shower clouds are 0.22 kA for ocean storms and 0.04 kA for land storms. The mean total conduction current for the global electric circuit is 2.0 kA. The means that for the number of storms contributing to the global electric circuit, 1100 are land storms with lightning, 530 are ocean storms without lightning, 390 are ocean storms with lightning, and 330 are land storms without lightning. A closer fit to the Carnegie curve is possible if the contributions from electrified shower clouds are increased by a factor of 3 or 4.
97 citations
TL;DR: In this article, satellite observations are used to understand the timing, duration, and frequency of deep convection in equatorial Africa, a region with some of the most intense thunderstorms.
Abstract: Long-term statistics of organized convection are vital to improved understanding of the hydrologic cycle at various scales. Satellite observations are used to understand the timing, duration, and frequency of deep convection in equatorial Africa, a region with some of the most intense thunderstorms. Yet little has been published about the propagation characteristics of mesoscale convection in that region. Diurnal, subseasonal, and seasonal cycles of cold cloud (proxy for convective precipitation) are examined on a continental scale. Organized deep convection consists of coherent structures that are characteristic of systems propagating under a broad range of atmospheric conditions. Convection is triggered by heating of elevated terrain, sea/land breezes, and lake breezes. Coherent episodes of convection result from regeneration of convection through multiple diurnal cycles while propagating westward. They have an average 17.6-h duration and 673-km span; most have zonal phase speeds of 8–16 m s−1.P...
88 citations
TL;DR: In this article, an attempt has been made to assess the skill of various indices and parameters and to propose suitable threshold values in forecasting the occurrence of thunderstorm activity at Kolkata.
Abstract: The pre-monsoon convective atmosphere over Kolkata (22.52°N, 88.37°E) during STORM field phase 2006–2008 is investigated using 12 UTC radiosonde data and thermodynamic indices. In the present study, an attempt has been made to assess the skill of various indices and parameters and to propose suitable threshold values in forecasting the occurrence of thunderstorm activity at Kolkata. The thermodynamic indices and parameters used in the present study are lifted index (LI), K index (KI), severe weather threat index (SWEAT), total totals index (TTI), convective available potential energy (CAPE), deep convection index (DCI), humidity index (HI), Boyden index (BI), dew point temperature at 850 hpa (DEW), relative humidity at 700 hpa (RH), and bulk Richardson number (BRN). Validation of the suggested threshold values of indices was conducted on the days of thunderstorm activity. It was found that one index alone cannot predict the occurrence of thunderstorm over Kolkata region. The present study suggests that the indices with highest skill for thunderstorm prediction are KI, DCI, SWEAT, DEW, HI, RH, LI, TTI, while the prediction efficiency is poor for CAPE, BRN, and BI. Observed values of these indices also reveal that scattered, multi-cellular thunderstorms are possible over Kolkata during pre-monsoon months.
86 citations
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TL;DR: A measurement tool called ThunderPing is designed and deployed that measures the connectivity of residential Inter- net hosts before, during, and after forecast periods of severe weather, and finds that compared to clear weather, failures are four times as likely during thunderstorms and two times aslikely during rain.
Abstract: Residential Internet connections are susceptible to weather-caused outages: Lightning and wind cause local power failures, direct lightning strikes destroy equipment, and water in the atmosphere degrades satellite links. Outages caused by severe events such as fires and undersea cable cuts are often reported upon by operators and studied by researchers. In contrast, outages cause by ordinary weather are typically limited in scope, and because of their small scale, there has not been comparable effort to understand how weather affects everyday last-mile Internet connectivity. We design and deploy a measurement tool called ThunderPing that measures the connectivity of residential Inter- net hosts before, during, and after forecast periods of severe weather. ThunderPing uses weather alerts from the US National Weather Service to choose a set of residential host addresses to ping from several vantage points on the Internet. We then process this ping data to determine when hosts lose connectivity, completely or partially, and categorize whether these failures occur during periods of severe weather or when the skies are clear. In our preliminary results, we find that compared to clear weather, failures are four times as likely during thunderstorms and two times as likely during rain. We also find that the duration of weather induced outages is relatively small for a satellite provider we focused on.
TL;DR: In this article, the first spring storm season after the deployment of four radars in the CASA Integrated Project-1 (IP-1) network in southwest Oklahoma, a tornadic mesoscale convective system (MCS) was captured by CASA and surrounding Weather Surveillance Radars-1988 Doppler (WSR-88Ds) on 8-9 May 2007.
Abstract: One of the goals of the National Science Foundation Engineering Research Center (ERC) for Collaborative Adaptive Sensing of the Atmosphere (CASA) is to improve storm-scale numerical weather prediction (NWP) by collecting data with a dense X-band radar network that provides high-resolution low-level coverage, and by assimilating such data into NWP models. During the first spring storm season after the deployment of four radars in the CASA Integrated Project-1 (IP-1) network in southwest Oklahoma, a tornadic mesoscale convective system (MCS) was captured by CASA and surrounding Weather Surveillance Radars-1988 Doppler (WSR-88Ds) on 8–9 May 2007. The MCS moved across northwest Texas and western and central Oklahoma; two tornadoes rated as category 1 on the enhanced Fujita scale (EF-1) and one tornado of EF-0 intensity were reported during the event, just to the north of the IP-1 network. This was the first tornadic convective system observed by CASA.To quantify the impacts of CASA radar data in storm...
TL;DR: In this article, the authors identify a migrating source of high energy radiation, lasting for several minutes, attributed to thunderstorm activities through the observations of radiation, atmospheric electric field, and meteorological radar echoes at several points.
Abstract: [1] We identify a migrating source of high energy radiation, lasting for several minutes, attributed to thunderstorm activities through the observations of radiation, atmospheric electric field, and meteorological radar echoes at several points. Our findings indicate that the energetic radiation is emitted continuously from a downward hemispherical surface without lightning, the bottom of which is about 300 m above sea level, and this source of radiation moves from north to south above the observation site at the speed of about 7 m/s. The radiation source probably moves along with the negatively charged region of the cloud at the height of around 1 km, because the estimated migration of the radiation source is consistent with the observed movement of atmospheric electric field variation between ground-based observation sites and with the wind speed and direction at about 1 km altitude. This movement implies that the intensive electric field produced by the charged region in the thundercloud generates a radiation source. In addition, our results suggest that the low altitude of radiation source is related to no lightning activity during the energetic radiation emission.
TL;DR: In this paper, the role of energetic charged particles (including cosmic rays) on cloud formation and their effect on climate is examined, and it is considered that the cosmic ray-cloud cover hypothesis is not supported by presently available data and further investigations (during Forbush decreases and at other times) should be analyzed to further examine the hypothesis.
Abstract: The physics of solar forcing of the climate and long term climate change is summarized, and the role of energetic charged particles (including cosmic rays) on cloud formation and their effect on climate is examined. It is considered that the cosmic ray-cloud cover hypothesis is not supported by presently available data and further investigations (during Forbush decreases and at other times) should be analyzed to further examine the hypothesis. Another player in climate is lightning through the production of NOx; this greenhouse gas, water vapour in the troposphere (and stratosphere) and carbon dioxide influence the global temperature through different processes. The enhancement of aerosol concentrations and their distribution in the troposphere also affect the climate and may result in enhanced lightning activity. Finally, the roles of atmospheric conductivity on the electrical activity of thunderstorms and lightning discharges in relation to climate are discussed.
TL;DR: A unique and broad database of severe thunderstorm reports has been constructed for the Australian region for 2003-2010 from observer reports of hailstones, winds in excess of 90 km h-1 and, less frequently, tornadoes.
Abstract: Severe thunderstorms can present a significant threat to life and property in Australia. A unique and broad database of severe thunderstorm reports has been constructed for the Australian region for 2003-2010 from observer reports of hailstones, winds in excess of 90 km h-1 and, less frequently, tornadoes. Based on this database, a climatology of atmospheric environments associated with the occurrence of severe thunderstorms in Australia was developed using pseudo-proximity soundings from the MesoLAPS numerical weather prediction model simulations. Observed soundings have been used to verify derived soundings from MesoLAPS simulations, with a reasonable performance over much of the continent. Proximity rawinsonde soundings from the MesoLAPS simulations were identified for each of the severe thunderstorm reports to develop the climatology of environments. This climatology was then used to derive discriminants between environments with an increased likelihood of severe thunderstorm occurrence and other thunderstorm environments. This appears to be the best way to produce a long-term climatology of severe thunderstorm environment occurrence in a sparsely populated continent without considering the complex problem of initiation.
TL;DR: In this article, the effects of idealized two-dimensional terrain on a cyclonically rotating supercell thunderstorm are studied with a numerical model, and it is shown that there is a tendency for the simulated supercells to weaken in terms of the intensities of their updrafts and mesocyclones in the lee of terrain features where downsloping is present.
TL;DR: In this article, the authors investigated the physical processes involved in the development of thunderstorms over southwestern Amazon by hypothesizing causalities for the observed cloud-to-ground lightning variability and the local environmental characteristics.
Abstract: [1] This study investigated the physical processes involved in the development of thunderstorms over southwestern Amazon by hypothesizing causalities for the observed cloud-to-ground lightning variability and the local environmental characteristics. Southwestern Amazon experiences every year a large variety of environmental factors, such as the gradual increase in atmospheric moisture, extremely high pollution due to biomass burning, and intense deforestation, which directly affects cloud development by differential surface energy partition. In the end of the dry period it was observed higher percentages of positive cloud-to-ground (+CG) lightning due to a relative increase in +CG dominated thunderstorms (positive thunderstorms). Positive (negative) thunderstorms initiated preferentially over deforested (forest) areas with higher (lower) cloud base heights, shallower (deeper) warm cloud depths, and higher (lower) convective potential available energy. These features characterized the positive (negative) thunderstorms as deeper (relatively shallower) clouds, stronger (relatively weaker) updrafts with enhanced (decreased) mixed and cold vertically integrated liquid. No significant difference between thunderstorms (negative and positive) and nonthunderstorms were observed in terms of atmospheric pollution, once the atmosphere was overwhelmed by pollution leading to an updraft-limited regime. However, in the wet season both negative and positive thunderstorms occurred during periods of relatively higher aerosol concentration and differentiated size distributions, suggesting an aerosol-limited regime where cloud electrification could be dependent on the aerosol concentration to suppress the warm and enhance the ice phase. The suggested causalities are consistent with the invoked hypotheses, but they are not observed facts; they are just hypotheses based on plausible physical mechanisms.
TL;DR: In this paper, the authors used the ZEUS ground-based VLF lightning detection network and the Warning Decision Support System-Integrated Information (WDSS-II) software to perform now-casting simulations using 1-year of lightning data over the Mediterranean area.
TL;DR: In this paper, the main weather systems and resultant wind systems responsible for dust entrainment and transport in the lower Lake Eyre were quantified using 2.5 years of meteorological observations and mean sea level synoptic analyses.
TL;DR: In this paper, the authors employed a radar-based morphology classification system that delineates storm type based on an organizational continuum, including unorganized cellular, quasi-organized cellular (either a cluster of cells or a broken line of cells), organized cellular (supercells and supercells embedded in an organized linear system), and organized linear (either squall lines or bow echoes).
Abstract: There are still hundreds of casualties produced by thunderstorm hazards each year in the United States despite the many recent advances in prediction and mitigation of the effects of convective storms. Of the four most common thunderstorm hazards (wind, hail, flooding, and lightning), convective winds (tornadic and nontornadic) remain one of the most dangerous threats to life and property. Using thunderstorm fatality and Weather Surveillance Radar-1988 Doppler (WSR-88D) data, this research illustrates a spatial and temporal analysis of the storm morphological characteristics, or convective mode, of all fatal tornadic and nontornadic convectivewind eventsfrom 1998 to 2007.The investigation employs a radar-based morphology classification system that delineates storm type based on an organizational continuum, including unorganized cellular, quasi-organized cellular (either a cluster of cells or a broken line of cells), organized cellular (supercells and supercells embedded in an organized linear system), and organized linear (either squall lines or bow echoes). Results illustratethat over90% of the 634 recorded tornadodeaths were associated with supercells, with 78% of the deaths due to isolated tornadic supercells and 12% linked to tornadic supercells embedded within an organized linear convective system. The morphologies responsible for the 191 nontornadic convective wind fatalities vary substantially, with bow echoes (24%), squall lines (19%), and clusters of cells (19%) the most prominent convective modes producing fatalities. Unorganized and quasi-organized convection accounted for nearly half (45%) of all nontornadic convective wind fatalities. Over half of all fatal tornadoes (53%) occurredbetween0000and0600UTC,andmost(59%)fatalitiesfromnontornadicconvectivewindsoccurred in the afternoon between 1800 and 0000 UTC. Two corridors of nontornadic convective wind fatalities were present:thelowerGreatLakesregionandthemid-South.Tornadofatalitiesweregreatestinazoneextending from southeastern Missouri, through western Tennessee, northeastern Arkansas, Mississippi, Alabama, and Georgia. The methods employed and results found in this study are directly applicable in the further development of storm classification schemesand provide forecasters andemergency managers with information to assist in the creation and implementation of new convective wind mitigation strategies.
TL;DR: In this article, the authors used polarimetric radar measurements over regularly occurring thunderstorms over the islands north of Darwin, Australia to test if aerosol contributions to the probability distributions of the drop size distribution parameters (median volume diameter and normalized intercept parameter) are detectable.
Abstract: Rain drop size distributions retrieved from polarimetric radar measurements over regularly occurring thunderstorms over the islands north of Darwin, Australia, are used to test if aerosol contributions to the probability distributions of the drop size distribution parameters (median volume diameter and normalized intercept parameter) are detectable. The observations reported herein are such that differences in cloud properties arising from thermodynamic differences are minimized but even so may be a factor. However, there is a clear signature that high aerosol concentrations are correlated with smaller number concentrations and larger drops. This may be associated with enhanced ice multiplication processes for low aerosol concentration storms or other processes such as invigoration of the updrafts.
TL;DR: In this article, the first high-time resolution 2D images of X-ray emissions from lightning were obtained using a pinhole-type camera, located 44 m from a rocket-and-wire-triggered lightning.
Abstract: [1] We present the first high-time resolution two-dimensional images of X-ray emissions from lightning. The images were recorded at a rate of 10 million per second using a new pinhole-type camera, located 44 m from rocket-and-wire-triggered lightning. We report observations of two dart leaders, one in each of two lightning flashes triggered during the summer of 2010 in north-central Florida. In both events, as the dart leader approached the ground, the X-ray source was also seen to descend along the previous lightning channel. For the second event, the X-ray source exhibited a downward speed of 4.5 × 107 m/s, in agreement with independent dE/dt time-of-arrival (TOA) measurements of the speed of the dart leader front, demonstrating that the dart leader front was the source of the X-ray emission. The camera also recorded bursts of MeV gamma rays originating from the dart leader and/or the ground attachment process of the leader. Overall, these results provide new insight into the production of energetic radiation and the propagation and attachment of lightning, all of which remain poorly understood.
TL;DR: In this article, the chemical composition in the outflow of large mesoscale convective systems (MCS) was investigated using the German research aircraft Falcon based in Ouagadougou (Burkina Faso) and the Lightning Location Network (LINET) set up in Northern Benin.
Abstract: . During the "African Monsoon Multidisciplinary Analysis" (AMMA) field phase in August 2006, a variety of measurements focusing on deep convection were performed over West Africa. The German research aircraft Falcon based in Ouagadougou (Burkina Faso) investigated the chemical composition in the outflow of large mesoscale convective systems (MCS). Here we analyse two different types of MCS originating north and south of the intertropical convergence zone (ITCZ, ~10° N), respectively. In addition to the airborne trace gas measurements, stroke measurements from the Lightning Location Network (LINET), set up in Northern Benin, are analysed. The main focus of the present study is (1) to analyse the trace gas composition (CO, O3, NO, NOx, NOy, and HCHO) in the convective outflow as a function of distance from the convective core, (2) to investigate how different trace gas compositions in the boundary layer (BL) and ambient air may influence the O3 concentration in the convective outflow, and (3) to estimate the rate of lightning-produced nitrogen oxides per flash in selected thunderstorms and compare it to our previous results for the tropics. The MCS outflow was probed at different altitudes (~10–12 km) and distances from the convective core (
TL;DR: In this paper, the authors analyzed the processes driving deep convection over complex terrain and showed that the interaction of the CI processes on multiple scales locally leads to either deep convective and severe storms or calm weather.
Abstract: The ‘Convective and Orographically-induced Precipitation Study’ (COPS) analyses the processes driving deep convection over complex terrain. Convection initiation (CI) is mainly not only expressed by a single process, but by a variety of them, which interact on different scales in time and space and finally can lead to deep convection. A study of such a case over inhomogeneous terrain is presented in this article. Data from the COPS network of stations are taken to identify the time and location of CI. In many cases this is not the same location as the first convective clouds, showers or even thunderstorms. It is shown that the interaction of the CI processes on multiple scales locally leads to either deep convection and severe storms or calm weather. The boundary conditions between the different outcomes are narrow.
During IOP 9c (20 July 2007), a mesoscale convective system (MCS) embedded in a surface low over eastern France propagated north-eastward and a gust front of the MCS reached the COPS area. During the passage of the gust front through the Rhine valley, convective activity was significantly reduced. The gust front reached the slope of the Black Forest, and the warm and humid air above the mountain range prior to the gust front was lifted up to 2000 m within a short time period. Within the air prior to the gust front aloft from the surface, CI started along a north–south oriented line above the crest. Due to insolation ahead of the gust front, a convergence line developed. The interaction of local-scale orographic winds, the regional-scale gust front, the mesoscale convergence line, and the synoptic-scale cold front led to a squall line. Finally, individual severe convective cells formed along the outer section of the synoptic-scale cold front. Copyright © 2011 Royal Meteorological Society
TL;DR: In this paper, a framework for the statistical analysis of large radar and lightning datasets is described and implemented in order to analyze two research questions in atmospheric electricity: storms dominated by positive cloud-to-ground (+CG) lightning and estimating the probability of lightning in convection.
Abstract: A framework for the statistical analysis of large radar and lightning datasets is described and implemented in order to analyze two research questions in atmospheric electricity: storms dominated by positive cloud-to-ground (+CG) lightning and estimating the probability of lightning in convection. The framework—a collection of computer programs running in series—is fully modular, allowing the analysis of a variety of datasets based on a study’s objectives, including radar observations, lightning data, observations of meteorological environments, and other data. The framework has been applied to over 2 months of observations of 28 463 cells. The results suggest that +CG-dominated cells contain midlevel positive charge (−10° to −30°C), in contrast to cells dominated by −CG lightning, which typically had positive charge at upper (near −40°C) and lower levels (0° to −10°C). The +CG cells also were larger and more intense, and were associated with environments that were more convectively favorable—in t...
TL;DR: The Airborne Detector for Energetic Lightning Emissions (ADELE), an array of gamma-ray detectors, was flown near the tops of Florida thunderstorms in August/September 2009.
Abstract: We report on the first search for Terrestrial Gamma-ray Flashes (TGFs) from altitudes where they are thought to be produced. The Airborne Detector for Energetic Lightning Emissions (ADELE), an array of gamma-ray detectors, was flown near the tops of Florida thunderstorms in August/September 2009. The plane passed within 10 km horizontal distance of 1213 lightning discharges and only once detected a TGF. If these discharges had produced TGFs of the same intensity as those seen from space, every one should have been seen by ADELE. Separate and significant nondetections are established for intracloud lightning, negative cloud-to-ground lightning, and narrow bipolar events. We conclude that TGFs are not a primary triggering mechanism for lightning. We estimate the TGF-to-flash ratio to be on the order of 10^(−2) to 10^(−3) and show that TGF intensities cannot follow the well-known power-law distribution seen in earthquakes and solar flares, due to our limits on the presence of faint events.
TL;DR: The spatial and temporal characteristics and distributions of thunderstorms in Taiwan during the warm season (May-October) from 2005 to 2008 and under weak synoptic-scale forcing are documented using radar reflectivity, lightning, radiosonde, and surface data as discussed by the authors.
Abstract: The spatial and temporal characteristics and distributions of thunderstorms in Taiwan during the warm season (May–October) from 2005 to 2008 and under weak synoptic-scale forcing are documented using radar reflectivity, lightning, radiosonde, and surface data. Average hourly rainfall amounts peaked in midafternoon (1500–1600 local solar time, LST). The maximum frequency of rain was located in a narrow strip, parallel to the orientation of the mountains, along the lower slopes of the mountains. Significant diurnal variations were found in surface wind, temperature, and dewpoint temperature between days with and without afternoon thunderstorms (TSA and non-TSA days). Before thunderstorms occurred, on TSA days, the surface temperature was warmer (about 0.5°–1.5°C) and the surface dewpoint temperature was moister (about 0.5°–2°C) than on non-TSA days. Sounding observations from northern Taiwan also showed warmer and higher moisture conditions on TSA days relative to non-TSA days. The largest average ...
TL;DR: In this article, the physical mechanisms, sensitivities and predictability of convective precipitation for a well-observed event from the Convective and Orographically induced Precipitation Study (COPS) were investigated.
Abstract: Convective-scale ensemble simulations with perturbed initial conditions are performed to investigate the physical mechanisms, sensitivities and predictability of convective precipitation for a well-observed event from the Convective and Orographically induced Precipitation Study (COPS). On this day an isolated thunderstorm developed over the Black Forest mountains in southwest Germany that was initiated by thermally driven low-level convergence. With the default ensemble configuration, none of the members simulated any deep convection. A soil moisture and atmospheric moisture deficiency was found to be responsible for a lack of boundary layer moisture in the analysis. Correction of this moisture bias yielded an ensemble in which some members produced a realistic convective storm. In contrast, other members only produced shallow convection. A robust feature of the members that simulated the storm was that an impinging upper-level disturbance to the west had progressed further east towards the COPS region. This led to increased westerly winds aloft, which when mixed down into the boundary layer acted to feed a deeper layer of moist valley air into the convergent mountain circulation. The simulations reveal a very strong sensitivity to uncertainties in the large-scale flow as well as the boundary layer structure and stability. Copyright © 2011 Royal Meteorological Society and British Crown Copyright, the Met Office
TL;DR: In this paper, the authors investigated the role of orography in the formation and evolution of the strong squall line in the early stages of a severe thunderstorm on the island of Mallorca in Spain.
TL;DR: In this article, a method is developed to quantify thunderstorm intensity according to cloud-to-ground lightning flashes (hereafter ground flashes) determined by a lightning-location sensor network.
Abstract: A method is developed to quantify thunderstorm intensity according to cloud-to-ground lightning flashes (hereafter ground flashes) determined by a lightning-location sensor network. The method is based on the ground flash density ND per thunderstorm day (ground flashes per square kilometer per thunderstorm day) calculated on 20 km × 20 km fixed squares. Because the square size roughly corresponds to the area covered by a typical thunderstorm, the flash density for one square defines a unit thunderstorm for the purposes of this study. This method is tested with ground flash data obtained from two nationwide lightning-location systems: the National Lightning Detection Network (NLDN) in the contiguous United States and the portion of the Nordic Lightning Information System (NORDLIS) in Finland. The distribution of daily ground flash density ND is computed for all of Finland and four 800 000 km2 regions in the United States (identified as western, central, eastern, and Florida). Although Finland and a...