Flash Location Research Articles

The ventriloquist effect does not depend on the direction of deliberate visual attention.

It is well known that discrepancies in the location of synchronized auditory and visual events can lead to mislocalizations of the auditory source, so-called ventriloquism. In two experiments, we tested whether such cross-modal influences on auditory localization depend on deliberate visual attention to the biasing visual event. In Experiment 1, subjects pointed to the apparent source of sounds in the presence or absence of a synchronous peripheral flash. They also monitored for target visual events, either at the location of the peripheral flash or in a central location. Auditory localization was attracted toward the synchronous peripheral flash, but this was unaffected by where deliberate visual attention was directed in the monitoring task. In Experiment 2, bilateral flashes were presented in synchrony with each sound, to provide competing visual attractors. When these visual events were equally salient on the two sides, auditory localization was unaffected by which side subjects monitored for visual targets. When one flash was larger than the other, auditory localization was slightly but reliably attracted toward it, but again regardless of where visual monitoring was required. We conclude that ventriloquism largely reflects automatic sensory interactions, with little or no role for deliberate spatial attention.

Cloud‐to‐ground lightning activity and radar observations of storms in the pyrénées range area

AbstractThis paper analyses radar observations and cloud‐to‐ground (CG) lightning flash activity of several thunderstorms occurring over the Pyrénées range during the night of 23‐24 August 1993 and the afternoon of 24 August 1993. the available data consisted of the European meteorological bulletin, the plan position indicator radar scans at three elevations performed by the 5.5 cm wavelength Rodin radar of Toulouse, and the characteristics of the CG lightning strikes.The first thunderclouds began to develop at around 2200 UTC 23 August. Up to 0100 UTC 24 August, we observed three isolated convective cells. We also studied a mesoscale convective system (MCS) occurring during the afternoon of 24 August, and chose to investigate three convective cells embedded within it. These different thunderclouds developed over the Spanish side of the Pyrénées and moved north‐eastwards over the mountains. the locations of CG flashes in relation to the reflectivity fields revealed two kinds of CG lightning activity: flashes associated with intense rainfall, and those located in stratiform cloud areas far from the intense precipitating zone. the flash density was larger within the first type and the positive flash proportion was larger in the second type. the amount of large precipitating particles was characterized by the area A(τ) covered by reflectivities larger than τ dBZ, with τ taken as 33 dBZ. the study of the time evolution of A (33) at three altitudes showed that, for the lightning activity associated with intense rainfall, strong reflectivities at high altitude (4.5 km, and sometimes 7.5 km) coincided with large lightning flash rates, though it was the time evolution of the vertical profile of the area covered by precipitation that drove the CG lightning flash rate (or vice‐versa). the maximum flash rate coincided with the fall of large precipitating particles. Furthermore, a time lag was observed at the ground between the lightning flash rate and the rainfall rate. the time evolutions of the flash rate and A (τ) at the lowest elevation of the radar beam (0.6°) confirmed this delay. the correlation coefficient between these two parameters for the isolated convective cells reached 0.81 in the best case. the correlation between the lightning activity and precipitation of the whole MCS was less good but, nevertheless, the volume of precipitation per CG lightning flash was of the same order of magnitude for all the cells or MCSs observed. It ranged from 3.2 × 103 to 46.8 × 103 m3 flash‐1, in accordance with the results of other authors.

Thunderstorm Characteristics of Cloud-to-Ground Lightning at the Kennedy Space Center, Florida: A Study of Lightning Initiation Signatures as Indicated by the WSR-88D

Abstract The operational potential for predicting the onset of cloud-to-ground lightning is examined. WSR-88D reflectivity echoes were analyzed for 39 airmass thunderstorms that developed over the NASA Kennedy Space Center, Florida, to determine the best lightning initiation signature. This study examined thunderstorms in the months of May–September 1992–97. These storms were studied in conjunction with cloud-to-ground (CG) lightning flash locations from the National Lightning Detection Network. From a time series of radar echoes, it was found that the 40-dBZ echo detected at the −10°C temperature height is the best indicator for predicting the beginning of CG lightning activity. The observed median lag time, or warning time, between this lightning initiation signature and the first CG lightning flashes was 7.5 min. Other lightning initiation signatures examined at −15° and −20°C temperature heights yielded shorter warning times.

Convective Structure of Hurricanes as Revealed by Lightning Locations

Cloud-to-ground lightning flash locations were examined for nine Atlantic basin hurricanes using data from the National Lightning Detection Network. A common radial distribution in ground flash density was evident: a weak maximum in the eyewall region, a clear minimum 80–100 km outside the eyewall, and a strong maximum in the vicinity of outer rainbands (210–290-km radius). These results are consistent with the authors’ previous study of Hurricane Andrew. None of the storms showed this characteristic radial structure during prehurricane stages. The results support the division of precipitation in the hurricane into three distinct regimes. The eyewall is a unique phenomenon but shares some attributes with deep, weakly electrified oceanic monsoonal convection. The region outside the eyewall and under the central dense overcast has characteristics of the trailing stratiform region of mesoscale convective systems, including a relatively high fraction of positive polarity flashes. The outer bands, with mean maximum flash density at the 250-km radius, contain the vast majority of ground flashes in the storms. Eyewall lightning, defined as that within 40 km of the center, was examined for four moderate-to-strong hurricanes. Such lightning occurred episodically during hurricane stage, with 93% of hourly intervals containing no detected flashes. Eyewall lightning outbreaks over water always occurred at the beginning of or during times of intensification, but often were indicative of the imminent end of deepening. It is proposed that the existence of such inner core lightning might reveal the presence of an eyewall cycle. For the one storm with available aircraft reconnaissance data, eyewall cycles were reliably identified by the occurrence of inner core lightning, and inner core lightning appeared only during such cycles. Suggestions are made as to how eyewall flashes in existing hurricanes might be used to help predict hurricane intensity change.

The Diurnal Distribution of Lightning over North Florida and Its Relation to the Prevailing Low-Level Flow

Abstract Six years (1989–94) of cloud-to-ground lightning data are used to examine the distribution of lightning across the Florida panhandle and adjacent coastal waters and its relationship to the prevailing low-level flow. Only warm season data between 1 May and 31 October are used. The prevailing flow is determined by subdividing the low-level (1000–700 mb) vector mean wind into categories that are either parallel or perpendicular to various parts of the coastline. Moderate wind speeds (2–5 m s−1) generally are found to be more conducive to producing lightning than stronger speeds. Wind speeds stronger than 5 m s−1 likely inhibit the formation of the sea breeze, the main focus for summertime thunderstorms in the region. Onshore, offshore, and parallel flows are found to play important roles in determining the patterns of flash locations in each flow regime. The complexity of the coastline also is found to have a major impact on the flash distributions. The prevailing wind direction is shown to be relat...

Estimation of Convective Rainfall from Lightning Observations

Abstract The objective of this study is to develop a technique to use lightning observations for estimating convective rainfall. A framework for rainfall estimation is developed in which key elements are 1) the rainfall–lightning ratio, that is, the convective rainfall mass per cloud-to-ground lightning flash; 2) the spatial distribution of rainfall relative to flash locations; and 3) the temporal distribution of rainfall relative to the time of lightning occurrence. These three elements are examined through a study of 22 summer thunderstorms in the domain covered by the Melbourne, Florida, WSR-88D radar during August of 1992 and 1993. The analyses are carried out by combining lightning observations from the National Lightning Detection Network with storm parameters computed from 3D reflectivity observations using the Thunderstorm Identification Tracking and Nowcasting storm-tracking and analysis algorithms. The effect of the prevailing convective regime on the variability of lightning–rainfall relationsh...

Global radiolocation in the lower ELF frequency band

A system for recording large‐amplitude discrete extremely low frequency atmospherics (ELF “events” or “Q bursts”) produced by global lightning activity is described. The location of the source lightning flashes for some 261 events has been deduced from these data. In the data set, about 75% of the signals were produced by positive flashes and 25% were produced by negative flashes. The analysis technique depends on the fact that in the lower ELF band (5–45Hz), signals can be detected which have made multiple circulations of the globe. The range of the sources was found by modelling the data using a least squares fit to the complex wave impedance computed using the well‐established propagation theory applicable to the Earth‐ionosphere spherical‐shell waveguide. The source bearings were deduced from two orthogonal components of the magnetic field vector using the usual goniometric technique. The data show that the majority of the sources of ELF events are located in low‐latitude regions, an average of 7.4 Mm away from the observing station situated in the UK. The use of such a system to monitor worldwide thunderstorm activity, so far as this relates to ELF events observed in the band 5–45 Hz, is demonstrated.

Effects of aging on event-related brain potentials (ERPs) in a visual detection task

Event-related brain potentials (ERPs) were recorded from 74 subjects (45 men) between 18 and 82 years of age in a simple visual detection task. On each trial the subject reported the location of a triangular flash of light presented briefly 20° laterally to the left or right visual field or to both fields simultaneously. ERPs to targets exhibited a similar morphology including P1, N1, P2, N2, and P3 components across all age groups. The principal effects of advancing age were (1) a marked reduction in amplitude of the posterior P1 component (75–150 latency) together with an amplitude increase of an anterior positivity at the same latency; (2) an increase in amplitude of the P3 component that was most prominent over frontal scalp areas; and (3) a linear increase in P3 peak latency. These results extend the findings of age-related changes in P3 peak latency and distribution to a non-oddball task in the visual modality and raise the possibility that short-latency ERPs may index changes in visual attention in the elderly.

Anomalous Cloud-to-Ground Lightning in an F5-Tornado-Producing Supercell Thunderstorm on 28 August 1990

An F5 tornado that devastated Plainfield, Illinois, and environs on 28 August 1990, killing 29 people, is shown to be produced by a thunderstorm characterized by highly anomalous cloud-to-ground (CG) lightning activity. Unlike typical summertime convection in which the majority of CG flashes lower negative charge to ground, the Plainfield storm produced predominantly positive-polarity CG flashes during development. Changes in storm structure revealed by radar imagery appear tied to distinct patterns in the CG flash parameters of polarity, flash frequency, first stroke peak current, flash multiplicity, and flash location relative to the parent cumulonimbus. The primary findings are 1) the anomalous predominance (91%) of positive-polarity CG flashes during development; 2) positive CG flashes anomalously occurring mainly within the region of the storm's radar reflectivity core; 3) the onset of a major downburst coinciding with a sudden increase in CG flash rate, from 4 to 17 flashes min-1, and positive perce...

Calibration of a magnetic direction finding network using measured triggered lightning return stroke peak currents

Peak currents from 18 triggered lightning return strokes lowering negative charge have been measured at the NASA Kennedy Space Center, Florida. These strokes are correlated with simultaneous measurements by six Lightning Location and Protection (LLP) Inc. wideband magnetic direction finders (DFs) in Georgia and Florida operating at high gain from 1985 through 1988. The following have been determined: (1) The normalized signal strength amplitudes, in LLP units, can be used to estimate the peak current in lightning return strokes by the relation, I(kA) = 2.3+0.19(Normalized Amplitude), where the amplitude is range‐normalized to 100 km. An approximation of the form, I(kA) = 0. 2(Normalized Amplitude) is also valid, introducing errors of typically less than 6 %. (2) Range‐normalized signal strength amplitudes, in LLP units, for individual DFs have been examined as a function of the measured return stroke peak currents. It is found that a DFs normalized amplitude has a higher correlation with peak currents, the further the DF site is from the triggered lightning. The correlation coefficients range from 0.53 to 0.93, At a DF site the standard deviation of the normalized amplitudes from the best fit line to the measured peak currents are independent of the DF site's distance from the triggered lightning, averaging 28 LLP units, which corresponds to 6 kA. (3) Signal strength amplitudes, which are proportional to the peak magnetic radiation fields, have been examined for seven triggered lightning return strokes. The signal strength amplitudes decay with distance, D, as D−1.13. (4) An evaluation of the error in the mean range‐normalized signal strength amplitude caused by lightning location errors reveals that the mean amplitude is typically in error by less than 2% from the value calculated using the exact location of the triggered flash.

Decision criteria for computer-aided parting surface design

A scientific approach is presented and the related logic developed for design of parting surfaces of patterns, moulds and dies used in the manufacture of cast, forged, injection-moulded and die-cast components. This has enabled computer-aided generation of parting surfaces and the determination of projected area, flatness and draw for a parting surface, identification of surfaces to which draft is provided, recognition of component segments causing undercuts, testing for dimensional stability, and location of flash, machined surfaces and feeders. Influencing criteria for parting-surface design have been formulated and developed into algorithms implemented on a personal computer. This approach greatly aids the engineer in rational decision making, paving the way for a systemized code for parting-surface design.

Peak-current variations of lightning return strokes as a function of latitude

LATITUDINAL variations in lightning-flash characteristics have been hypothesized1,2, but have not been found to exist3,4. This may be because lightning characteristics are constant over the Earth, or because the observations have been made over too small an area of the globe. To investigate the question of latitudinal variation, I have used a network of thirty-six gated wideband magnetic direction finders covering the eastern United States to measure the characteristics of cloud-to-ground lightning flashes. These characteristics include the flash location, the flash polarity, the number of strokes in the flash and the peak magnetic radiation field in the first return stroke of the flash. From the peak radiation field, I estimate the peak current5. More than five million lightning ground flashes were recorded by the network in 1988. An examination of the mean peak current in the first return stroke shows that the peak current varies by almost a factor of two, from 25k A in New England to 40–45 kA in northern Florida. Apparently, this is the first report of an important lightning parameter, the return stroke current, varying over a large area of the globe. It seems that the generation of lightning strokes and their characteristics may be a sensitive function of latitude and hence of temperature. The results presented here indicate that even higher peak currents will be observed if this research is extended into the equatorial regions.

A parametric estimation of systematic errors in networks of magnetic direction finders

We consider the problem of estimating systematic errors in a network of magnetic direction finders using bearing data from a historical record containing a large number of lightning flash observations. It is clear that this problem is linked with the flash location estimation problem and that the two are statistically confounded in the sense that the effect of one cannot be separated from the other. We formalize mathematically a connection between the two problems to arrive at a self‐consistent system. In this paper we parameterize the site errors as two‐cycle sinusoidal functions and show that the estimation equations can be described by a model which separates into linear and nonlinear parameters. We take advantage of this separation to decouple large‐dimensional equations into smaller dimensional equations. Through these equations we show the link between the site error and flash location estimation problems. Validation of our modeling procedures is done by heuristic arguments and analysis of residuals. The latter reveals that not all of the residuals have been explained by sinusoidal site errors but that some residuals might result from the geometry of the network. This appears to be an important problem and is presently under study. Also, there is a need to test the site error estimation algorithm developed in this paper against some ground truth.

Ground truth confirmation and theoretical limits of an experimental VLF arrival time difference lightning flash locating system

During trials of a VLF Arrival Time Difference (ATD) technique for long range lightning flash location, an apparently well organized and isolated flash sequence was located. Internal ATD evidence suggests flashes were located at a thousand-kilometre range to within 5 km. ‘Ground truth’ based on synoptic/mesoscale considerations, observer reports, and lightning damage claims confirms locations to 10–15 km. In addition, elimination of systematic effects from internal ATD evidence demonstrates relative flash location errors of 0.9-1.8 km, and a ‘tight cluster’ of ATD fixes features scatter in location which is not inconsistent with these values. The nature of VLF lightning flash observation is examined, and shown to be consistent with errors even smaller than this.

Ground truth confirmation and theoretical limits of an experimental VLF arrival time difference lightning flash locating system

AbstractDuring trials of a VLF Arrival Time Difference (ATD) technique for long range lightning flash location, an apparently well organized and isolated flash sequence was located. Internal ATD evidence suggests flashes were located at a thousand‐kilometre range to within 5 km. ‘Ground truth’ based on synoptic/mesoscale considerations, observer reports, and lightning damage claims confirms locations to 10–15 km. In addition, elimination of systematic effects from internal ATD evidence demonstrates relative flash location errors of 0.9‐1.8 km, and a ‘tight cluster’ of ATD fixes features scatter in location which is not inconsistent with these values. The nature of VLF lightning flash observation is examined, and shown to be consistent with errors even smaller than this.

The Limiting Accuracy of Long Wavelength Lightning Flash Location

Abstract Many recently developed systems for lightning flash location use frequencies of hundreds of kHz or higher to achieve enhanced precision, although this reduces potential range. However, for coherent systems operating at high signal-to-noise ratios VLF observing frequencies can reduce the target to a “point image” with typical horizontal dimensions of 10 m or less, potentially reducing relative location errors. Absolute location errors are larger, but may be below 1 km for a well calibrated system. Thus there is no fundamental conflict between potential aims of precision in flash location and long range. A typographical error in Lin et al.'s description of their lightning return stroke model is reported.

A method for examining gestural language structure.

This experiment tested the hypothesis that syntactic constituents in American Sign Language (ASL) serve as perceptual units. We adapted the strategy first employed by Fodor and Bever in 1965 in a study of the psychological reality of linguistic speech segments. Four deaf subjects were shown ASL sign sequences constructed to contain a single constituent break. The dependent measure was the subjective location of a light flash occurring during the sign sequence. The prediction that the flashes would be attracted to the constituent boundary was supported for two of the subjects, while the other two showed random placement of the flash location on either side of the constituent boundary. The two subjects not performing in the predicted direction were more proficient in English (written) than the two giving the effect. It was suggested that this relatively greater proficiency may have interfered in some way with the ASL syntax to produce the results obtained.

An Operational System for the Remote Location of Lightning Flashes Using a VLF Arrival Time Difference Technique

Abstract An operational system for the remote location of lightning flashes at ranges of thousands of kilometers is presented. The vertical electric fields of VLF radio atmospherics (sferics), together with time data, are observed at a network of just seven outstations dispersed over the United Kingdom and the Mediterranean. These data are forwarded to a control station, which locates individual flashes in real time using arrival time difference (ATD) techniques, analogous to Loran-C, and generates regular reports for automatic distribution. The service area covered exceeds 30° to 70°N, 40°W to 40°E; flash location accuracy is 2-20 km; and approximately 400 flashes per hour can be located.

An experimental study of the remote location of lightning flashes using a VLF arrival time difference technique

AbstractThe operational ‘cathode ray direction finding’ (CRDF) network for the location of lightning flashes at ranges up to thousands of kilometres can be replaced by a system using the ‘arrival time difference’ (ATD) technique. The ATD technique has theoretical advantages over CRDF, which could lead to substantially improved flash location, but the extent to which it suffers from certain propagation effects in practice must be quantified.In an experiment using the ATD technique, equipments were deployed in the U.K. and Gibraltar. These captured the vertical electric field of VLF electromagnetic radiation from individual lightning flashes, synchronized to CRDF‐selected flashes and recorded against an accurate timebase. By analysing the data using techniques analogous to those of hyperbolic navigation, the flash location was inferred, together with a measure of the data consistency.ATD location of independent flashes observed in time proximity frequently gave the tight grouping expected from an isolated active thunderstorm cell. Groups of diameter 2–10 km were observed at megametre ranges.ATD flash locations were compared with CRDF and other meteorological data. Positioning agreed within the limited accuracy of current techniques, but the CRDF system's potential for poor accuracy was highlighted.An analysis method was developed relating the internal consistency of the ATD flash data to geographical location accuracy, and ATD accuracy of less than 5 μs was measured experimentally. On this basis, an ATD system can locate flashes over a synoptic‐scale area with errors comparable with a storm cell diameter.

The East Coast Lightning Detection Network

A magnetic direction-finding network for the detection of lightning cloud-to-ground strikes has been installed along the east coast of the United States. Most of the lightning occurring from Maine to Florida and as far west as Ohio is detected. Time, location, flash polarity, stroke count, and peak signal amplitude are recorded in real time. Flash locations, time, and polarity are displayed routinely for research and operational purposes. Flash density maps have been generated for the summers of 1983 and 1984, when the network only extended to North Carolina, and show density maxima in northern Virginia and Maryland. Computer-based display systems that access this network in real time are now in use to evaluate the usefulness of the data.