Flash Location Research Articles

The characteristics of cloud-to-ground lightning activity in hailstorms over northern China

The characteristics of cloud-to-ground (CG) lightning for ten hailstorms in Shandong Province of China were analyzed statistically. It is found that the hailstorms in this study present dominant positive CG flashes during periods of falling hail. One specific hailstorm on 16 June 2006 was studied in detail using the data from a CG lightning location network, Doppler radar and cloud images. Comparison between the brightness temperature of cloud-top and CG flash locations indicated that most flashes occurred in the region with temperatures lower than − 40 °C, while dense positive CG flashes occurred in the range between − 40 °C and − 50 °C. Negative CG flashes occurred mostly in the relative weak radar echo region, and positive CG flashes were distributed in the strong echo region especially with a large gradient of echo intensity. CG flashes tended to occur in the cloud region with reflectivity between 25 dBZ and 35 dBZ. Comparison between the wind field retrieved from Doppler radar and the location of CG flashes indicated that the flashes were located in the convergent region at lower to middle levels.

Properties of preliminary breakdown processes in Scandinavian lightning

Lightning flashes are usually preceded by preliminary breakdown processes (PBPs) before a stepped leader is initiated. These breakdown processes are not well understood. An early model, the so-called BIL model, has been called into question in later studies. However, we have found that the BIL model is quite successful in describing initial processes at least in high-latitude Scandinavian lightning. We present results from one summer of measurements in Finland, during which the vertical electric field was measured with a standard broadband plate antenna system. Lightning flash locations were provided by a lightning detection network and magnetic fields were measured with an experimental narrowband detection system. The relationship between the preliminary breakdown and the first return stroke (RS) is studied for 193 flashes at distances of 5–70 km. We can identify a preliminary breakdown in at least 90% of the flashes. The peak electric field of the RS is on average four times as intensive as the highest peak of the PBP. However, in 25% of the cases the PBP peak is more intensive. On the other hand, we show that this method of comparing intensities is physically arbitrary, since the PBP is continuous and the RS is impulsive. The narrowband measurement allows a physically consistent definition for intensities as the root-mean-square (RMS) sum of the most intense parts of signals. The PBP and RS are shown to have almost equal intensities at small distances. At larger distances, the PBP weakens more rapidly. This is suggested to be due to different propagation regimes, with the PBP signal changing from space-wave to ground-wave propagation with increasing distance, while the RS is predominantly ground wave at all distances. The result may have practical applications in narrowband detection of lightning. The BIL model suggests a characteristic signal in the narrowband signal, which could be used to identify the start of a lightning flash. The change in the RS–PBP ratio as a function of distance is statistically significant, but is too weak to significantly improve ranging methods.

Changing Reference Frames during the Encoding of Tactile Events

The mindless act of swatting a mosquito on the hand poses a remarkable challenge for the brain. Given that the primary somatosensory cortex maps skin location independently of arm posture [1, 2], the brain must realign tactile coordinates in order to locate the origin of the stimuli in extrapersonal space. Previous studies have highlighted the behavioral relevance of such an external mapping of touch, which results from combining somatosensory input with proprioceptive and visual cues about body posture [3-7]. However, despite the widely held assumption about the existence of this remapping process from somatotopic to external space and various findings indirectly suggesting its consequences [8-11], a demonstration of its changing time course and nature was lacking. We examined the temporal course of this multisensory interaction and its implications for tactile awareness in humans using a crossmodal cueing paradigm [12, 13]. What we show is that before tactile events are referred to external locations [12-15], a fleeting, unconscious image of the tactile sensation abiding to a somatotopic frame of reference rules performance. We propose that this early somatotopic "glimpse" arises from the initial feed-forward sweep of neural activity to the primary somatosensory cortex, whereas the later externally-based, conscious experience reflects the activity of a somatosensory network involving recurrent connections from association areas.

Using full-flash narrowband energy for ranging of lightning ground strokes

We demonstrate that narrowband measurements can be used for rudimentary ranging of cloud-to-ground lightning flashes. The system at present responds to both intra-cloud and cloud-to-ground lightning; ranging is demonstrated for a subset of flashes known to be cloud-to-ground lightning. The system uses a ferrite-core antenna with a length of about 4 cm and diameter 4 mm, and operates on a narrow band at about 1 MHz, close to the HF band (3–30 MHz). It downmixes the signal to audio frequencies and operates in a manner which is very similar to an AM radio. The system triggers on all impulses which exceed a given adjustable threshold above the ambient noise level, and records 1 s of data. Such a system was used to collect lightning-caused electromagnetic disturbances during summer 2006 in Finland. The output is compared to two scientifically verified references: a flat-plate broadband antenna measuring the vertical electric field and a commercial lightning location network giving flash location. A key aim of the system is to reduce the information to as few parameters as possible. Peak intensity and full-flash energy were used as simple parameters. It is shown that accurate flash-by-flash ranging is not possible with this method; however, it is shown that the method can be used to track clusters of ground flashes within a range of about 50–100 km with an accuracy of about 10 km.

A model of the mechanism for the perceived location of a single flash and two successive flashes presented around the time of a saccade

According to current accounts, the perceived location of a target flash presented in the dark around the time of a saccade comes largely from an extraretinal signal that begins to change before, and continues to change during and following the saccade. Opposed to this view, this study offers a model suggesting that the perception of a single flash or two successive flashes in association with a saccade is the result of the combined effects of flash retinal signal persistence and an extraretinal signal that begins concurrent with or shortly after the saccade. For a single flash, the retinal signal persistence interacting with the extraretinal signal is responsible for the perceived location of the flash. In the case of two flashes with a short inter-flash-interval, the temporal overlap of the first flash persistence with the second flash persistence is a major factor in determining the perceived location of both of the flashes, and as a consequence, the perceived separation between them.

Electrical and Polarimetric Radar Observations of a Multicell Storm in TELEX

Abstract On 28–29 June 2004 a multicellular thunderstorm west of Oklahoma City, Oklahoma, was probed as part of the Thunderstorm Electrification and Lightning Experiment field program. This study makes use of radar observations from the Norman, Oklahoma, polarimetric Weather Surveillance Radar-1988 Doppler, three-dimensional lightning mapping data from the Oklahoma Lightning Mapping Array (LMA), and balloon-borne vector electric field meter (EFM) measurements. The storm had a low flash rate (30 flashes in 40 min). Four charge regions were inferred from a combination of LMA and EFM data. Lower positive charge near 4 km and midlevel negative charge from 4.5 to 6 km MSL (from 0° to −6.5°C) were generated in and adjacent to a vigorous updraft pulse. Further midlevel negative charge from 4.5 to 6 km MSL and upper positive charge from 6 to 8 km (from −6.5° to −19°C) were generated later in quantity sufficient to initiate lightning as the updraft decayed. A negative screening layer was present near the storm top (8.5 km MSL, −25°C). Initial lightning flashes were between lower positive and midlevel negative charge and started occurring shortly after a cell began lofting hydrometeors into the mixed phase region, where graupel was formed. A leader from the storm’s first flash avoided a region where polarimetric radar suggested wet growth and the resultant absence of noninductive charging of those hydrometeors. Initiation locations of later flashes that propagated into the upper positive charge tracked the descending location of a polarimetric signature of graupel. As the storm decayed, electric fields greater than 160 kV m−1 exceeded the minimum threshold for lightning initiation suggested by the hypothesized runaway breakdown process at 5.5 km MSL, but lightning did not occur. The small spatial extent (≈100 m) of the large electric field may not have been sufficient to allow runaway breakdown to fully develop and initiate lightning.

Numerically Simulated Electrification and Lightning of the 29 June 2000 STEPS Supercell Storm

Abstract A three-dimensional dynamic cloud model incorporating airflow dynamics, microphysics, and thunderstorm electrification mechanisms is used to simulate the first 3 h of the 29 June 2000 supercell from the Severe Thunderstorm Electrification and Precipitation Study (STEPS). The 29 June storm produced large flash rates, predominately positive cloud-to-ground lightning, large hail, and an F1 tornado. Four different simulations of the storm are made, each one using a different noninductive (NI) charging parameterization. The charge structure, and thus lightning polarity, of the simulated storm is sensitive to the treatment of cloud water dependence in the different NI charging schemes. The results from the simulations are compared with observations from STEPS, including balloon-borne electric field meter soundings and flash locations from the Lightning Mapping Array. For two of the parameterizations, the observed “inverted” tripolar charge structure is well approximated by the model. The polarity of the ground flashes is opposite that of the lowest charge region of the inverted tripole in both the observed storm and the simulations. Total flash rate is well correlated with graupel volume, updraft volume, and updraft mass flux. However, there is little correlation between total flash rate and maximum updraft speed. Based on the correlations found in both the observed and simulated storm, the total flash rate appears to be most representative of overall storm intensity.

Attentive tracking shifts the perceived location of a nearby flash

Several studies have shown that the perceived position of a briefly presented stimulus can be displaced by nearby motion or by eye movements. We examined whether attentive tracking can also modulate the perceived position of flashed static objects when eye movements and low-level motion are controlled. Observers attentively tracked two target bars 180° apart on a rotating, 12-spoke radial grating and judged the alignment of two flashes that were briefly presented, one on each side of the grating. Because of the symmetry of the 12-spoke grating, test flashes could be timed so that the rotating grating was always aligned to a standard orientation at the time of the test, while the tracked bars themselves, being only two of the 12 spokes, could probe locations that differed by multiples of 30° ahead of, aligned with, or behind, the test bars. Despite the physical identity of the stimulus in each test—same orientation, same motion—the perceived position of the two flashes strongly depended on the locus of attention: when the test flashes were presented ahead of the tracked bars, a large position shift in the direction of the grating’s motion was seen. If they were presented behind the tracked bars, the illusory displacement was reduced or slightly reversed. These effects of attention led us to suggest an attentional model of position distortions that links the effects seen for motion and for eye movements.

Identification and analysis of flash cells in thunderstorms

The convection-cell structure of a thunderstorm, often visible in the precipitation pattern of weather radar images, can also be identified in the clustering of ground flashes when their rate is high enough. The flashes can be grouped into cells with a set of rules applied to the time-ordered sequence of flash locations. A flash is associated with a group (cell) of older flashes if its distance and time lag are short enough, and some auxiliary conditions are fulfilled. With a careful choice of parameters the grouping algorithm, called Cellsearch, is able to resolve the flashes of a thunderstorm into a reasonable collection of ‘flash cells’ showing appropriate sizes, lifetimes and movements. The unavoidable occurrence of stray flashes, either true or caused by inaccurate locations, makes it necessary to reject some flashes from the cells and emphasize those in the cell core. All moderate-and high-activity thunderstorms in Finland during 1998–2002 are analysed for their flash-cell properties, and some representative cases are studied more closely. Copyright © 2005 Royal Meteorological Society

NO x ground concentration at a station at high altitude in relation to cloud-to-ground lightning flashes

Concentrations of both nitrogen oxides (NO x =NO+NO 2) observed at a station at high altitude (Puy de Dome (PDD), 1465 m) have been analyzed in relation with the cloud-to-ground (CG) lightning activity provided by the detection network Météorage. A first analysis of the time series of both types of data issued for 4 months of the 2003 summer shows a good correspondence between high values of NO x and stormy conditions in the area. During this 4-month period, NO x values exceeding 100 μg m −3 have been observed on 7 days and all of these days correspond to lightning activity in a 200×200 km 2 area around PDD. Thirty-three days of the period experience lightning activity in this area, and only 14 of these days (42%) correspond to NO x peak values exceeding 50 μg m −3. The presence of lightning activity is a necessary condition to have very large peak values of NO x at PDD, but this condition is not sufficient. Two days showed NO x exceeding 300 μg m −3 which represents a value between 176 and 270 ppbv according to the respective proportion of NO 2 and NO. Six days are analyzed in detail, using other information about the convective system and the wind conditions. The data of urban stations close to PDD have also been considered in the analysis for evaluating the possible transport by a plume from a city area. These days include the higher NO x cases, cases with high lightning activity, and cases with remote lightning activity. On each of these days, the location of the CG flashes, the time delays between lightning activity and NO x increase, and the air flow seem consistent with an interpretation of NO x produced by lightning. The higher values of NO x correspond with close and stationary thunderstorms which produced large proportions of positive CG flashes with low wind conditions. However, the characteristic increase seems to depend on several parameters of the CG flashes: their rate, location, and polarity. By comparing with the values given by other authors for aircraft measurements at altitude, our observations indicate that large quantities of NO x could be produced by the CG flash processes.

A demonstration of the capabilities of multisatellite observations of oceanic lightning

We have examined lightning flashes in five nighttime, oceanic thunderstorms, which were jointly observed by Tropical Rainfall Measuring Mission (TRMM) and Fast On‐Orbit Recording of Transient Events (FORTE). The multiplicity of instruments on board these satellites presents a multiphenomenological snapshot view of oceanic nighttime convection. Data are available for five oceanic storms with a total of 40 flashes. The independent optical imagers on each satellite establish the flash locations. The relative fraction of Lightning Imaging Sensor (LIS)–detected optical pulses that were also observed by the FORTE/photodiode detector varied from 0% for LIS range less than 104 J sr−1 m−2 μm−1 to 100% for LIS range greater than 106 μJ−1 sr−1 m−2 μm−1. The FORTE/VHF data sometimes allow estimation of the VHF source emissions heights and identification of individual discharge processes as positive or negative, in‐cloud or cloud‐to‐ground. These observations reinforce the concepts that the VHF pulses are produced by a breakdown process, while the optical pulses are the result of current flow.

Models of the mechanism underlying perceived location of a perisaccadic flash

A variety of experiments have shown that subjects tend to perceive a target flash as mislocalized when the flash is presented just before, during or shortly after the occurrence of a saccade. The characteristics of this mislocalization suggest that it arises from an anticipatory, slow extraretinal signal, i.e., the signal starts to change before a saccade and continues to change during and after the saccade. However, a target flash creates a visual signal that can persist for as long as 300 ms. Interaction of this visual persistence with the extraretinal signal could have a significant influence on the perceived location of the target flash, and thus on features of the extraretinal signal as inferred from the perceived location. In this study, several different types of models were used to explore how retinal signal persistence together with an extraretinal signal might affect perception. According to these models, the anticipatory, slow extraretinal signal may be an artifact of using a target flash, and the actual extraretinal signal may begin to change only after saccade onset and relatively quickly.

Statistical analysis of space–time relationships between sprites and lightning

We present a detailed statistical analysis of the association of 40 sprite events with lightning from the parent thunderstorm. Both temporal and spatial criteria were used to identify the parent cloud-to-ground (CG) lightning. Sprite images were GPS time stamped and their locations triangulated. In contrast to previous reports of nearly one-to-one association of sprites with positive cloud-to-ground (+CG) lightning, 11 events (27%) did not have a +CG recorded by the National Lightning Detection Network (NLDN), and 7 events (17%) had neither NLDN nor very low frequency (VLF) signatures associated with them. A negative cloud-to-ground (−CG) preceded one of these events by 9 ms . As expected for ∼16.7 ms integrated images, none of the sprites without a +CG had any discernible visual characteristic that would distinguish them from “regular positive sprites”. We have calculated the distribution of time intervals (Δ t= t sprite− t lightning) for the sprites that had a parent +CG flash registered by the NLDN or VLF systems, and the distribution of distances between the sprite nadir positions and the flash locations registered by the NLDN. The time interval (Δ t) distribution had a peak around 10– 20 ms and a mean of 30 ms (total). This distribution is broadly consistent with the characteristic single electron avalanche time scale associated with streamer growth between ∼70 and 85 km . The distribution of the distances (Δ s) between the nadir point of sprites and the parent +CGs showed that approximately two-thirds of the sprites occurred within 50 km lateral displacement from the parent +CG. The parent +CG peak current distribution had a maximum at 40– 50 kA and mean of 60 kA , suggesting that high peak currents (I⩾75 kA) are not a necessary prerequisite for sprites. The peak current distribution for all +CGs of the storm, with a maximum around 10– 20 kA and mean of 27 kA , exhibits a qualitatively different form from the peak current distribution of the parent +CGs producing sprites.

The Effects of Vertical Wind Shear on the Distribution of Convection in Tropical Cyclones

The influence of vertical wind shear on the azimuthal distribution of cloud-to-ground lightning in tropical cyclones was examined using flash locations from the National Lightning Detection Network. The study covers 35 Atlantic basin tropical cyclones from 1985–99 while they were over land and within 400 km of the coast over water. A strong correlation was found between the azimuthal distribution of flashes and the direction of the vertical wind shear in the environment. When the magnitude of the vertical shear exceeded 5 m s−1, more than 90% of flashes occurred downshear in both the storm core (defined as the inner 100 km) and the outer band region (r = 100–300 km). A slight preference for downshear left occurred in the storm core, and a strong preference for downshear right in the outer rainbands. The results were valid both over land and water, and for depression, storm, and hurricane stages. It is argued that in convectively active tropical cyclones, deep divergent circulations oppose the vertical wind shear and act to minimize the tilt. This allows the convection maximum to remain downshear rather than rotating with time. The downshear left preference in the core is stronger for hurricanes than for weaker tropical cyclones. This suggests that the helical nature of updrafts in the core, which is most likely for the small orbital periods of hurricanes, plays a role in shifting the maximum lightning counterclockwise from updraft initiation downshear. The downshear right maximum outside the core resembles the stationary band complex of Willoughby et al. and the rain shield of Senn and Hiser. The existence and azimuthal position of this feature appears to be controlled by the magnitude and direction of the vertical wind shear.

A study of the relationship between cloud-to-ground lightning and precipitation in the convective weather system in China

Abstract. In this paper, the correlation between cloud-to-ground (CG) lightning and precipitation has been studied by making use of the data from weather radar, meteorological soundings, and a lightning location system that includes three direction finders about 40 km apart from each other in the Pingliang area of east Gansu province in P. R. China. We have studied the convective systems that developed during two cold front processes passing over the observation area, and found that the CG lightning can be an important factor in the precipitation estimation. The regression equation between the average precipitation intensity (R) and the number of CG lightning flashes (L) in the main precipitation period is R = 1.69 ln (L) - 0.27, and the correlation coefficient r is 0.86. The CG lightning flash rate can be used as an indicator of the formation and development of the convective weather system. Another more exhaustive precipitation estimation method has been developed by analyzing the temporal and spatial distributions of the precipitation relative to the location of the CG lightning flashes. Precipitation calculated from the CG lightning flashes is very useful, especially in regions with inadequate radar cover.Key words. Meteorology and atmospheric dynamics (atmospheric electricity; lightning; precipitation)

Effects of inter-stimulus interval on perceived locations of successively flashed perisaccadic stimuli

We investigated the perceived locations of two stimuli flashed successively near the time of saccade execution in a dark room. The inter-stimulus interval (ISI) between the flashes ranged from 80 to 240 ms. The results show that when the ISI was 120 ms or shorter, perceived locations of the flashes interacted with each other so that the perceived distance between them was equal to the distance between these flashes on the retina. When the ISI was 240 ms, this interaction was weak. These results suggest two hypotheses. Firstly, the relation of retinal locations of flashes is a strong cue for perceiving the flash locations when the ISI is shorter than about 120 ms. Secondly, the process of perceiving or memorizing a flash location requires some time. Therefore, the perceived location of the succeeding flash affects that of the preceding flash when the ISI as shorter than about 120 ms.

A Lightning Parameterization for Numerical Cloud Models

Abstract A new lightning parameterization has been developed to enable cloud models to simulate the location and structure of individual lightning flashes more realistically. To do this, three aspects of previous parameterizations have been modified: 1) To account for subgrid-scale variations, the initiation point is chosen randomly from among grid points at which the electric field magnitude is above a threshold value, instead of being assigned always to the grid point having the maximum electric field magnitude. 2) The threshold value for initiation can either be constant, as in previous parameterizations, or can vary with height to allow different flash initiation hypotheses to be tested. 3) Instead of stopping at larger ambient electric field magnitudes, extensive flash development can continue in regions having a weak ambient electric field but a substantial charge density. This behavior is based on lightning observations and conceptual models of lightning physics. However, like previous parameteriza...

Perception of relation of stimuli locations successively flashed before saccade

Based on localization error for a single perisaccadic flash, eye position signal is supposed to change more slowly than physical eye position. Nevertheless, a flicker is not perceived as moving in accordance with localization error for a single flash. We carried out two experiments to investigate this problem. Experiment 1 examined how a single flash or a flicker presented before saccade was perceived. The results showed that the flicker was not perceived as moving, although mislocalization for the single flash increases gradually before saccade. Experiment 2 was a vernier test of two stimuli successively flashed before the saccade. The results showed that the point of subjective equality shifted in accordance with the mislocalization for a single perisaccadic flash when the interstimulus interval (ISI) was about 2 s; however, it did not shift when the ISI was 78 ms. Comparison between these results and previous studies suggests that the relation of the locations of successive flashes before saccade is perceived exocentrically when the ISI and stimulus onset asynchrony between flashes was short.

The global distribution of lightning NOx simulated on-line in a general circulation model

In this work, a time dependent lightning emission of nitrogen oxides is introduced in the LMDz general circulation model coupled to the chemistry module INCA using parameterizations for flash location and occurrence, lightning type, NO production per flash and vertical distribution. Major features of observed lightning activity are reproduced by the model as the seasonal cycle and the diurnal variation. Absolute simulated flash frequencies, however, are underestimated compared to observations from the Optical Transient Detector. Sensitivity studies are performed in order to better constrain the source of NOx by lightning. When the global lightning source is scaled to 5 TgN/yr, with vertical profiles specified according to Pickering et al. (1998), simulated concentrations of NO agree well with measurements made by Ridley et al. (1994) during the ELCHEM campaign. We confirm that lightning represents the main source of nitrogen in the tropical upper troposphere and contributes significantly to the total NOx field at northern midlatitudes in summer (20—30 percent). Aircraft emissions provide 5–35 percent of the total NOx in the upper troposphere at northern midlatitudes.

Electric‐field changes of lightning observed in thunderstorms

During the Summer and Fall of 1998 we launched five balloon‐borne instruments into thunderstorms to observe changes in the vertical component of electric field caused by lightning. Four of these were for measurement of field change only. The fifth was part of a larger package that included a gamma radiation detector and a GPS receiver on board. We have processed electric‐field‐change data from two of these flights. We discuss examples of field changes observed at altitude and compare them with data from the National Lightning Detection Network (NLDN) for cloud‐to‐ground lightning flashes that were coincident in time. Limits on time resolution and timing accuracy prevent unambiguous identification of the lightning processes that caused the field changes. It appears that they may have been caused by charge movements relatively near the instruments as compared with the ground‐strike location of coincident flashes.