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Sprite climatology in the Eastern Mediterranean Region

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  • Reichman University
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... Furthermore, the global distribution of superbolt activity exhibits a clear asymmetry in the two cases, with weaker events distributed in the ordinary tropical lightning hotspots while larger optical powers exceeding 350 GW showing similarity with previous results from Turman (1977), being highly concentrated in oceanic thunderstorms, and in particular at the mid-latitudes of Mediterranean Sea, the Sea of Japan and the North Pacific during the winter season. Winter thunderstorm dynamics in such areas enhances the production of strong +CG strokes associated with transient luminous events (TLE) activity (Takahashi et al., 2003;Hayakawa et al., 2004;Yair et al., 2015), suggesting the possibility that the brightest events identified by Peterson and Kirkland (2020) may occasionally precede TLEs development. Observations from the LSO (Lightning and Sprite Observations) experiment, on board of the International Space Station (ISS), additionally provided early examples of optical superbolt-TLE composite images (Blanc et al., 2007). ...
... An approximate geometry of the transmitter-receiver paths is shown in the map. activity is generally limited to the Mediterranean during winter (Yair et al., 2015;Arnone et al., 2020). The key factor for the formation of sprites is the magnitude of the vertical CMC of parent +CG stroke (Hu et al., 2002) and the subsequent rapid change in the above-cloud quasielectrostatic (QE) field. ...
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Lightning occurrence at higher latitudes in northwestern Europe is by far less frequent than mainland continental and the Mediterranean during most of the year. Yet, as recent studies suggest, this region harbors a large fraction of the most energetic lightning flashes on Earth, commonly referred to as superbolts. In this study, we examine the time/locations of intense cloud-to-ground (CG) strokes (>200 kA in absolute value), provided by Météorage for the 10.5-year period (from Jan 2010 to Jul 2020), to present a high-resolution map of their distribution, pointing out relevant discrepancies observed between -CG and + CG, respectively. We additionally investigate the potential of superbolts to result in short-lived optical phenomena above thunderstorms, collectively known as transient luminous events (TLEs). Observations in the region indicate that isolated superbolts with substantial charge moment change can produce sprites during low active marginal winter thunderstorms, in the absence of concurrent IC/CG activity several minutes before and after the event. An example is described when 3 sprites were captured in a similar context during the night of 7th/8th February 2016. We suggest that: i) convergence and aerosols advection from sea surface and busy shipping lanes may favour deep convection and cloud electrification on the English Channel with respect to surrounding areas. Inherent differences in cloud charge structure of sea based storms could lead to faster negative leader vertical velocity than those for storms over land, on average, and hence in larger peak currents, determining the winter peak of negative superbolts in the area; ii) areas occupied by the most populated superbolt clusters can be used to conduct future research in the region, aimed at better characterising microphysical properties of superbolts and their potential in generating TLEs.
... Sprites occur at an estimated global rate of 1 per minute (Chen et al., 2008) and are commonly found in mesoscale convective systems and in other types of summer storms in the United States (US), in Europe (Neubert et al., 2001;Lyons et al., 2008;B� or, 2013;Soula et al., 2015;B� or et al., 2018), in Argentina (Thomas et al., 2007), in China (Yang et al., 2017a), and in South Africa (Nnadih et al., 2018). Sprites have also been detected in winter thunderstorms in Japan and in the Mediterranean Sea (Takahashi et al., 2003;Yair et al., 2009bYair et al., , 2015, which normally exhibit smaller vertical scales and lower flash rates. ...
... The vertical dimension of winter thunderstorm cells is typically much less than that of summer thunderstorm cells due to the colder atmosphere and much weaker updrafts (see Figure 8 in Yair et al., 2015). Sprite producing winter cells reach altitudes of up to ~9 km in Japanese winter thunderstorms (Hayakawa et al., 2004) and between 6.5-km and 10-km altitude in Eastern Mediterranean winter thunderstorms Yair et al., 2009b), while summertime deep convective cells sometimes reach higher than 15-km altitude (Lyons et al., , 2009). ...
Article
We present a simple, efficient, and flexible three-dimensional electrostatic model for calculating the magnitude and direction of the electric field from the ground to the base of the ionosphere for a given thunderstorm charge configuration, with the aim of evaluating the possibility for sprite inception. The model is based on a method-of-images solution to Poisson's equation, assuming near vacuum conditions and with perfectly conducting upper and lower boundaries. A dipole electrical structure within each thundercloud is assumed, with a screening (shielding) charge above the cloud. The charge centers (main positive, main negative, and screening charge) are modeled with average structural characteristics of summer and winter thunderstorms. To simulate a positive or negative cloud-to-ground lightning discharge, the main positive or main negative charge center, respectively, is removed from the domain. The computed electric potential at each grid point is converted to the electric field and is compared against the value of the conventional breakdown field to obtain an indication of the possibility of electrical breakdown and hence the possibility of sprite inception. This simple model is particularly useful for performing a sensitivity study with respect to variation in thunderstorm cell charge configuration, with no assumption of symmetry in the horizontal or vertical directions. Implications of the presence of neighboring clouds at different relative stages of development on the possibility of sprite inception and on the displacement of sprites from the location of the parent thunderstorm are also examined, as well as clouds with inverted dipole charge configuration.
... Such a large number of observations allow for the first time detailed climatological studies to be performed over Europe and the Mediterranean Sea, therefore studying the geographical distribution and variability of mean TLE occurrence over a time span of several 1 3 years rather than looking at individual events. A Southern Mediterranean example was presented by Yair et al. (2015), and an introduction to the climatology presented here was published by Arnone et al. (2016). Despite being inhomogeneously distributed, the number of ground-based observed sprites largely exceeds that acquired globally from satellites over equivalent periods of time (Chen et al. 2008). ...
... This behaviour is very consistent among the 5 years of the sample. The activity in the Southern Mediterranean Sea is consistent with the onset of maritime thunderstorms in autumn and winter (see Yair et al. 2015 for further details). Comparison with Fig. 6 shows a remarkable consistency. ...
Article
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In 1999, the first sprites were observed above European thunderstorms using sensitive cameras. Since then, Eurosprite campaigns have been conducted to observe sprites and other transient luminous events (TLEs), expanding into a network covering large parts of Europe and coastal areas. In 2009 through 2013, the number of optical observations of TLEs reached a peak of 2000 per year. Because of this unprecedented number of European observations, it was possible to construct a climatology of 8394 TLEs observed above 1018 thunderstorm systems and study for the first time their distribution and seasonal cycle above Europe and parts of the Mediterranean Sea. The number of TLEs per thunderstorm was found to follow a power law, with less than 10 TLEs for 801 thunderstorms and up to 195 TLEs above the most prolific one. The majority of TLEs were classified as sprites, 641 elves, 280 halos, 70 upward lightning, 2 blue jets and 1 gigantic jet. The climatology shows intense TLE activity during summer over continental areas and in late autumn over coastal areas and sea. The two seasons peak, respectively, in August and November, separated by March and April with almost no TLEs, and a relative minimum around September. The observed TLE activity, i.e. mostly sprites, is shown to be largely consistent with lightning activity, with a 1/1000 of observed TLE-to-lightning ratio in regions with most observations. The overall behaviour is consistent among individual years, making the observed seasonal cycle a robust general feature of TLE activity above Europe.
... Sprites occur at an estimated global rate of 1 per minute (Chen et al., 2008) and are commonly found in mesoscale convective systems and in other types of summer storms in the United States (US), in Europe (Neubert et al., 2001;Lyons et al., 2008;B� or, 2013;Soula et al., 2015;B� or et al., 2018), in Argentina (Thomas et al., 2007), in China (Yang et al., 2017a), and in South Africa (Nnadih et al., 2018). Sprites have also been detected in winter thunderstorms in Japan and in the Mediterranean Sea (Takahashi et al., 2003;Yair et al., 2009bYair et al., , 2015, which normally exhibit smaller vertical scales and lower flash rates. ...
... The vertical dimension of winter thunderstorm cells is typically much less than that of summer thunderstorm cells due to the colder atmosphere and much weaker updrafts (see Figure 8 in Yair et al., 2015). Sprite producing winter cells reach altitudes of up to ~9 km in Japanese winter thunderstorms (Hayakawa et al., 2004) and between 6.5-km and 10-km altitude in Eastern Mediterranean winter thunderstorms Yair et al., 2009b), while summertime deep convective cells sometimes reach higher than 15-km altitude (Lyons et al., , 2009). ...
Article
We present results from a simple 2D model of the mesospheric electric field for several thunderstorm charge configurations. The model assumes a simple dipole structure with a screening charge above cloud-top. The charge centers are modeled as horizontal disks with a Gaussian charge density distribution. We solve the Poisson equation numerically, using a second order central finite difference scheme. A relaxation method is used over a grid of 90 x 300 points with a 1-km interval. We convert the computed electric potential at each grid point to the electric field and compare it to the breakdown field, thus mapping the regions where there exists a possibility for sprite initiation. This model allows the study of various thunderstorm cell configurations, with multiple cells and with different polarities. Four main charge configurations are examined: (1) a summer thunderstorm cell, (2) a winter cell, (3) simultaneous lightning from two summer cells, and (4) a summer cell with an inverse dipole. The results highlight the difference in the charge moment change (CMC) threshold needed for sprite generation in winter and summer cells. The effects of the presence of neighboring thunderclouds at different relative stages of development are presented, particularly with respect to the likelihood of sprite formation and the displacement of sprites from the parent flash. In addition, we show how the orientation of the electric field changes with altitude, potentially explaining the optical observations of sprite tendril curvature toward the cloud.
... However, Saaroni et al. (1998) indicated that trough is drawn northwards and activated by moisture, and finally flooded in the eastern Mediterranean Sea if it is accompanied by a high-level tropospheric trough. This is in line with the results of other studies (e.g., Krichak et al. 2000Krichak et al. , 2012De Vries et al. 2013;Haggag & Al-Badry 2013;Yair et al. 2015). Furthermore, discovered the Sudan low nature and RST using the mean sea level pressure (SLP) for the 1955-2015 winter period. ...
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The present study evaluated the dynamic changes in Sudan low systems over six decades (1957–2019), which were classified based on solar cycles. Rainfall days were extracted in January using data from 42 synoptic stations in the south and southwest regions of Iran. Then, the rainy days due to the Sudan low system were separated from the precipitation of the other atmospheric systems using the visual analysis of the maps. The synoptic analysis indicated that the sea level pressure has been decreasing at all sampling stations from the first to the sixth decade. Furthermore, decreasing elevation to −80 m (negative anomaly) in the 500 hPa level atmosphere from the first decade to the sixth decade indicated further atmospheric instability and more strengthening of the Sudan low compared to previous decades. The contribution of advection moisture to the area increased within the region at 700 hPa. This implies that the role of the transferred moisture from the intertropical convergence zone is increasing in the systems transferred from Sudan and in the study area. In general, the share of Sudan low precipitation is increasing in the south and southwest regions of Iran. This result is a positive effect of the climate change on the study area. HIGHLIGHTS This study describes the decadal changes in Sudanese low pressure affecting precipitation days in southwestern Iran.; Sea level pressures have been declining from the first decade to the sixth decade.; Sudan low pressure has intensified over the period under review.; The share of Sudan low pressure in the abundance of rainy days in the southern and southwestern regions of Iran is increasing.;
... Thus, cyclonic mid-latitude disturbances in mid-autumn, winter, and spring with high humidity in the low level lead to tropospheric instability and anomalous rainfall in the Arabian Peninsula (Barth and Steinkohl 2004;Evans et al. 2004;Chakraborty et al. 2006;Evans and Smith 2006;Nazemosadat and Ghaedamini 2010;Kumar et al. 2015). In the active events, Sudan low pressure is a serious threat to human society in northeast Africa and causes flood (El-Fandy 1947;Krichak et al. 2012;Kahana et al. 2002;De Vries et al. 2016;Yair et al. 2015). The Jeddah flood in November 2009 showed that Sudan low played a crucial role which was amplified by advancing to high latitude. ...
Article
The goal of the study is to analyze the trend and extent of Sudan low pressure with respect to climate change and its relation to the upper atmosphere levels and the influences of the variation on precipitation in October, November, December, January, February, and March during the period from 1951 to 2018. This period was divided into seven 10-year periods for a deeper analysis. It was found that the average geopotential height (hgt) in the two studied levels (1000 and 500 hPa) and all the periods, except for the first (1951 to 1960), had an increasing rate, which points to the weakening of the Sudan low pressure. The mean hgt at 1000 hPa increased with a slope of 0.9, 2.64, and 3.2 hgt for October, November, and December, and 3.6, 1.8, and 1.3 hgt for January, February, and March, respectively. The results showed that December and January had the highest rate of increase in pressure at 1000 hPa. The coefficients of variation (CV) had a significant trend of − 1.4, − 1.4, 0.08, − 0.19, − 0.36, and − 1.8% per decade for October, November, December, January, February, and March, respectively. The minimum and maximum hgt showed a noticeable increasing trend in the levels. The low-pressure extend showed a significant decreasing trend of 62,8347.3 and 62,440.8 km2 in December and January, respectively, which was significant at 0.01. There was a negative and significant correlation between hgt at 1000 hPa and precipitation of western and southwestern Iran in winter regardless of periods, whereas there was a significant negative correlation in Ahvaz taking the periods into account.
... We received the complete list of optical sprite observations from the ILAN science team. These data include time, azimuth, elevation, distance, physical description (for example, "carrot" or "column"), and number of elements (meaning the number of optically distinct structures) [18]. ...
Article
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Sprites are transient luminous events (TLEs) that occur at mesospheric altitudes between 50 and 90 km. They last up to several milliseconds, and are caused mostly by positive lightning discharges from the thunderstorm cells below. Infrasound from sprites was first observed in detail a decade ago by a team from the French Atomic Energy Commission (CEA), as part of a renewed international interest in infrasound measurements brought about by the Comprehensive Nuclear Test Ban Treaty (CTBT) (Farges et al., 2005). They used optical images of sprites obtained during the EuroSprite observation campaign in order to form the temporal and azimuthal basis necessary for searching for the infrasound signatures from these events, which appear as unique “chirp” or “inverted chirp” signatures depending on the sprite's distance from the infrasound array. In this paper we follow this methodology to see if the nascent Israeli infrasound arrays can detect these signals from sprites in the Eastern Mediterranean, for which there are nearly 8 years of winter-time optical observations. We calculated the expected arrival time of the infrasound from optically observed sprites, and then used a basic ray-tracing method in order to confirm that we were in fact able to observe several of these sprites, at various distances, exhibiting both “chirp” and “inverted chirp” signals. We then compared these observations with observations of lightning activity made by the World Wide Lightning Location Network (WWLLN).
... Red sprites, as one major type of lightning-induced transient luminous events (TLEs) above thunderstorms, are short-lived (typically < 20 ms) structured optical emissions that could be observed from both ground-based (Franz et al. 1990;Boccippio et al. 1995;Lyons 1996;Yair et al. 2015) and space-borne platforms (Yair et al. 2004;Chen et al. 2008;Jehl et al. 2013;Sato et al. 2015). The broad connection between sprites and energetic cloud-to-ground (CG) lightning strokes has been established by concurrent recording of distinct radio frequency electromagnetic pulses commonly registered upon the sprite observation (Reising et al. 1996;Cummer et al. 1998;Huang et al. 1999;Li et al. 2008;Lu et al. 2013). ...
Article
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We examined the broadband (<1 Hz to 30 kHz) lightning sferics associated with 395 sprites observed near North America by the Imager of Sprites and Upper Atmospheric Lightning (ISUAL) onboard the FORMOSAT-2 satellite in a 12-year period from 2004 to 2015. Our analysis indicates that the ISUAL dataset contains a significant fraction (69, or ~18%) of negative sprites, which were predominantly (>80%) observed over oceanic and coastal thunderstorms mostly in tropical areas. The mean and median of impulse charge moment change (iCMC) associated with positive (negative) sprites are +346 C km (-709 C km) and +280 C km (-649 C km), respectively. The morphology and parent lightning properties (e.g., typically with high peak currents >-80 kA and large iCMCs >-300 C km) of negative sprites observed by the ISUAL are generally consistent with that documented in ground-based observations, but the ISUAL dataset does imply that sprites are sometimes produced by negative strokes with sub-critical iCMCs (less than -300 C km). Consequently, the future survey of global occurrence of sprites is desired to be based on complementary ground and space-borne observations. © 2016 Terrestrial, Atmospheric and Oceanic Sciences (TAO). All rights reserved.
Article
The study of the global distribution of sprites is based on the new parameterization and WWLLN (World Wide Lightning Location Network) data for 2016. The information on the position, time, and power (peak current) for cloud-to-ground discharges are taken from the archive of the WWLLN. Parameterizations of the sprite initiation probability are proposed for positive and negative discharges. In the calculations, only nighttime events are considered and the probabilistic nature of the sprite initiation, depending on the iCMC, is taken into account. It is shown that on average 870 nighttime sprites per twenty-four hours globally can be initiated, 41.4% over land and 58.6% over ocean. On the basis of the proposed parametrization, the regional distribution of sprites is analyzed, as well as seasonal and monthly distribution over land and ocean. The annual dynamics of the number of sprites over land and ocean has been investigated, revealing the maximum number of events in August and the minimum in January and February.
Article
The spring Sudan low and its Red Sea Trough (RST) were detected objectively using sea level pressure (SLP) data obtained from an NCEP/NCAR reanalysis dataset spanning the period from 1955 to 2014. The climatology of the detected lows suggested that the Sudan low was active for approximately 69.5% of the spring and that approximately 56.2% of this time the Sudan low developed into the RST. Furthermore, three main genesis regions of the RST, which generated 95.25% of the RST, were identified over Sudan, South Sudan and the Red Sea, approximately 61.76% of which was over South Sudan. Additionally, three main outermost areas of the RST, which received 94.1% of the RST, were specified to the west, east and north of the Red Sea, approximately 54.88% of which was in the eastern region. Synoptically, the orientations of the detected RST around the Red Sea are strongly influenced by the Siberian and Azores high systems. The RST is directed along the western side of the Red Sea if the Siberian high extends westward and the Azores high shrinks westward, whereas the RST is oriented to the east if the Siberian high shrinks eastward and the Azores high extends eastward. The RST extends directly northward if the Siberian and Azores high systems withdraw eastward and westward, respectively. These results also demonstrate that the core position and strength of the upper maximum winds play an important role in the generation of RST. The selected case studies have confirmed the synoptic climate results and indicate that the Sudan low will not develop into RST when the northern region has been affected by a high‐pressure system and the core of the upper maximum wind is located over the northern Arabian Peninsula. This article is protected by copyright. All rights reserved.
Article
In this study, a new and objective method for detecting the Red Sea Trough (RST) was developed using mean sea level pressure (SLP) data from NCEP/NCAR reanalysis dataset from the winters of 1956 to 2015 to identify the Sudan Low and its trough. Approximately 96% of the winter RSTs were generated near two main sources, South Sudan and southeastern Sudan, and approximately 85% of these troughs were in four of the most outer areas surrounding the northern Red Sea. Moreover, from west to east of the Red Sea, the RST was affected by the relationships between the Siberian High and Azores High. The RST was oriented to the west when the strength of the Siberian High increased and to the east when the strength of the Azores High increased. Furthermore, the synoptic features of the upper level of the RST emphasize the impacts of subtropical anticyclones at 850 hPa on the orientation of the RST, the impacts of the northern cyclone trough and the maximum wind at a pressure level of 250 hPa. The average static stability between 1000 hPa and 500 hPa demonstrated that the RST followed the northern areas of low static stability. The results from previous studies were confirmed by a detailed case study of the RST that extended to its central outermost area. The results of a detailed case study of the short RST indicated that the trough becomes shorter with increasing static stability and that the Azores and Siberian high-pressure systems influence the northern region of the trough while the maximum upper wind shifts south of the climate position.
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The amount of airborne particles that will nucleate and form cloud droplets under specific atmospheric conditions, depends on their number concentration, size distribution and chemical composition. Aerosol is affected by primary particle emissions, gas-phase precursors, their transformation and interaction with atmospheric constituents, clouds and dynamics. A comprehensive assessment of these interactions requires an integrated approach; most studies however decouple aerosol processes from cloud and atmospheric dynamics and cannot account for all the feedbacks involved in aerosol-cloud-climate interactions. This study addresses aerosol-cloud-climate interactions with the Integrated Community Limited Area Modeling System (ICLAMS) that includes online parameterization of the physical and chemical processes between air quality and meteorology. ICLAMS is an extended version of the Regional Atmospheric Modeling System (RAMS) and it has been designed for coupled air quality – meteorology studies. Model sensitivity tests for a single-cloud study as well as for a case study over the Eastern Mediterranean illustrate the importance of aerosol properties in cloud formation and precipitation. Mineral dust particles are often coated with soluble material such as sea-salt, thus exhibiting increased CCN efficiency. Increasing the percentage of salt-coated dust particles by 15% in the model resulted in more vigorous convection and more intense updrafts. The clouds that were formed extended about 3 km higher and the initiation of precipitation was delayed by one hour. Including on-line parameterization of the aerosol effects improved the model bias for the twenty-four hour accumulated precipitation by 7%. However, the spatial distribution and the amounts of precipitation varied greatly between the different aerosol scenarios. These results indicate the large portion of uncertainty that remains unresolved and the need for more accurate description of aerosol feedbacks in atmospheric models and climate change predictions.
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Gridded climatologies of total lightning flash rates observed by the spaceborne Optical Transient Detector (OTD) and Lightning Imaging Sensor (LIS) instruments have been updated. OTD collected data from May 1995 to March 2000. LIS data (equatorward of about 38°) adds the years 1998-2010. Flash counts from each instrument are scaled by the best available estimates of detection efficiency. The long LIS record makes the merged climatology most robust in the tropics and subtropics, while the high latitude data is entirely from OTD. The gridded climatologies include annual mean flash rate on a 0.5° grid, mean diurnal cycle of flash rate on a 2.5° grid with 24 hour resolution, mean annual cycle of flash rate on a 0.5° or 2.5° grid with daily, monthly, or seasonal resolution, mean annual cycle of the diurnal cycle on a 2.5° grid with two hour resolution for each day, and time series of flash rate over the sixteen year record with roughly three-month smoothing. For some of these (e.g., annual cycle of the diurnal cycle), more smoothing is necessary for results to be robust.The mean global flash rate from the merged climatology is 46 flashes s- 1. This varies from around 35 flashes s- 1 in February (austral summer) to 60 flashes s- 1 in August (boreal summer). The peak annual flash rate at 0.5° scale is 160 fl km- 2 yr- 1 in eastern Congo. The peak monthly average flash rate at 2.5° scale is 18 fl km- 2 mo- 1 from early April to early May in the Brahmaputra Valley of far eastern India. Lightning decreases in this region during the monsoon season, but increases further north and west. An August peak in northern Pakistan also exceeds any monthly averages from Africa, despite central Africa having the greatest yearly average.
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Sprites are spectacular optical emissions in the mesosphere induced by transient lightning electric fields above thunderstorms. Although the streamer nature of sprites has been generally accepted, how these filamentary plasmas are initiated remains a subject of active research. Here we present observational and modelling results showing solid evidence of pre-existing plasma irregularities in association with streamer initiation in the D-region ionosphere. The video observations show that before streamer initiation, kilometre-scale spatial structures descend rapidly with the overall diffuse emissions of the sprite halo, but slow down and stop to form the stationary glow in the vicinity of the streamer onset, from where streamers suddenly emerge. The modelling results reproduce the sub-millisecond halo dynamics and demonstrate that the descending halo structures are optical manifestations of the pre-existing plasma irregularities, which might have been produced by thunderstorm or meteor effects on the D-region ionosphere.
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Cloud-to-ground lightning flashes usually consist of one or several strokes coming in very short temporal succession and close spatial proximity. The common method for converting stroke data into flashes is using the National Lightning Detection Network (NALDN) thresholds of maximum temporal separation of 0.5 s and maximum lateral distance of 10 km radius between successive strokes. In the present study, we tested a location-based algorithm with several spatial and temporal ranges, and analyzed stroke data obtained by the Israel Lightning Location System (ILLS) during one year (1 August 2009-31 July 2010). We computed the multiplicity, the percentage of single stroke flashes and the geographical distribution of single vs. multiple-stroke flashes for thunderstorms in the Eastern Mediterranean region. Results show that for the NALDN thresholds, the percentage of single stroke flashes in Israel was 37% and the average multiplicity was 1.7. We re-analyzed the data with a spatial range that equals twice the ILLS location error and shorter times. For the new thresholds of maximum distance of 2.5 km and maximum allowed temporal separation of 0.2 s we find that the mean multiplicity of negative CGs is lowered to 1.4 and find a percentage of 58% of single stroke flashes. A unique severe storm from 30 October 2009 is analyzed and compared to the annual average of 2009/10, showing that large deviations from the mean values can occur in specific events.
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During a thunderstorm on 23 July 2003, 15 sprites were captured by a LLTV camera mounted at the observatory on Pic du Midi in the French Pyrénées. Simultaneous observations of cloud-to-ground (CG) and intracloud (IC) lightning activity from two independent lightning detection systems and a broadband ELF/VLF receiver allow a detailed study of the relationship between electrical activity in a thunderstorm and the sprites generated in the mesosphere above. Results suggest that positive CG and IC lightning differ for the two types of sprites most frequently observed, the carrot- and column-shaped sprites. Column sprites occur after a short delay (<30 ms) from the causative +CG and are associated with little VHF activity, suggesting no direct IC action on the charge transfer process. On the other hand, carrot sprites are delayed up to about 200 ms relative to their causative +CG stroke and are accompanied by a burst of VHF activity starting 25-75 ms before the CG stroke. While column sprites associate with short-lasting (less than 30 ms) ELF/VLF sferics, carrot sprites associate with bursts of sferics initiating at the time of the causative +CG discharge and persisting for 50 to 250 ms, indicating extensive in-cloud activity. One carrot event was found to be preceded by vigorous IC activity and a strong, long-lived cluster of ELF/VLF sferics but lacking a +CG. The observations of ELF/VLF sferic clusters associated with lightning and sprites form the basis for a discussion of the reliability of lightning detection systems based on VHF interferometry.
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Carrot sprites, exhibiting both upward and downward propagating streamers, and columniform sprites, characterized by predominantly vertical downward streamers, represent two distinct morphological classes of lightning-driven transient luminous events in the upper atmosphere. It is found that positive cloud-to-ground lightning discharges (+CGs) associated with large charge moment changes (QhQ) tend to produce carrot sprites with the presence of a mesospheric region where the electric field exceeds the value 0.8Ek and persists for > ˜ 2 ms, whereas those associated with small QhQ are only able to produce columniform sprites. Columniform sprites may also appear in the periphery of a sprite halo produced by +CGs associated with large QhQ. For a sufficiently large QhQ, the time dynamics of the QhQ determines the specific shape of the carrot sprites. In the case when the sufficiently large QhQ is produced mainly by an impulsive return stroke, strong electric field is produced at high altitudes and manifests as a bright halo, and the corresponding conductivity enhancement lowers/enhances the probability of streamer initiation inside/below the sprite halo. A more impulsive return stroke leads to a more significant conductivity enhancement (i.e., a brighter halo). This conductivity enhancement also leads to fast decay and termination of the upper diffuse region of carrot sprites because it effectively screens out the electric field at high altitudes. On the contrary, if the sufficiently large QhQ is produced by a weak return stroke (i.e., a dim halo) accompanied by intense continuing current, the lightning-induced electric field at high altitudes persists at a level that is comparable to Ek, and therefore an extensive upper diffuse region can develop. Furthermore, we demonstrate that `negative sprites' (produced by -CGs) should be necessarily carrot sprites and most likely accompanied by a detectable halo, since the initiation of upward positive streamers is always easier than that of downward negative streamers, and -CGs are usually associated with impulsive return stroke with no continuing current. We also conjecture that in some cases, fast decaying single-headed upward positive streamers produced by -CGs may appear as bright spots/patches. We show that the threshold charge moment changes of positive and negative sprites are, respectively, ~320 and ~500 C km under typical nighttime conditions assumed in this study. These different initiation thresholds, along with the different applied electric field required for stable propagation of positive and negative streamers and the fact that +CGs much more frequently produce large charge moment changes, represent three major factors in the polarity asymmetry of +CGs and -CGs in producing sprite streamers. We further demonstrate that lower mesospheric ambient conductivity leads to smaller threshold charge moment change required for the production of carrot sprites. We suggest that geographical and temporal conductivity variations in the lower ionosphere documented in earlier studies, along with the seasonal and inter-annual variations of thunderstorm activity that lead to different lightning characteristics in the troposphere, account for the different morphological features of sprites observed in different observation campaigns.
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Electric field (E) soundings through convective regions of mesoscale convective systems (MCSs) are examined in this paper. Ten E soundings through updrafts in MCS convective regions and five soundings in MCS convective regions outside updrafts are used to show that a typical electrical structure exists in this region. These 15 E soundings plus one other previously published sounding, which is included in this analysis, comprise all known soundings in the convective region of MCSs. The basic charge structure identified in MCS updrafts consists of four charge regions, alternating in polarity, with the lowest region positive and the highest region negative. The basic charge structure outside updrafts in MCS convective regions has six charge regions, alternating in polarity, with a positive charge region lowest. Maximum E magnitudes of both polarities are larger and are located at lower heights in soundings outside updrafts compared to those within updrafts. Excepting the upper positive charge, inferred charge regions are shallower and have larger charge densities outside updrafts. The center of the main negative charge is lower and warmer outside updrafts (5.5 km, -6.2°C) than within updrafts (6.9 km, -15.7°C). These features inside and outside updrafts are incorporated in a new conceptual model of MCS convective region charge structure. Also, an expanded conceptual model is developed, using previously published data from other parts of MCSs. This more complete conceptual model shows the typical electrical charge, airflow, and reflectivity features in the stratiform region, the transition zone, and the convective region of midlatitude mesoscale convective systems.
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The results of the 2005-6 winter sprite campaign in Israel are reported. We conducted optical ground-based observations aiming to detect transient luminous events (TLEs) above winter thunderstorms in Israel and in the area over the Mediterranean Sea between Israel, Cyprus and Lebanon. We alternated between two observation sites: the Tel-Aviv University campus in central Tel-Aviv (32.5N, 34.5E) and the Wise astronomical observatory in the Negev desert, near Mitzpe-Ramon (30N, 34.5E). We used 2 WATEC cameras, mounted on a pan-and- tilt unit with GPS time-base and event-detection software (UFO-Capture). The system was remote-controlled via the Internet and targets were chosen in real-time based on lightning locations derived from a BOLTEK lightning detection system stationed in Tel-Aviv. Detailed weather forecasts and careful analysis of lightning probability allowed us to choose between the two observation sites. The optical campaign was accompanied by ELF and VLF electromagnetic measurements from the existing TAU array in southern Israel. During five separate winter storms (December 2005 through March 2006) we detected 31 events: 27 sprites (4 halo sprites) and 4 elves. Detection ranges varied from 250 to 450km. Sprites were found to occur almost exclusively over the sea, in the height range 44-105km. Most sprites were columnar, and the number of elements varied from 1 to 9 with lengths varying from 10 to 48km. The average duration of sprites was ~43ms. All TLEs were accompanied by distinct positive ELF transients, which were clearly identified by our ELF station in Mizpe-Ramon and by the ELF station near Sopron, Hungary (range ~2500km). Calculated charge moment values were 800-1870 C·km, with some events exceeding 2500 C·km. We employed different lightning location systems (Israel Electrical Company LPATS and TOGA, ZEUS global networks) to determine the ground location of the parent lightning and succeeded in geo-locating 7 events. Based on weather radar and satellite images, it was found that most of the thunderclouds that produced sprites were isolated Cumulonimbus cells embedded within a matrix of lower rain clouds, associated with the cold sector of Cyprus lows. The relationship between the meteorological parameters, storm size, vertical cloud development and lightning properties, as well as a comparison with the properties of thunderstorms producing winter sprites in Japan, will be presented.
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During the evening of 6 August 2008, a small mesoscale convective system (MCS) entered the area of radar and 2-D interferometric lightning detection system coverage in northeastern Spain and produced 17 sprites recorded by a camera at only 95–180 km distance. This study presents an analysis of the in-cloud component of the sprite-associated lightning flashes and those of other flashes. The analysis focuses on the horizontal development of sprite-producing lightning by discussing three examples, divided into the periods before the positive cloud-to-ground flash (+CG), between +CG and the end of the sprite, and the period after the sprite. Location and horizontal size of sprites appear to be well explained by the temporal and spatial development of the lightning path. The majority of sprite-producing discharges started directly at the rear side of developing and mature convective cores within the decaying MCS, either with the +CG or with preceding negative leaders. The +CG started a burst of VHF sources during which the sprite developed. Delayed carrot sprites developed after a secondary, smaller burst and were well collocated with the burst toward the rear of the MCS. The order of development of elements in a grouped sprite followed the direction of lightning propagation during the burst stage. The second part of the analysis concentrates on the metrics of sequences of VHF sources and shows that sprites are indeed produced by the largest, longest lasting discharges with particularly large line-perpendicular dimensions (37 km median compared with 11 km for +CG >25 kA).
Article
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During the winter of 2005–6, optical ground-based observations were performed to detect transient luminous events (TLEs) above winter thunderstorms in the vicinity of Israel and the eastern coastline of the Mediterranean Sea. Two sites were used: the Tel Aviv University (TAU) campus in Tel-Aviv (32.5N, 34.5E) and the Wise astronomical observatory in the Negev desert (30.6N, 34.76E). We also conducted ELF and VLF electromagnetic measurements from the TAU array in southern Israel. In 4 different winter storms we detected 30 events: 26 sprites and 4 elves. The detection ranges varied from 250 to 450 km. Sprites were found to be produced exclusively by +CGs that can be traced to active cells with a vertical dimension of 5–7 km and cloud top temperature ∼−40°C, embedded in a much larger matrix of stratiform cloudiness. This configuration closely resembles the conditions for winter sprites in the Hokuriku region of Japan.
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The size distribution and chemical composition of aerosol particles during a dust storm in the eastern Mediterranean are analyzed. The data were obtained from airborne measurements during the Mediterranean Israeli Dust Experiment (MEIDEX). The dust storm passed over the Mediterranean Sea and extended up to an altitude of about 2.5 km. The uniqueness of this dust storm is that approximately 35% of the coarse particles up to about 1 km in height were internally mixtures of mineral dust and sea salt. Just north of the dust storm, large convective clouds developed, and heavy rain was recorded by the radar on the Tropical Rainfall Measuring Mission satellite. The chemical and physical properties of the particles are used as initial conditions for conducting a sensitivity simulation study with the two-dimensional detailed spectral bin microphysical model of Tel Aviv University. The simulations show that ignoring the ice-nucleating ability of the mineral dust, but allowing the soluble component of the mixed aerosols to act as efficient giant cloud condensation nuclei (CCN), enhances the development of the warm rain process in continental clouds. In our simulations the rain amounts increased by as much as 37% compared to the case without giant CCN. Introducing similar coarse-mode particles into more maritime-type clouds does not have significant effect on the cloud or on the amount of rainfall. On the other hand, allowing the mineral dust particles to also act as efficient ice nuclei (IN) reduces the amount of rain on the ground compared to the case when they are inactive. The simulations also reveal that under the same profiles of meteorological parameters, maritime clouds develop precipitation earlier and reach lower altitudes than continental clouds. When the dust particles are active as both giant CCN and effective IN, the continental clouds become wider, while the effects on the more maritime clouds is very small.
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During the night of 22-23 February 2006, more than 400 middle-atmospheric optical discharges were observed above one large thunderstorm system over northeastern Argentina. These transient luminous events (TLEs) were imaged during the Southern Brazil Sprite Campaign, the first campaign to focus on TLEs over southern Brazil, northeastern Argentina, and Uruguay. All of the TLEs were imaged from the Brazilian Southern Space Observatory (SSO) near Santa Maria, which is nearly in the center of the southernmost Brazilian state of Rio Grande do Sul. Although the fields of view of the imaging cameras were too narrow to view the entire storm, the more than 400 confirmed TLEs imaged indicate that this storm ranks as the third most active TLE producer ever reported. Hence, storms in this region of South America might be some of the leading TLE generators on Earth.
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The experiment LSO (Lightning and Sprite Observations) is dedicated to the optical study, from the International Space Station, of sprites occurring in the upper atmosphere above thunderstorms. The objectives were to study these phenomena and to validate a new measurement concept for future measurements of sprites from space at the nadir. The first measurements were performed in the frame of the flight of the French Astronaut Claudie Haigneré (mission Andromède) in October 2001. Observations were performed by two microcameras, one in the visible and near-infrared and the other equipped with a moderately wide band filter at 761 nm. This filter includes the most intense N2 1P emission of the sprites and partly the oxygen absorption A band of the atmosphere. The light emissions from sprites occurring in the middle and upper atmosphere are then differentiated from the emissions from lightning, occurring more deeply in the atmosphere and then more absorbed. This paper presents the first observations of sprites from space at the nadir and statistics about the respective intensities of lightning and sprites emissions as observed with this experiment.
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We present the results of a continuing survey of lightning characteristics in Tel-Aviv, Israel, for the period 1989-1996, based on daily registrations of a CGR3 lightning flash counter [Mackerras, 1985]. The lightning season in Israel lasts from October to April, and the long-term average of the annual flash density in the Tel-Aviv area was found to be 4.7+/-2.3km-2y-1. The mean intracloud/cloud-to-ground flash ratio was found to be 2.5+/-1.3, with maxima in the autumn months. This may be attributed to the higher altitudes of the -10°C and -25°C isotherms (which signify the locations of charge centers) and to the weaker wind shears that occur in these months. The average fraction of positive ground flashes (PGF) in Tel-Aviv thunderstorms was F=0.16+/-0.08. Storms that exhibited larger than average PGF fraction were found to be subjected to a strong shear of the horizontal wind. The observed empirical relation between the PGF fraction and the intensity of the wind shear W (in ms-1km-1) was logF=0.3050W+0.073.
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Transient luminous events (sprites, blue jets, elves) above large mesoscale convective systems (MCSs) over the U.S. High Plains have been routinely monitored from the Yucca Ridge Field Station near Fort Collins, Colorado using ground-based low-light video systems. We analyzed 36 sprites above the Nebraska MCS of August 6, 1994. The results lend further support to the hypothesis that sprites are almost uniquely associated with positive cloud-to-ground (+CG) lightning flashes. Sprite-associated +CGs also averaged substantially larger peak currents than the remaining +CG population (81 kA versus 30 kA in this storm system). There is some evidence that sprite-associated +CGs also have higher stroke multiplicity. This study yields no evidence of sprites associated with negative CG events. In the central United States an additional requirement appears to be that the parent MCS has a contiguous radar reflectivity area exceeding 20-25,000 km 2. The majority of the sprites occur above the large stratiform precipitation region and not the high-reflectivity convective core of the MCS. Triangulation of a limited number of paired images (from September 7, 1994) suggests that the sprite is generally centered within 50 km of the parent +CG. Assuming the +CG provides the range, single-image photogrammetric analyses provide estimates of the maximum vertical extent of the sprites. For this storm the sprite tops averaged 77 km with a maximum of 88 km. The bases averaged 50 km but with a few sprite tendrils extending as low as 31 km.
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The spatio-temporal distribution of lightning flashes over Israel and the neighboring area and its relation to the regional synoptic systems has been studied, based on data obtained from the Israel Lightning Location System (ILLS) operated by the Israel Electric Corporation (IEC). The system detects cloud-to-ground lightning discharges in a range of ~500 km around central Israel (32.5° N, 35° E). The study period was defined for annual activity from August through July, for 5 seasons in the period 2004–2010. The spatial distribution of lightning flash density indicates the highest concentration over the Mediterranean Sea, attributed to the contribution of moisture as well as sensible and latent heat fluxes from the sea surface. Other centers of high density appear along the coastal plain, orographic barriers, especially in northern Israel, and downwind from the metropolitan area of Tel Aviv, Israel. The intra-annual distribution shows an absence of lightning during the summer months (JJA) due to the persistent subsidence over the region. The vast majority of lightning activity occurs during 7 months, October to April. Although over 65 % of the rainfall in Israel is obtained during the winter months (DJF), only 35 % of lightning flashes occur in these months. October is the richest month, with 40 % of total annual flashes. This is attributed both to tropical intrusions, i.e., Red Sea Troughs (RST), which are characterized by intense static instability and convection, and to Cyprus Lows (CLs) arriving from the west. Based on daily study of the spatial distribution of lightning, three patterns have been defined; "land", "maritime" and "hybrid". CLs cause high flash density over the Mediterranean Sea, whereas some of the RST days are typified by flashes over land. The pattern defined "hybrid" is a combination of the other 2 patterns. On CL days, only the maritime pattern was noted, whereas in RST days all 3 patterns were found, including the maritime pattern. It is suggested that atmospheric processes associated with RST produce the land pattern. Hence, the occurrence of a maritime pattern in days identified as RST reflects an "apparent RST". The hybrid pattern was associated with an RST located east of Israel. This synoptic type produced the typical flash maximum over the land, but the upper-level trough together with the onshore winds it induced over the eastern coast of the Mediterranean resulted in lightning activity over the sea as well, similar to that of CLs. It is suggested that the spatial distribution patterns of lightning may better identify the synoptic system responsible, a CL, an "active RST" or an "apparent RST". The electrical activity thus serves as a "fingerprint" for the synoptic situation responsible for its generation.
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Results are presented from the first European campaign for observation of sprites, conducted during the summer of 2000 from the French astronomical observatory, Observatoire Midi-Pyrénées. The primary objective was to establish if sprites are generated over Europe and to identify the characteristics of the associated thunderstorms. During the one-month campaign local weather conditions allowed observations approximately half of the nights. Sprites were observed two nights over the Alps and one night over southeastern France in connection with cold fronts moving in from the Atlantic. In all, 40 sprites were recorded, including dancing sprites, multiple carrot sprites and c-sprites. The weather conditions were almost identical during the 3 nights, with the active area forming on the front-side of the cold fronts. The storms are not of the same magnitude as active systems often observed over the North American plains. Even so, sprites seem to be a common occurrence also over Europe.
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The transient ELF(∼50–5000 Hz) magnetic field radiated by lightning discharges across North America was continuously measured at Duke University during the summer of 2000. In total, 881 sprite-associated lightning discharges over 17 days were analyzed. We report in detail on 76 sprites for which we could reliably determine the lightning charge moment change from the ELF data at the time of sprite onset. The charge moment change for the initiation of a sprite is found to be as low as 120 C km. By folding together the charge moment distributions of sprite-producing lightning and all positive lightning, we find that the probability of sprite generation for lightning with >1000 C km charge moment change in 90%, while the sprite probability for lightning with
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Sprites and halos in the mesosphere are produced electrostatically by lightning ground flashes whose polarity is positive, by a margin of at least 1000 to 1 in collected observations. The initiation of these events is controlled by the vertical charge moment change of the flash. Schumann resonance ELF methods have been used to measure the charge moments of millions of flashes worldwide. The bipolar distributions of these events show stronger positive than negative tails, consistent with the predominance of ``positive'' sprites, but the negative tail of supercritical events is still of the order of 10% of the total supercritical population, more than 1 order of magnitude larger than the observed fraction of ``negative'' sprites. This juxtaposition constitutes a paradox. The suggested resolution of the paradox is that the more impulsive population of supercritical negative flashes is producing dim halos that are not readily detected in conventional video imagery. Additional sensitive, high-resolution, and high-speed imager (
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A phenomenon characterized by a tongue of low pressure extending northward from the southern Red Sea [Red Sea Trough (RST)] toward the eastern Mediterranean Sea (EM) is analyzed. In general, the RST is associated with hot and dry weather, resulting from east-southeasterly flows in the lower troposphere. In some cases, the RST is found to be accompanied by an upper-tropospheric trough extending from the north over the EM. Such conditions are associated with unstable stratification, favoring the development of mesoscale convective systems. This kind of RST has been defined as an ''active'' RST (ARST). The ARST phenomenon represents a serious threat to human society in the northeastern Africa–southeastern Mediterranean region, being in some cases associated with devastating floods. In this study, a conceptual model of the ARST phe-nomenon is discussed, and then an algorithm for the identification of ARST events is presented. The iden-tification algorithm has been applied to a multiyear NCEP–NCAR reanalysis data archive for both RST and ARST events. From the results of a composite analysis of several different atmospheric flow parameters associated with ARST events, the key features associated with ARST events are identified. The results from the analysis of the composite patterns support the suggestion that high amounts of moisture transported from tropical Africa in the form of an atmospheric river to the Red Sea–EM play a key role in determining the intensity of the ARST events.
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The Atmosphere-Space Interactions Monitor (ASIM) is an instrument suite to be mounted on one of the external platforms on the International Space Station (ISS). It will study the coupling of thunderstorms processes to the upper atmosphere, ionosphere and radiation belts, and energetic space particle precipitation effects in the mesosphere and thermosphere. The scientific objectives include (1) investigations into sprites, jets, elves and relativistic electron beams injected into the magnetosphere above thunderstorms, (2) studies of gravity waves in the thermosphere above severe thunderstorms, (3) auroral energetics, and (4) ozone and NOx concentrations in the upper atmosphere. The instruments are 6 TV frame-rate, narrow-band optical cameras, 6 100kHz-photometers, and one X-ray sensor. The mission includes instrument teams from Denmark, Spain, Norway and the US, and science teams from around the world. The mission is developed within the European Space Agency (ESA). ASIM is entering Phase B with expected launch in 2011.
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This paper presents a study of the characteristics of lightning activity during the Cyprus low winter storms over the eastern coast of the Mediterranean. The focus is on changes in the nature of thunderstorms crossing the coastline from the sea into the northern and central parts of Israel, as manifested in their electrical activity. It is based on the Lightning Position and Tracking System (LPATS) measurements of lightning ground strikes during four winter seasons between 1995 and 1999. The spatial distribution shows a maximum of lightning ground strikes over Mount Carmel, possibly due to its topographical forcing. The annual variation shows a major maximum in January with two minor peaks, one in November and another in March, which can be explained by changes in the static instability of the atmosphere throughout the rainy period. The average fraction of positive ground flashes was found to be 6% and their average peak current 41 kA. The average peak current of negative ground flashes was 27 kA. Larger frequencies of ground flashes were detected over the sea than over land during the study period. This is probably due to the large heat and humidity fluxes from the sea surface, which destabilize the colder air above and drive cloud convection. The annual distribution shows that during midwinter (December–January– February) there is higher flash density over the sea, while during autumn and spring the flash density is similar above the two regions. The diurnal variation shows that the maximum in maritime lightning activity was at 0500 LST and over land at 1300 LST. The mean peak current of positive ground flashes was higher over land and of negative ground flashes, over the sea.
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This paper presents a study of the characteristics of lightning activity during the Cyprus low winter storms over the eastern coast of the Mediterranean. The focus is on changes in the nature of thunderstorms crossing the coastline from the sea into the northern and central parts of Israel, as manifested in their electrical activity. It is based on the Lightning Position and Tracking System (LPATS) measurements of lightning ground strikes during four winter seasons between 1995 and 1999. The spatial distribution shows a maximum of lightning ground strikes over Mount Carmel, possibly due to its topographical forcing. The annual variation shows a major maximum in January with two minor peaks, one in November and another in March, which can be explained by changes in the static instability of the atmosphere throughout the rainy period. The average fraction of positive ground flashes was found to be 6% and their average peak current 41 kA. The average peak current of negative ground flashes was 27 kA. Larger frequencies of ground flashes were detected over the sea than over land during the study period. This is probably due to the large heat and humidity fluxes from the sea surface, which destabilize the colder air above and drive cloud convection. The annual distribution shows that during midwinter (December–January– February) there is higher flash density over the sea, while during autumn and spring the flash density is similar above the two regions. The diurnal variation shows that the maximum in maritime lightning activity was at 0500 LST and over land at 1300 LST. The mean peak current of positive ground flashes was higher over land and of negative ground flashes, over the sea.
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1] We present the results of space-based observations of sprites obtained during the Mediterranean Israeli Dust Experiment (MEIDEX) sprite campaign conducted on board the space shuttle Columbia during its STS-107 mission in January 2003. A total of $6 hours of useful data were saved from 21 different orbits, of which 1/5 contained lightning. We imaged sprites from an altitude of 280 km using a calibrated multispectral camera above thunderstorms in various geographical locations, mainly in central Africa, northern Australia, and South America, and also over the Pacific and Indian Oceans. In this paper we report on sprites observed from ranges 1600–2000 km from the shuttle, at altitudes of 40–90 km above the ground. Their brightness was in the range of 0.3– 1.7 mega-Rayleighs (MR) in the 665 nm filter and 1.44–1.7 MR in the 860 nm filter. On the basis of the frequency of observed events and the number of tropical thunderstorms, we estimate the sprite rate in the tropics to be of the order of several per minute.
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1] We report the global transient luminous event (TLE) distributions and rates based on the Imager of Sprites and Upper Atmospheric Lightning (ISUAL) experiment onboard the FORMOSAT-2 satellite. ISUAL observations cover 45°S to 25°N latitude during the northern summer and 25°S to 45°N latitude during the northern winter. From July 2004 to June 2007, ISUAL recorded 5,434 elves, 633 sprites, 657 halos, and 13 gigantic jets. Surprisingly, elve is the dominant type of TLEs, while sprites/halos are a distant second. Elve occurrence rate jumps as the sea surface temperature exceeds 26 degrees Celsius, manifesting an ocean-atmosphere-ionosphere coupling. In the ISUAL survey, elves concentrate over the Caribbean Sea, South China Sea, east Indian Ocean, central Pacific Ocean, west Atlantic Ocean, and southwest Pacific Ocean; while sprites congregate over central Africa, Japan Sea, and west Atlantic Ocean. The ISUAL experiment observed global rates of 3.23, 0.50, 0.39, and 0.01 events per minute for elves, sprites, halos, and gigantic jets, respectively. Taking the instrumental detection sensitivity and the restricted survey area into account, the corrected global occurrence rates for sprites and elves likely are a factor of two and an order of magnitude higher, respectively. ISUAL observations also indicate that the relative frequency of high peak current lightning (>80 kA) is 10 times higher over the oceans than over the land. On the basis of the corrected ISUAL elve global occurrence rate, the total electron content at the lower ionosphere above elve hot zones was computed to be elevated by more than 5%.
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1] We report measurements of impulsive (2 ms) lightning charge moment changes in more than 1000 cloud-to-ground (CG) return strokes detected by the National Lightning Detection Network in three United States High Plains storms during the Severe Thunderstorm Electrification and Precipitation Study (STEPS) field program of 2000. The positive CG strokes (+CGs) in a mesoscale convective system exhibit an unusual charge moment distribution with a small median and long tail. Analysis suggests the presence of two different classes of +CGs in this MCS, one with small charge moment changes (50 C km) and the other containing larger charge moment changes (50 – 1400 C km). The distributions of negative cloud-to-ground stroke charge moment changes are roughly log-normal in shape with means varying from 17.7 to 36.8 C km. When combined with past measurements these means vary by a factor of 4 between storms, and there is probably not a single distribution that represents well all storms.
Article
[1] We have succeeded in observing sprites for winter lightning in the Hokuriku area (Japan Sea side) of Japan in the winter of 2001/2002. The optical results on 3 days are compared with the corresponding characteristics of parent (causative) lightning with particular attention to the significant differences between Hokuriku winter lightning and the more widely studied continental lightning. Despite significant differences with Hokuriku winter lightning, we have found nearly the same sprite properties as already observed in the U.S. continent with a significant difference (simpler shape for Hokuriku winter sprite). Then, we have also discussed the criteria for sprite occurrence. Specifically, two similar criteria are found: (1) cloud-to-ground discharges of positive polarity and (2) the presence of a certain threshold in vertical charge moment (200–300 C km) (roughly consistent with that for the U.S. continent). Mesoscale convective systems are not necessary to store the charge necessary for sprites, but the parent Hokuriku winter clouds are substantially smaller than the minimum scale for sprite occurrence in the continental lightning; however, it is larger in area than ordinary summer thunderclouds. However, there may exit another condition such as clustering or self-organizing effect of thunderclouds for sprite production.
Article
During the night of 01-02 September, 2009, seventeen distinct sprite events including 3 halos were observed above a storm in north-western Mediterranean Sea, with a video camera at Pic du Midi (42.93N; 0.14E; 2877 m). The sprites occurred at distances between 280 and 390 km which are estimated based on their parent CG location. The MCS-type storm was characterized by a trailing-stratiform structure and a very circular shape with a size of about 70,000 km2 (cloud top temperature lower than - 35 °C) when the TLEs were observed. The cloud to ground (CG) flash rate was large (45 min- 1) one hour before the TLE observation and very low (< 5 min- 1) during it. Out of the 17 sprite events, 15 parent + CG (P + CG) strokes have been identified and their average peak current is 87 kA (67 kA for the 14 events without halo), while the associated charge moment changes (CMC) that could be determined, range from 424 to 2088 ± 20% C km. Several 2-second videos contain multiple sprite events: one with four events, one with three events and three with two events. Column and carrot type sprites are identified, either together or separately. All P + CG strokes are clearly located within the stratiform region of the storm and the second P + CG stroke of a multiple event is back within the stratiform region. Groups of large and bright carrots reach ~ 70 km height and ~ 80 km horizontal extent. These groups are associated with a second pulse of electric field radiation in the ELF range which occurs ~ 5 ms after the P + CG stroke and exhibits the same polarity, which is evidence for current in the sprite body. VLF perturbations associated with the sprite events were recorded with a station in Algiers.
Article
[1] The temporal and spatial development of sprite-producing lightning flashes is examined with coordinated observations over an asymmetric mesoscale convective system (MCS) on 29 June 2011 near the Oklahoma Lightning Mapping Array (LMA). Sprites produced by a total of 26 lightning flashes were observed simultaneously on video from Bennett, Colorado and Hawley, Texas, enabling a triangulation of sprites in comparison with temporal development of parent lightning (in particular, negatively charged stepped leaders) in three-dimensional space. In general, prompt sprites produced within 20 ms after the causative stroke are less horizontally displaced (typically 30 km). However, both prompt and delayed sprites are usually centered within 30 km of the geometric center of relevant LMA sources (with affinity to negative stepped leaders) during the prior 100 ms interval. Multiple sprites appearing as dancing/jumping events associated with a single lightning flash could be produced either by distinct strokes of the flash, by a single stroke through a series of current surges superposed on an intense continuing current, or by both. Our observations imply that sprites elongated in one direction are sometimes linked to in-cloud leader structure with the same elongation, and sprites that were more symmetric were produced above the progression of multiple negative leaders. This suggests that the large-scale structure of sprites could be affected by the in-cloud geometry of positive charge removal. Based on an expanded dataset of 39 sprite-parent flashes by including more sprites recorded by one single camera over the same MCS, the altitude (above mean sea level, MSL) of positively charged cloud region tapped by sprite-producing strokes declined gradually from ~10 km MSL (−35°C) to around 6 km MSL (−10°C) as the MCS evolved through the mature stage. On average, the positive charge removal by causative strokes of sprites observed on 29 June is centered at 3.6 km above the freezing level or at 7.9 km above ground level.
Article
[1] Theoretical model calculations recently predicted the existence of mesospheric irregularities which assist the initiation of sprites. Here we report the experimental detection of a ∼3–19 km3 large mesospheric irregularity at ∼80–85 km height which is illuminated by the electromagnetic field of an intense positive cloud-to-ground lightning discharge. While the lightning discharge causes a prompt group of four sprites above the lightning discharge, the mesospheric irregularity is found at a horizontal distance at least ∼15–20 km away from the sprite group and it rebrightens ∼40–60 ms after the sprite group occurrence. This rebrightening is driven by a local quasi-static electric field enhancement with a charge moment ∼4–20 Ckm which causes the irregularity to develop a downward descending luminous column from ∼75–85 km height. The quasi-static electric field enhancement is caused by the reorganization of residual charge inside the thundercloud during a high-level activity of intracloud discharges with ∼10–20 pulses per ms. Such mesospheric irregularities might have an effect on the wave propagation of 100 kHz radio waves which are used for atomic time transfer and marine navigation.
Article
Sprites are luminous optical emissions accompanying electric discharges in the mesosphere. 489 sprite events have been observed with a TV frame rate video system in Central Europe from Sopron (47.68°N, 16.58°E, ˜230 m MSL), Hungary between 2007 and 2009. Characteristic sprite forms, i.e., column, wishbone, tree, angel, and carrot have been identified in the set of records. Characteristic morphological properties corresponding to each type are given; earlier definitions and observations as well as the related theoretical considerations are reviewed. Based on the knowledge and experience from high-speed imaging in sprite observations, probable time sequences of streamer propagation directions were associated with the characteristic sprite types. It is suggested that different streamer propagation sequences corresponding to different dynamic processes may result in similar sprite forms. Several occasionally detectable sprite features are noted and described: tendrils, glows, puffs, beads, and spots. Spots are distinguished from the similar beads by their characteristic brightness, size, and location relative to the bright body of the sprite. The events observed in Central Europe have been classified by the number of individual sprites and by the variety of types appearing in them. More than 90% of the recorded sprites were found to occur in clusters rather than alone, and more than half of the sprite clusters contained more than one sprite types. Jellyfish and dancing sprite events are described as being special subsets of sprite clusters. Statistical analysis of the occurrences of morphological types, various sprite features, and event durations indicated that jellyfish sprites and clusters of column sprites with glows and tendrils do not tend to have long optical lifetimes. Sprite events with more morphological types, on the other hand, more likely have extended durations. The maximum of the encountered event duration was lower for events with many sprite elements. Observed rates of glows and puffs may refer to the occupied height range of sprites. The importance of understanding the driving factors behind the development of various sprite types and sprite features is emphasized and some topics are suggested for further investigation.
Article
Very recently NASA astronauts took a new set of pictures from the International Space Station during night time in the frame of the NASA Crew Earth Observations program, giving a new opportunity to observe in color sprites and their parent lightning flashes. In about 20 hours of observations, non-directly dedicated to thunderstorm studies, fifteen sprites were observed from August 2011 to April 2012. Chromatic observations allow analyzing thoroughly the main components of the sprite radiation. The red and green emissions, observed in all the sprite images, are due to the radiation of the first positive band system of molecular nitrogen N2. The blue emission, present in only 2 out of fifteen sprites, is produced by the radiation of bands of the second positive band system of N2 and bands of the first negative band system of N2+ ions. It indicates the possible presence of ionization in these two sprites. The sprite brightness has been evaluated equivalent to the Jupiter one.
Article
Measurements indicate that surprisingly small charge moment changes of ˜200 C km in positive cloud-to-ground lightning discharges (+CGs) can initiate middle atmospheric gas discharges termed sprites. In the present work a plasma fluid model is used to demonstrate that for spherically symmetric initial electron density inhomogeneities, the initiation of sprites by such small charge moment changes is only possible when the ionospheric D-region electron density profile is characterized by a reference altitude h‧ greater than 90 km. Vertically elongated inhomogeneities are found to be more favorable for sprite initiation, which is consistent with recently published studies. It is calculated that for the same ionospheric conditions (i.e., inhomogeneities and h‧ values) that lead to initiation of sprites by +CGs associated with ˜200 C km charge moment changes, the minimum charge moment change required for initiation of sprites by -CGs is 300 C km.
Conference Paper
In the year 2000, the first 40 sprites were observed over European thunderstorms using low-light cameras. Since then, Eurosprite campaigns have been conducted to observe sprites and other transient luminous events (TLEs), expanding into a network covering large parts of Europe and coastal areas. Over 2009 to 2011, the number of optical observations of TLEs exceeded 1000 per year. We present a climatology of over 3500 TLE observations and study for the first time their distribution and seasonal cycle above Europe.
Article
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Article
A sprite campaign was conducted in the Hokuriku area of Japan during a winter of 2004/2005. On the basis of a combined analysis of the data from various instruments (CCD cameras, radar, VHF/LF∼MF lightning mapping system, field mill network, and ELF detector), we studied meteorological and electrical structures for winter thunderstorms and sprite-producing positive discharge. Typical winter sprite parent thunderstorms had a meso-scale cloud area with embedded small convective cells. Some small winter thunderstorms accompanied by the most frequent sprite events were found to cause 2∼3 sprite events during a short interval of about 3∼5 min. When the sprites were observed, the extent of the convective cells at 20 dBZ counter was atmost∼20 × 20 km. The VHF sources associated with sprites were located near south of the convective cell and were mapped within very small areas of at most∼10 × 10 km. This fact shows that some small winter thunderstorms can generate large positive charge associated with sprites. We will present the analysis of such a small thunderstorms with sprites and positive lightning discharges.
Article
VHF, LF, and ELF lightning events, thunderstorms, and surface electric fields related to sprites were observed simultaneously during the winter of 2004/2005 in Hokuriku, Japan. The analysis of these observations enables us to investigate the relationship among sprites, lightning characteristics, and thunderstorm structure just before sprite genesis. Typical winter sprite parent thunderstorms had a mesoscale cloud area with small, embedded convective cells. Positive charges responsible for sprites tend to reside in the upper part of the thunderstorms; only a few positive charges were assumed to be located in the lower part. The total amount of positive charges removed by a sprite-producing flash from the upper and lower parts of the thunderstorms were estimated to be approximately 100 C and as large as 300∼400 C, respectively. Active thunderstorms with lightning accompanied by transient currents tended to generate simple sprites; more complex sprites were excited by lightning with continuing currents, which were generated by a few active thunderstorms and thunderstorms with precipitating stratiform clouds. VHF sources related to sprites can be found in the range of 5 to 72 km. The range of displacement between a sprite element and the corresponding positive cloud-to-ground lightning discharge or the first VHF source was 6∼30 km, and the bottom of the sprite bodies was located between 66 and 74 km. On the basis of these results, we deduced that the complexity of sprite morphology might be attributed to the differences in lightning characteristics.
Article
This study draws together the available observations in the Schumann resonance frequency range to examine the general issue of sensitivity of ionospheric height variations to changes in ionizing radiation from the Sun on different timescales. Ionospheric height can be formally defined, and two characteristic heights are recognized in the Schumann resonance frequency range. In general, order of magnitude changes in radiation are needed to cause relative changes in ionospheric height as large as 10%, as is the case on both the diurnal and 11-year timescales. Changes in EUV radiation are probably insufficiently strong to account for either the 27-day or the 11-year variation in ionospheric height. More ionization-effective X radiation is needed, but much smaller height changes are expected on the solar rotation timescale because the variations in X radiation on this timescale are only tens of percent and not orders of magnitude. The annual variation in radiation from the Sun is only 7%, with an expected height variation less than 100 m, and this remains to be verified by observations. The general insensitivity of the Schumann resonance cavity to changes in ionizing radiation lends stability to the medium that is valuable toward quantifying absolute changes in the global lightning activity on various timescales within the cavity.
Article
Sprite halos are brief, diffuse flashes, which occur at the top of a sprite and precede the development of streamer structures at lower altitudes. We have investigated the characteristics of sprite halos in detail using coincident photometric and imaging data obtained during the Sprites'96 and '99 campaign in Colorado and Wyoming, USA. It is found that the average altitude of the centroid of the halo emission and the mean horizontal diameter of the halo events are ∼80 and ∼86 km, respectively, while the average speed of the descending motion of the sprite halos was ∼4.3 × 107 m/s. It was also found that the peak current intensity of the causative CG decreases with time delay from the onset of the sferics.
Article
In order to elucidate the electrodynamic coupling process between sprites and their causative cloud-to-ground lightning discharges, we investigated 38 columniform sprite events observed in the wintertime sprite campaigns in Japan. By analyzing the data of sprite images, transient Schumann resonance waveforms and the JLDN/LPATS lightning detection network systems, we found that the number of columns in each sprite event was proportional to the peak current intensity of positive cloud-to-ground lightning discharges (+CGs) while the average vertical length of columns was proportional to the charge moment of the causative +CGs. Based on these results, we suggest that electromagnetic pulses (EMPs) radiated from +CGs contribute to the formation of seeds for sprite streamers while the QE field contribute to the development of the streamers from the seeds.
Article
Space-based instruments on the Tropical Rain Measuring Mission (TRMM) have been used to study rainfall and lightning over the central and eastern Mediterranean Sea. Data from six winters (1998 until 2003) were analyzed. Rainfall amounts increase during the winter months, with the maximum precipitation occurring during December, while lightning activity has a maximum during November. Analysis of seasonal rainfall and lightning activity showed a strong correlation with ENSO events. Instantaneous (90 second) analysis of the rain and lightning in individual storms reveals a strong correlation between rain rate and total flash rate. Monthly and seasonal correlation coefficients between rainfall and lightning were found to vary between 0.81 and 0.98, with the rainfall yield (kg/flash) found to vary between 2.5 × 108 and 9.7 × 108 kg/flash. Due to these high correlations we suggest the possibility to use lightning data over the Mediterranean Sea as a proxy for instantaneous rain rate in thunderstorms.
Article
We report synchronized optical observations of sprites in Israel during the winters of 2006/7–2007/8. Based on several events, we suggest that the elements of columniform sprites are organized in spaced intervals on the circumference of a circle centered directly above, or a little offset, to the vertical direction from the parent lightning. In 2D images most of the cases show columns to be arranged in highly eccentric elliptical forms or in straight rows. The analysis of the optical images provided the geometrical dimensions of the columns and their spatial organization. We used an electrostatic model of the QE field with reasonable assumptions on the location and magnitude of the cloud charge center, constrained by ELF evaluation of the Charge Moment Change in the parent flash, to show that the observed diameter of the columnar arrangement closely matches the conventional breakdown field line contour at the same altitude.
Article
This paper presents an overview of the recent modeling efforts directed to the interpretation of observed features of transient luminous events termed sprites, blue jets, and gigantic jets. The primary emphasis is placed on interpretation of various emissions documented to date from sprites and comparison of exiting models with recent high-speed video and satellite-based observations of sprites. We also discuss the recently advanced theories of blue jet and gigantic jet discharges describing electrodynamic conditions, which facilitate escape of conventional lightning leaders from thundercloud tops and their upward propagation toward the ionosphere. The paper concludes with a brief survey of the recent literature on chemical and global electric circuit effects of sprite and jet discharges.
Article
The occurrence of negative and positive ground flashes in Tel-Aviv, Israel (32.05 N, 34.45 E) has been monitored through daily registrations of a CGR3-SN5 lightning flash counter (Mackerras, 1985). Measurements were conducted from 1987 to 1995, with the most continuous data sets available for the period 1992-1995. The lightning data was augmented by radar measurements of the thunderclouds (starting from 1994) and by radiosonde data. It was found that the fraction R of positive lightning from the total ground flash count is highly variable, with a long-term average of 0.25. It is shown that storms having a relatively large value of R coincide with strong vertical shear of the horizontal wind component. The dependence of R on the intensity of the wind shear S in the cloud layer between the 0°C and -25°C isotherms, may be expressed by: logR=aS-b, where a=0.1504 and b=1.1471.
Article
The winter thunderclouds that frequently visit the southeastern coastal area of the Japan Sea were investigated by the field work, operating radars, the sferics direction-finder system, and the field-mill network. The clouds take the dipole electrical structure at their developing stage and then take the tripole structure at the mature stage. However, the period covering both dipole and tripole structures is very short (usually less than 10 min in early or late winter and less than several minutes in midwinter), because the graupel particles that carry the main negative charge and the lower positive charge do not satisfy stationarily in the clouds but fall off rapidly. For the remainder of the period of cloud duration, which lasts relatively long, the positive charge predominates in the clouds. The grade of charge separation and lightning activity is restricted by the altitude of -10°C temperature level. When the altitude is lower than 1.8 km, the clouds exhibit weak or no lightning activity. When it is lower than 1.4 km, the clouds exhibit neither natural lightning discharge nor tripole electrical structure.
Article
Continuous observations of sprites in the Hokuriku area of Japan were performed from two optical sites during the three winter periods. The purpose of this observation is to study the major effect in the appearance of sprites and in determining the morphology of sprites (columns or carrots). Detailed analysis is performed based on the estimation of the height of −10°C at the time of sprite occurrence. When the height of −10°C is lower than 1800m, the occurrence of sprites is infrequent, and the dominant shape is column. Then when it is increased (1800–3000m), a new situation takes place, namely the occurrence of sprites is very enhanced and more spectacular shapes like carrots tend to be frequently observed in addition to column sprites. These sprite characteristics are first compared with those of parent lightning in the Hokuriku area and with our latest computer simulations on sprite initiation.
Article
Sprites are large scale manifestations of electrical streamers triggered in the upper atmosphere by lightning in an underlying thunderstorm. Imaging of sprites at 10 000 frames per second has provided new insights into their spatial and temporal development. In this paper we discuss the experimental protocols that have been developed for performing high-speed observations of sprites and some new observations that have been obtained of relevance to laboratory experiments. Downward tendrils and upward branches, so characteristic in video recordings, are shown to be formed by very fast streamer heads with velocities up to half the speed of light. The streamer heads are spatially small, ~100 m or less, but very bright with emission rates up to ~1024 photons s−1. The sprite onset begins with a downward streamer. Then, in some sprites, at a little later time and from a lower altitude upward moving streamer heads may also appear. If there are no upward streamers the sprite would be classified as a 'C-sprite'; with both downward and upward streamers it would be a 'carrot sprite'. The optical emissions are primarily from the neutral molecular nitrogen first positive bands emitting in the near-infrared, but there are also blue emissions assumed to be from second positive bands of molecular nitrogen and from first negative bands of nitrogen ions. The streamer heads are observed at times to split into several streamer heads. This process appears to be more frequent in the core of larger sprites.