Individual Flashes Research Articles

Global lightning acquisition system installed

A global network of seven time‐synchronized, high‐precision magnetometers around the world is ready to triangulate individual lightning flashes on planet Earth to monitor the temporal and spatial evolution of global lightning activity.This global network of magnetometers is able to detect the electromagnetic radiation of distant lightning flashes and makes possible remote sensing of the temporal evolution and spatial migration of global lightning activity [Füllekrug and Constable, 2000]. These results have led to international interest in a new measurement campaign with a large network of high‐precision magnetometers. The magnetic field changes are measured with ∼10‐14 Tesla accuracy (which corresponds to ∼10‐7% of the main geomagnetic field). The Global Positioning Satellites (GPS) provide time alignment of 0.00002 seconds between two measurement stations at antipodal distances (20×103, km), and the digital equipment makes possible continuous, high‐frequency recordings with 2000 samples per second.

Global triangulation of intense lightning discharges

A global network of three electromagnetic measurement instruments is used to simultaneously record time series of globally observable Extremely‐Low‐Frequency (ELF) magnetic field disturbances which propagate with little attenuation around the globe within the Earth‐ionosphere cavity. The triangulation of individual lightning flashes results in a picture of the temporal evolution of intense lightning discharge occurrences on the planetary scale during April 1998. The lightning flash charge moments are calculated with the short pulse approximation of the normal mode expansion. The majority of the triangulated lightning discharges exhibit charge moments with a potential to excite mesospheric sprites and ∼5–20% may account for air breakdown at sprite altitudes in ∼50–70 km height.

NO signatures from lightning flashes

In situ measurements of cloud properties, NO, and other trace gases were made in active thunderstorms by two research aircraft. Concurrent measurements from a three‐dimensional (3‐D) VHF interferometer and the 2‐D National Lightning Detection Network were used to determine lightning frequency and location. The CHILL Doppler radar and the NOAA‐WP‐3D Orion X band Doppler radar were also used to measure storm characteristics. Two case studies from the (STERAO) Stratosphere‐Troposphere Experiments: Radiation, Aerosols, and Ozone project in northeastern Colorado during the summer of 1996 are presented. Narrow spikes (0.11–0.96 km across), containing up to 19 ppbv of NO, were observed in the storms. Most were located in or downwind of electrically active regions where the NO produced by lightning would be expected. However, it was difficult to correlate individual flashes with NO spikes. A simple model of the plume of NO from lightning is used to estimate NO production from the mean mixing ratio measured in these spikes. The estimates range from 2.0×1020 to 1.0×1022 molecules of NO per meter of flash length.

Initial comparison of lightning mapping with operational time‐of‐arrival and interferometric systems

The mapping of lightning radiation sources produced by the operational Time‐of‐Arrival National Aeronautics and Space Administration/Lightning Detection and Ranging (NASA/LDAR) system is compared with that of the Interferometric French Office National D'Etudes et de Recherches Aerospatiales (ONERA‐3D) system. The comparison comprises lightning activity in three Florida storms and also individual flashes in one of these storms. Although limited in scope, the comparison and analysis show a significant difference in the representation of lightning radiation by each mapping system. During the duration of a flash, the LDAR data show a continuity in time and a three‐dimensional structure of radiation sources. The ONERA‐3D radiation source data are more intermittent in time and have a more two‐dimensional structure. The distinction between the radiation sources mapped by the two systems is also reflected in the difference between their propagation speeds, 104–105 m s−l, estimated by the LDAR system, and 107–108 m s−1, estimated by the ONERA‐3D system. We infer that this difference occurs because most of the radiation sources mapped with LDAR are associated with virgin breakdown processes typical of slowly propagating negative leaders. On the other hand, most of the radiation sources mapped with ONERA‐3D are produced by fast intermittent negative breakdown processes typical of dart leaders and K changes as they traverse the previously ionized channels. Thus each operational system may emphasize different stages of the lightning flash, but neither appears to map the entire flash.

Independently Acting Oxygen-Forming Complexes of Photosystem II in Cyanobacteria A Study in the Filamentous Cyanobacterium Oscillatoria chalybea

Abstract It has been postulated that the oxygen-evolving centers of photosystem II do not operate independently in the cyanobacterium Synechococcus leopoliensis in contrast to those of the chlorophyte Chlorella vulgaris and the diatom Phaeodactylum tricornutum (Mauzerall and Dubinsky (1993), Biochim. Biophys. Acta 1183, 123-129). Dependence would mean the existence of charge transfer among adjacent units and would be manifested by different saturation curves for the individual flashes of a sequence (different cross-sections), stronger damped oscillations and oxygen formation under the first flash, independently of the length of dark adaptation. We show in the present publication that in the filamentous cyanobacterium Oscillatoria chalybea the O2-evolution pattern which shows an O2-signal under the first flash (despite dark adaptation) can be explained within the heterogeneous Kok-model, assuming a non-standard initial S-state distribution (Bader, Thibault and Schmid (1983), Z. Naturforsch. 38c. 778-792).

Ground‐based search for X rays generated by thunderstorms and lightning

A series of ground‐based experiments have been performed to investigate gamma ray/X ray count rate increases that are associated with thunderstorm and lightning activity. NaI scintillation detectors were configured in a long‐timescale channel to monitor long‐term count rate variations (on timescales of 1–104 s) as a function of time, pressure, temperature, humidity, electric field, rainfall, and general thunderstorm activity and in a short‐timescale channel that was triggered by an electric field change meter to monitor correlations of individual counts (on timescales of 10−7–10−2 s) with particular phases of a lightning flash. Long‐timescale results typically show count rate increases of a few percent to as much as 100% above background levels during thunderstorm activity and are likely due primarily to gamma ray emissions from radon daughter‐ion decay as the daughter ions are precipitated to the ground by rainfall. The production of bremsstrahlung X rays by a thunderstorm runaway electron mechanism cannot be ruled out by this data, but the data indicate that if the mechanism is in operation, the bremsstrahlung flux at the ground is at best intermittent and/or barely discernible above background levels. Short‐timescale results do not show any evidence for the production of X rays by individual lightning flashes. However, these results are inconclusive since only 10 cases of lightning flashes within a 1 km distance were recorded. The results of the overall study are compared to previous studies which claim positive correlations of count rate increases with thunderstorm and lightning activity. They are also discussed in terms of runaway electron acceleration in thunderstorm electric fields and in terms of the runaway air breakdown mechanism for lightning initiation. A review of the physics of and previous studies of X ray emissions from thunderstorms and lightning is presented in the introduction.

Cone ERGs to Flash Trains: The Antagonism of a Later Flash

The human cone electroretinogram (ERG) to flash trains and double flashes at different interflash intervals was studied. A double ganzfeld stimulator was used in which computer controlled flashes were presented independently in the presence of strong rod saturating backgrounds. Corneal ERGs were examined at different frequencies of flash train presentations. Flash trains with individual flashes of high frequency (100 Hz) stimulate a cone ERG to light pulses of long duration by producing a corneal positive off-response ( d-wave) time locked to the cessation of the train. A second flash can reduce and delay the cone b-wave produced by a first flash. This effect is maximal when the second flash occurs 10–12 msec later. There is an antagonistic mechanism in the cone system of the retina which can catch and reduce the cone b-wave produced by an earlier flash. Copyright © 1996 Elsevier Science Ltd.

Laser flash absorption spectroscopy study of flavodoxin reduction by photosystem I in Synechococcus sp. PCC 7002.

The photoreduction of flavodoxin by trimeric photosystem I, both from the cyanobacterium Synechococcus sp. PCC 7002, was investigated by flash absorption spectroscopy. After addition of flavodoxin in darkness, single flash experiments show that the transient signals change between individual flashes. This behavior is assigned to a progressive accumulation of flavodoxin semiquinone, which is relatively stable under most experimental conditions. Different conditions were devised in order to study the reduction of the oxidized and semiquinone forms of flavodoxin separately. Both processes were identified by their differential spectra measured between 460 and 630 nm. Detailed kinetic characteristics of flavodoxin reduction were obtained at pH 8.0 in the presence of salts. The kinetics of reduction of oxidized flavodoxin displays a single-exponential component. The rate of this component increases with the flavodoxin concentration up to an asymptotic value of about 600 s-1. The semiquinone form of flavodoxin being protonated, this rate corresponds to a rate-limiting reaction which could be either an electron transfer reaction or a protonation reaction. In contrast, the reduction of flavodoxin semiquinone is biphasic. A fast first-order phase with t 1/2 approximately 10 microseconds is interpreted as an electron transfer process within a preformed complex. A dissociation constant of 2.64 microM is calculated for this complex by assuming a simple binding equilibrium between photosystem I and flavodoxin semiquinone. The slower phase observed for semiquinone reduction is concentration dependent, and a second-order rate constant of 1.7 x 10(8) M-1 s-1 is calculated. For both one-electron reduction steps, different optimal salt concentrations are observed indicating slightly different interactions between photosystem I and flavodoxin in its oxidized and semiquinone states.

Interactions among the Photosystem II oxygen-forming complexes: A novel model for damping of O 2 oscillations

It is commonly assumed that the oxygen-evolving centers (OEC's) of PS II operate independently, meaning that there is no transfer of charge among adjacent units, and therefore, that in order to evolve an oxygen molecule each such OEC has to accumulate four charges, as it progresses through the ‘S n ’ states. This assumption predicts that when a dark-adapted photosynthetic system is exposed to a series of single turnover flashes, the oxygen yield following the third flash will be the product of the fractions of the population of OEC's hit by each of these flashes, and of their initial distribution of S-states. Indeed, measurements with the chlorophyte Chlorella vulgaris and the diatom Phaeodactylum tricornutum show that their oxygen centers are independent, theformer as expected from previous measurements, and predicted by standard theory. However, by this criterion, the centers of the cyanobacterium Synechococcus leopoliensis are not independent. Moreover, in S. leopoliensis the apparent cross-sections derived from the saturation curves for the individual flashes differ from each other, whereas in the former two species, they are constant. Another criterion of independence is the extent of coherency in the Joliot-Kok (period four) oscillations of the flash yield of oxygen. The more independent the OEC's are, the more these oscillations will persist. If the charge flows through a common pool, as in hydrogen formation, the (period two) oscillations are rapidly damped out. By this criterion S. leopoliensis again differs from the classic Chlorella pattern, since the oscillations in this cyanobacterium are rapidly damped. S. leopoliensis differs from Chlorella in additional parameters: oxygen is maximal on the fourth, not the third, flash and oxygen is formed on the very first flash irrespective of the length of dark adaptation. We propose a new model integrating and quantitatively explaining these observations, by allowing 30% of the oxygen-forming centers in S. leopoliensis to exchange charge. A different dark-state distribution of the S-states, maximal at S 0, is also required. The possibility of charge exchange in other systems is discussed.

A reexamination of the peak current calibration of the National Lightning Detection Network

The peak current calibration of the National Lightning Detection Network (NLDN) recently reported by Orville (1991) has been reexamined with a roughly threefold larger data set of 57 directly measured stroke peak currents, Ipeak (kiloamperes), and their corresponding NLDN mean normalized magnetic signal strengths, (LLP units). These 57 lightning strokes originated in 36 triggered lightning flashes initiated at the Kennedy Space Center (KSC), Florida, during the research campaigns of 1985–1991. Identification of corresponding Ipeak and measurements was verified through accurate coincidence in absolute time of the two independent data sets. The data (with one point excluded as an outlier) is apparently linearly related with a correlation coefficient of 0.881, consistent with that predicted by application of the transmission line model of the lightning return stroke. The regression equation for prediction of Ipeak from NLDN measurements is where the slope is expressed in kiloampere/(LLP units). Examination of the overall data set for the possible influence of two different models of signal strength attenuation with distance, D, (power law, Dβ, and exponential, [expαDD]−1) indicates negligible sensitivity to the proposed variations; other larger error sources likely mask the true attenuation effect. Twelve flashes were detected with four or more direction finders; a power law fit to the direction finder signal strength variation with distance of these individual flashes yields a mean β value of −1.09. Examination of the overall data set for the possible effect of a nonlinear relation between the source stroke peak current and return stroke propagation speed indicates no obvious influence. The 95% confidence bounds for peak current prediction in the mean suggest a percent uncertainty of 10–15% for peak currents between 15 and 60 kA. Similar accuracy is expected for peak currents greater than 60 kA provided care is taken to minimize possible nonlinear amplification effects hi the NLDN data. Below 15 kA, the percent uncertainty rapidly increases suggesting that the inferred distribution of peak current values less than this limit may be quite unreliable.

CIRCADIAN REGULATION OF BIOLUMINESCENCE IN THE DINOFLAGELLATE PYROCYSTIS LUNULA1

ABSTRACTIn the unicellular algae Pyrocystis lunula Schütt and Gonyaulax polyedra Stein, bioluminescence and its circadian regulation are similar in several respects, but there are also several important differences. As in G. polyedra, P. lunula emits light both as bright flashes and as a low intensity glow. At 20° C, the individual flashes are considerably brighter than in G. polyedra, and their durations are typically less than 500 ms. Both species show a circadian rhythm in the frequency of spontaneous flashes, which peaks in the night‐phase under light–dark cycles and continues in both continuous light and dark. However, compared to G. polyedra, the circadian system in P. lunula is more sensitive to light: 10 min exposures (500 μmol · m–2· s–1 white light) can shift the phase of the rhythm by more than 8 h, and rhythmicity is completely suppressed at an irradiance above 20 μmol · m–2· s–1, where the G. polyedra rhythym persists for weeks. Like G. polyedra, period length increases with increasing irradiance of continuous red light but decreases with increasing intensity of continuous blue light. The glow in P. lunula differs markedly from that in G. polyedra in that it occurs at about the same intensity at all times during the circadian cycle; thus, it is not under circadian control but may fluctuate 5–10‐fold in intensity within a time frame of seconds. This suggests that the glow may differ in its physiological basis in the two organisms. The results also indicate that the circadian regulation of luciferase activity differs in the two species. In G. polyedra, the organelle responsible for bioluminescence and luciferase is lost and then reformed on a daily basis; in P. lunula, the luciferase is conserved and localized elsewhere during the nonbioluminescent phase of the cycle.

Sublinear summation of responses in locust photoreceptors

The response of a locust, Locusta migratoria, photoreceptor to a simultaneous pair of dim flashes is smaller than the sum of the responses to the individual component flashes, even when the photon absorption sites are separated by a distance of 120 μm, which should prevent them from interacting biochemically. A similar depression is observed when a flash is paired with a depolarizing current instead of a second flash, irrespecive of whether the flash response precedes or follows the current response. These results indicate that the sublinear summation is caused by the activation of a voltage-activated shunting conductance. This conductance is not blocked by low intracellular concentrations of tetraethylammonium chloride, and is therefore different from the conductance which causes the decrease of the receptor's step response from transient to steady-state.

Physiological roles of Na+/Ca2+ exchange in Limulus ventral photoreceptors.

In previous work we have presented evidence for electrogenic Na+/Ca2+ exchange in Limulus ventral photoreceptors (1989. J. Gen. Physiol. 93:473-492). This article assesses the contributions to photoreceptor physiology from Na+/Ca2+ exchange. Four separate physiological processes were considered: maintenance of resting sensitivity, light-induced excitation, light adaptation, and dark adaptation. (a) Resting sensitivity: reduction of [Na+]o caused a [Ca2+]o-dependent reduction in light sensitivity and a speeding of the time courses of the responses to individual test flashes; this effect was dependent on the final value to which [Na+]o was reduced. The desensitization caused by Na+ reduction was dependent on the initial sensitivity of the photoreceptor; in fully dark-adapted conditions no desensitization was observed; in light-adapted conditions, extensive desensitization was observed. (b) Excitation: Na+ reduction in fully dark-adapted conditions caused a Ca2+o-dependent depolarizing phase in the receptor potential that persisted beyond the stimulus duration and was evoked by a bright adapting flash. (c) Light adaptation: the degree of desensitization induced by a bright adapting flash was Na+o dependent, being larger with lower [Na+]o. Na+ reduction enhanced light adaptation only at intensities brighter than 4 x 10(-6) W/cm2. In addition to being Na+o dependent, light adaptation was Ca2+o dependent, being greater at higher [Ca2+]o. (d) Dark adaptation: the recovery of light sensitivity after adapting illumination was Na+o dependent. Dark adaptation after bright illumination in voltage-clamped and in unclamped conditions was faster in normal-Na+ saline than in reduced Na+ saline. The final sensitivity to which photoreceptors recovered was lower in reduced-Na+ saline when bright adapting illumination was used. The results suggest the involvement of Na+/Ca2+ exchange in each of these physiological processes. Na+/Ca2+ exchange may contribute to these processes by counteracting normal elevations in [Ca2+]i.

Simultaneous Disturbance of Conjugate Ionospheric Regions in Association With Individual Lightning Flashes

Characteristic whistler‐associated amplitude perturbations of subionospheric VLF or LF signals (“Trimpi events”) observed within one second of each other at Palmer Station, Antarctica and at Arecibo, Puerto Rico suggest that ionospheric regions in both northern and southern hemispheres are disturbed together in association with individual lightning flashes. During a one hour period on March 21, 1989, the onsets of 44 out of 47 perturbations measured on a 21.4 kHz signal from Maryland to Arecibo occurred within l s of perturbation onsets measured on a 23.4 kHz signal from Hawaii to Palmer Station. Similar activity occurred before and after this period, and on the preceding and following days. The observations are consistent with the disturbance of geomagnetically conjugate ionospheric regions by multiple bounces between hemispheres of bursts of radiation belt electrons, scattered in pitch angle by whistlers in the magnetosphere. Analysis of patterns of perturbations with corresponding whistler and lightning information from this period suggests that there were at least two distinct ionospheric disturbances in each hemisphere.

Recovery and stimulation of copepod bioluminescence

The depletion of bioluminescence that occurs during net collection and handling, and its subsequent recovery, was investigated in three species of oceanic calanoid copepods, Pleuromamma xiphias (Giesbrecht), Lucicutia flavicornis (Claus), and Gaussia princeps (T. Scott). Only 14–38% of total bioluminescence was present l h after collection. Recovery of light emission occurred at an exponential rate which did not vary with species. Full recovery of bioluminescence occurred within 1 day, and was due to increases in both the quantum emission of individual flashes and the number of flashes contributing to the response. Total bioluminescence was related to species size, as was the time to full recovery. Once fully recovered, P. xiphias produced three types of flashes in response to mechanical stimulation. These flash types differed in response kinetics and quantum emission. The rate of mechanical stimulation affected the rate at which flashes were produced and not the total amount of bioluminescence. Therefore, stimulus strength and duration will influence the nature of the bioluminescent response.

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.

Responses of cat visual cortical cells to continuously and stroboscopically illuminated moving light slits compared

We have compared responses of cat visual cortical cells of area 17 to continuously illuminated moving slits and to moving slits illuminated stroboscopically at different rates (70-2 Hz) using quantitative multihistogram techniques. At strobe rates over 30 Hz response characteristics of cortical cells are almost identical under both conditions, except for a lower response level under stroboscopic illumination. As strobe rates decrease below 30 Hz. direction selectivity and velocity tuning are severely impaired and some cells start responding to the individual strobe flashes rather than to the motion of the slit.

Daylight Spectra of Individual Lightning Flashes in the 370–690 nm Region

An optical multichannel analyzer slit spectrometer coupled to a minicomputer was used to record lightning spectra. This is the first successful application of a slit spectrometer to the study of individual lightning flashes and it was accomplished in the daytime. Over 300 spectra were obtained in 1978 and 1979 and are correlated with other experiments in the Thunderstorm Research International Program (TRIP). The spectra duplicate previously published nighttime data but reveal for the first time the relative intensity of H-alpha (656.3 nm) and H-beta (486.1 nm) emissions above their daytime absorption features. These are the characteristic Fraunhofer C and F lines in the solar spectrum. This result suggests that the observation of lightning from space may be accomplished by monitoring the hydrogen emissions from lightning which occur on earth, or on other planets with hydrogen in their atmospheres, such as Jupiter and Venus where lightning recently has been reported.

New Spectrographic Observations of Flashes in Burning Iron Particles

New spectrographic observations have been made of the flashes of light appearing in small burning iron particles produced in a grinding wheel. In a dispersion of about 80 Ångström per mm slitless spectra of individual flashes show a great number of Fe I lines as well as molecular bands due to FeO, C2, CN and N2. The region observed is between 5160 and 5870 Å. These observations confirm earlier observations by the writer, that discharge phenomena appear in connection with the splitting of a particle in two or more parts. That is to say, the light emission of a flash is due to a discharge spectrum superimposed on a continuous spectrum due to thermal emission.Possible astrophysical applications are briefly discussed.