AE31A-0252
Modeling the Diffuse Cloud-Top Optical Emissions From Ground and Cloud Flashes
A number of studies have indicated that the diffuse cloud-top optical emissions from intra-cloud (IC) lightning are brighter than that from normal negative cloud-to-ground (CG) lightning, and hence would be easier to detect from a space-based sensor. The primary reason provided to substantiate this claim has been that the IC is at a higher altitude within the cloud and therefore is less obscured by the cloud multiple scattering medium. CGs at lower altitudes embedded deep within the cloud are more obscured, so CG detection is thought to be more difficult. However, other authors claim that because the CG source current (and hence luminosity) is typically substantially larger than IC currents, the greater CG source luminosity is large enough to overcome the effects of multiple scattering. These investigators suggest that the diffuse cloud top emissions from CGs are brighter than from ICs, and hence are easier to detect from space. Still other investigators claim that the detection efficiency of CGs and ICs is about the same because modern detector sensitivity is good enough to "see" either flash type no matter which produces a brighter cloud top emission. To better assess which of these opinions should be accepted, we introduce an extension of a Boltzmann lightning radiative transfer model previously developed. It considers characteristics of the cloud (geometry, dimensions, scattering properties) and specific lightning channel properties (length, geometry, location, current, optical wave front propagation speed/direction). As such, it represents the most detailed modeling effort to date. At least in the few cases studied thus far, it was found that IC flashes appear brighter at cloud top than the lower altitude negative ground flashes, but additional model runs are to be examined before finalizing our general conclusions.
AE31A-0253
Estimations of Electrical Conductivity above Thunderstorms
Electrical conductivity of the atmosphere is an important parameter in the Global Electric Circuit (GEC), but it is somewhat difficult to measure above thunderstorms. However, most lightning flashes produce transient increases in the electric field magnitude (E) above their parent thundercloud, and the decay of each transient E increase can be used to estimate the above-storm conductivity. The E transients can be measured with sensors carried above the thundercloud by balloons. In this presentation we estimate the conductivity above three small thunderstorms by combining balloon E data, Lightning Mapping Array data, and radar data. Conductivity measurements were made for eight intra-cloud (IC) flashes at times when the balloons were over thunderstorms in the altitude range of 9 to 13 km msl, or from just above cloud top to 2.4 km above cloud top. Our analyses show that the conductivity profile that best fits our data is [7.0 × 10-14] exp (z/8) S/m, where z is altitude in km above mean sea level. This result is in good agreement with above-storm conductivity measurements of Holzworth et al. [1985].
AE31A-0254
Lightning Mapping Observations of the 2006 Eruption of Augustine Volcano, Alaska
In January of 2006 Mt. Augustine erupted explosively producing ash plumes that often exceeded 9 km in altitude. A small Lightning Mapping Array was deployed east of Mt. Augustine in Alaska and was in operation for the eruption on January 28, 2006. Our observations show a lightning sequence in the volcanic plume (called the plume phase), which began approximately ten minutes following the onset of the eruption, and extended to distances up to 22 km from Augustine's vent. Though only two stations were deployed for this eruption, one station functioned as a sea-surface interferometer. This has enabled us to determine some altitudes of the VHF sources. Using interferometry techniques combined with time-of-arrival analysis, the lightning sequence on January 28, 2006 has been analyzed. We will present details of the temporal evolution of the lightning activity that developed in the volcanic plume as it drifted southward. In addition, we will compare and contrast our observations of volcanic plume lightning with thunderstorm lightning.
AE31A-0255
Improving techniques for satellite-based constraints on the lightning parameterization in a global chemical transport model
The GEOS-Chem 3D global chemical transport model is used to demonstrate the sensitivity of the global ozone budget to spatial and temporal variability in the parameterization of lightning emissions of reactive nitrogen oxides (NOx). Global atmospheric chemistry models must parameterize lightning formation as part of their convective simulations and on the basis of large-scale meteorological variables, attenuating sub- grid processes that drive lightning variability. The High Resolution Monthly Climatology (HRMC) combined product of the Optical Transient Detector (OTD) and the Lightning Imaging Sensor (LIS) covering the period 1995-2005 available from the NASA Global Hydrology and Climate Center (GHCC), as well as the individual Science Data orbits of the LIS (1998-present) are used here as top-down constraints on the lightning parameterization in GEOS-Chem, driven by assimilated meteorological products of the NASA Global Modeling and Assimilation Office (GMAO). Different techniques are explored for spatially redistributing the lightning density via local scaling factors determined by comparing the unscaled parameterized and observed LIS/OTD climatology product for the 11-year observation window. A series of simulations compares the impact of this redistribution performed at different scales: at native model resolution ("local"), increasingly larger-scale regions as identified by a hierarchal clustering algorithm ("regional"), and no redistribution at all. The local technique allows for sharper spatial variability and stronger correlation to the climatology, but regional methods stay truer to the physically-based parameterization and model physics with scaling factors closer to unity, enable more robust statistics, while yielding similar impacts on the ozone budget. The regional methods also enable additional constraint of temporal variability within GEOS-Chem by permitting much more robust sample sizes of the LIS Science Data orbits for determination of interannual monthly scaling factors for each tropical and subtropical region. The impact of constraining temporal variability in the model is studied over simulations over the first 9-years with available LIS data. Validation is performed against various in situ and satellite observations of upper tropospheric photochemical species, in particular, the long-term ozonesonde observations available through the World Ozone and Ultraviolet Radiation Data Centre (WOUDC). The ability of GEOS-Chem to capture large-scale features of the interannual ozone budget in space and time (e.g., the South Atlantic maximum) is explored.
AE31A-0256
Investigation of lightning flash morphologies along the entire supercell life cycle using a numerical 3D cloud resolving model(CRM).
A stochastic lightning flash scheme has been implemented in line in a meso-sca le CRM. It is fully parallelized and vectorized. In this model, a lightning flash is schematized as two single conducting channels (single tracks) propagating in opposite directions from the lightning ignition point. Branch patterns propagate from the single channels. On the base of scale similarities between discharges in dielectrics at centimeter scales and lightning flashes, the stochastic scheme has been designed to compute branch trajec tories. Physical considerations and branch fractal dimensions compel branch trajectories. The charge neutralization operates along the single tracks and branches to threshold the cloud electrical charge. First, an assessment of the scheme will be presented in simple 2D configurations. Second, we will describe comprehensive 3D-thundercloud life-cycle simulations including cloud electrification and lightning discharges. Lightning flash patterns are analyzed through statistics of their effective fractal dimension. It is shown that paradoxically, lightning flashes with quasi-plane branch propagation (fractal dimension close to 2) lead to more steady electrical behavior than those completely filling volumes (fractal dimension close to 3).
AE31A-0257
The effect of spatial resolution on numerical simulation of non-inductive electrical charge separation in thunderstorms
Our goal is to quantify the effects of limited spatial resolution on numerical modeling of electrical charge separation in thunderstorms. Within a thunderstorm there are relatively large regions that are dynamically quiet where microphysical properties are relatively homogeneous. There are relatively narrow regions in which there are sharper gradients in microphysical properties. The edges of well-developed updrafts in particular are often characterized by very sharp gradients in liquid water concentration, hydrometeor concentrations, and temperatures, all of which are important factors in non-inductive charge separation. Numerical storm electrification modeling indicates that these regions on the edge of updrafts are also characterized by relatively higher values of electrical charge separation via the non-inductive charging process that are very important in the overall electrification of the storm. However, the gradients of microphysical properties observed on the edges of updrafts observed in actual thunderstorms usually cannot be realistically resolved in numerical models that typically have 500 m or even 1000 m horizontal grid spacing. The relatively low model resolution leads to a smoothing of the gradients and possible inaccuracies in results of the charge separation algorithm. We calculate charge separation rates based on in situ microphysical measurements obtained along the trajectory of an instrumented aircraft passing through a thunderstorm core using algorithms from the South Dakota School of Mines storm electrification model. The aircraft observations intrinsically have 100 m resolution. These observations are degraded to 500 m and 1000 m resolution and the calculations are repeated to demonstrate the impact of lower spatial resolution on calculated charge separation rates.
AE31A-0258
Predicting lightning density in Mediterranean storms based on the WRF model dynamic and microphysical fields
Explicit simulations of cloud-scale processes for operational forecasting are now performed with ~3 km grid scale resolution, enabling model output fields to include vertical velocity at the scale of large convective clouds, as well as cloud water, cloud ice, snow, and graupel concentrations. We introduce the Lightning Power Index (LPI) which is a measure of the potential for charge generation and separation that leads to lightning flashes in convective thunderstorms. The LPI is calculated within the charge separation region of clouds, where the non-inductive mechanism by collisions of ice and graupel particles in the presence of super-cooled water is most effective. As shown in several case studies in the Mediterranean region using the Weather Research and Forecasting Model (i.e., WRF) with explicit microphysics, the LPI is highly correlated with observed lightning. The superiority of the LPI against conventional thermodynamic indices for lightning prediction such as the KI and CPTP was clearly demonstrated for these case studies. It is suggested that the LPI may be a useful parameter for predicting lightning as well as a tool for improving weather forecasting of convective storms and flash floods.
AE31A-0259
High Electric Fields at the Kodiak Launch Complex
The Alaska Aerospace Development Corporation (AADC) owns and operates the Kodiak Launch Complex (KLC) on Kodiak Island, Alaska. Orbital and sub-orbital vehicles are launched from KLC. Several weather criteria are evaluated during ground operations and launch activities at KLC to assure personnel and vehicle safety. Certain lightning safety criteria define electric field thresholds measured by ground-based field mills that cannot be exceeded in order to ensure that launch vehicles will not trigger lightning during flight, and protect personnel and equipment from natural lightning. Range personnel report the occurrence of unusually high electric field values exceeding the defined thresholds resulting in work schedule and launch delays. Although there is a likely threat for triggered lightning when electric field values are elevated, natural lightning rarely occurs in the Kodiak Island area. To address this issue, AADC tasked ENSCO, Inc to use the available meteorological data from KLC and determine the possibility of new ways to evaluate the field mill thresholds, for both triggered and natural lightning, while maintaining safety using data archived at KLC during the events. The data used in this work were archived during launch preparation operations in May 2007 and included surface observations, upper-air soundings, and radar. Several extreme electric field values were recorded during May 2007, e.g. -13 kV/m on 15 May, -7 kV/m on 22 May, and +5 kV/m on 24 May. There were precipitating clouds in the area during each of the events, but there were no observations of natural lightning. Estimates from soundings taken during the events showed the existence of thick clouds and very low freezing levels. The electric fields tended to become largely negative when precipitation rates increased, and positive when the rates decreased. This indicated that the electric fields were related to charges in precipitating clouds moving across the network. It is clear that a strong electrification process occurred in these clouds, yet the triggering threshold for natural lightning was not reached. The goal of this presentation is to introduce this issue to the scientific community and stimulate interest in learning more about the charging mechanisms in these high-latitude cloud systems. This is not just a topic of scientific interest, but one that has a significant effect on space launch operations at KLC.
AE31A-0260
Does the Altitude of the Charge Source Region Influence Stroke Multiplicity?
Many differences exist between positive and negative cloud-to-ground (CG) lightning flashes, though these differences are not well understood. Observations show that negative CG flashes tend to have multiple return strokes with little continuing current from each stroke, whereas positive CG flashes tend to have only one return stroke with continuing current. Though the reason for this polarity asymmetry in terms of multiple strokes has not been identified, the leading hypothesis is related to the idea that the return stroke channel needs to be maintained by infusion of current from within the cloud. Insufficient infusion of current in the initial return stroke may lead to channel decay, thus resulting in a successive stroke. However, if this infusion of current is sufficient enough to maintain the initial stroke channel, then there may be large continuing current down the initial channel and no subsequent strokes. One possible factor involved in this process is the difference in the altitude of the charge source region of positive CG versus negative CG flashes. If the source region for negative CG flashes is further from ground, then negative CG flashes would require a longer channel to the ground. A longer channel length may require a larger infusion of current to maintain it and thus be more likely to decay and require a subsequent stroke. Our hypothesis is that, regardless of polarity, longer channel lengths lead to multiple strokes, whereas shorter channels are more likely to be single-stroke with continuing current. We will test this hypothesis by using the National Lightning Detection Network (NLDN) and Lightning Mapping Arrays (LMAs) to determine the relationships among polarity, number of strokes, and source altitude. Preliminary results indicate that source altitudes for negative CGs are between 5 and 6 km, whereas source altitudes for positive CGs are between 8 and 9 km. Though these initial results are contrary to our hypothesis, we will analyze a larger, more diverse data set before making any conclusions.
AE31A-0261
Electrical Properties of an Asymmetric Mesoscale Convective System on 4 June 2003
This case study investigates lightning initiation locations and production within an asymmetric mesoscale convective system (MCS) that occurred in central Oklahoma on 4 June 2003. Lightning data from the Oklahoma Lightning Mapping Array and the National Lightning Detection Network, electric field data from six electric field meter soundings and a T-28 aircraft flight, thermodynamic data from the soundings, and microphysical data from the polarimetric WSR-88D KOUN radar in Norman, Oklahoma and from the T-28 aircraft flight are analyzed to investigate connections between portions of the electrical and microphysical properties of this storm. The MCS had a low flash rate but exhibited multiple significant charge layers in the stratiform region. Both up and down soundings showed a negative charge layer near the melting layer. Most of the lightning initiation points were found in the leading convective line.
AE31A-0262
LASA Observations of Lightning in Hurricanes
As first observed by the Los Alamos National Laboratory Sferic Array (LASA) in 2005, hurricanes Katrina and Rita had an unusually large amount of lightning associated with them. Of particular interest is the lightning in the eye wall, indicative of convection, which increased in rate as the storms intensified. LASA measures the VLF/LF vertical electric field change at several stations located throughout Florida and the Great Plains region, and uses time-of-arrival techniques to locate lightning up to several hundreds of kilometers away. Complete waveforms are saved and can be used to determine quantities such as the type and polarity of the discharge, and in some cases the height. Information about the lightning events in the eye wall region may further our understanding of the intensification of hurricanes. In the summer of 2008, the LASA sensors were upgraded, and a new system was deployed in the New Orleans area to further investigate the role of lightning in hurricanes.
AE31A-0263
Delineating Urban-enhanced Lightning Production: An approach using Flash-defined Thunderstorm Tracks.
Lightning hazards are often less spectacular and more isolated than those produced by hurricanes or tornadoes. Consequently, lightning has been under recognized in its potential to generate large economic losses. Recent studies have found that heat generated from large urban areas alter the local distribution of lightning. However, little is known about the characteristics of this lightning and how surface properties and land-use trends influence its damage potential. Evidence suggests, trends in lightning property damage can be attributed to the background thunderstorm regime, a control imposed by the physical environment. Other studies emphasize that these loss trends are caused by an increasing societal sensitivity to thunderstorms through urbanization. This investigation is unique in that there is simultaneous consideration of the physical environment and the societal template as interacting causal agents. The study region, Atlanta, Georgia, USA provides an ideal setting to investigate how these interactions shape lightning hazards. Results suggest that the highly populated suburban counties to the northeast of downtown Atlanta have lightning strike densities approaching those along the lightning active northern Gulf Coast of Florida. This flash density hotspot is collocated with a zone of high-density land use indicative of urban flash augmentation. In addition, a lightning tracking algorithm revealed the nature of individual thunderstorm tracks creating the hotspot. Increases in lightning flash production were noted in individual storms passing over high-density urban land use.
AE31A-0264
Spider-like lightning observation using VHF broadband digital interferometer
Lightning Research Group of Osaka University (LRG-OU) has been developing the VHF broadband digital interferometer since 1995. This is a two- (2D) and three-dimensional (3D) VHF source mapping system for electromagnetic (EM) waves emitted by lightning discharge progression based on a unique technique of the broadband digital interferometry. LRG-OU carried out field observation campaigns with the VHF broadband digital interferometers during monsoon seasons in Darwin, Australia. Through these campaigns a lot of lightning channels were visualized. The bi-directional leader progression, possible charge distribution related to the leader initiation, and the speed of the leader propagation are studied by the 3D imaging. At 0943:13 UT on 13 December, 2006, a spider-like cloud-to-cloud (CC) flash is recorded. In this flash, 4 groups of leaders are clearly visualized simultaneously. All leaders initiate from similar location, but develop to 4 different directions. One of these goes up to over 9km height, while the others progress horizontally between 2 and 5 km high. According to the weather radar observations by BOM, the bright band is noticeable at about 5 km high. It means the lower leaders progress under "melting snow" layer and positive charges exist in this region. It is considered that the lower leaders develop as long as 8 km horizontally neutralizing freckled positive charge. The leaders resembling dart leaders that propagate through the exact same channel as previous leader are also seen in this flash. The precedent leader proceeds with a speed of about 104 m/s, and then subsequent leaders proceed at a speed of about 106 m/s. In the presentation, we would like to discuss about the details of this spider-like CC flash.
AE31A-0265 [WITHDRAWN]
Departures from Sinusoidal Variation in the Occurrence of Lightning in Equatorial Africa
Lightning in many African countries has a well defined pattern of occurrence which is well described by a sinusoidal curve that peaks close to the summer solstice.(Collier et al. 2006). Interesting departures from this pattern occur in countries bordering the Gulf of Guinea and these can be explained by the annual migration of the inter-tropical convergence which greatly influences weather in that region. Detailed curves for the occurrence of lightning are given for all African countries derived from the LIS instrument on the TRMM spacecraft for seven years of observation.
AE31A-0266
Three Dimensional Current Generator Structure of a Mountain Thunderstorm: Analysis of Some Interesting Flashes
Recently, wide band measurements of the electric field near a lightning flash have been obtained by a balloon-borne electric field sonde or Esonde. The data from the Esonde can be combined with simultaneous Lightning Mapping Array (LMA) measurements of VHF pulses emitted dur- ing lightning breakdown processes to estimate the charge transport associ- ated with lightning. In this paper, we further enhance the techniques we have developed to process Esonde data by taking better account of instrument ro- tation, and by computing the local horizontal electric field, not just the lightning induced electric field change. Using these techniques, we analyze light- ning charge transport for a thunderstorm which occurred on August 18, 2004, near Langmuir Laboratory, New Mexico. The analysis yields the three dimensional current generator structure of the thunderstorm. Some of the flashes occured during the storm have interesting structures. Detailed analysis of those flashes are presented.
AE31A-0267
Estimating Thunderstorm Generator Currents
A technique has been developed to estimate from observations the thunderstorm generator current, an important parameter for the global electric circuit as well as a measure of the strength of in-cloud charging mechanisms. For one cell the method indicates that during a three-minute time interval the in-cloud charge generation produced an average current of about 0.4 A. Similar analysis in another developing thunderstorm cell with a short lifespan indicates that the early generator current was as large as 0.14 A, but it decreased by a factor of about three as the cell began to dissipate and merge with another cell less than 7 min later. This presentation will describe the method and results, and then compare the estimated generator currents to other estimates of the various currents flowing in the thunderstorm environment.
AE31A-0268
Preliminary results of a laboratory study of positive streamer discharges from vapor-grown ice crystals subjected to electric fields
The initiation of lightning remains a subject of ongoing scientific debate, due in large part to a lack of sufficiently detailed observations. Recently, theoretical descriptions of lightning initiation have focused on the problem of the relatively weak thundercloud electric field by proposing physical processes, primarily those associated with runaway breakdown, whereby this weak field might be significantly boosted. While hypothesis that runaway breakdown is necessary for lightning initiation is compelling, it cannot be considered complete as the transition to lightning leader is not a trivial step. Such a transition must involve processes capable of converting the diffuse electric field energy into a hot leader channel. Such processes likely include the streamer discharge as an element, with such streamers possibly originating as corona discharges on nearby hydrometeors. Of interest to this study is the positive streamer discharge on an ice hydrometeor. We present preliminary results of a laboratory investigation of positive streamer discharges on vapor-grown ice crystals that were subjected to electric fields while growing in a water vapor diffusion chamber. The resulting data shows the electric fields required for generating single and multiple positive streamer discharges as a function of ice crystal habit, size and temperature and ambient air pressure. These results provide useful information for investigating the role of hydrometeor-generated streamer discharges in the lightning initiation event.
AE31A-0269
High-Speed Video, Mapping and Broadband Electric Field Recordings of Lightning
During the summer of 2008 New Mexico Tech's Lightning Mapping Array (LMA) was reconfigured from a compact to a more widely-spaced network around the Langmuir Laboratory for Atmospheric Research. This change increases its three-dimensional location accuracy further away from the center of the array, as well as reducing false correlations caused by local corona and TV-broadcast interference. The LMA operated in a high time-resolution mode which located RF sources from lightning as often as once every 10 microseconds. We also operated a Vision Research Phantom v7.3 high-speed video camera to make recordings of lightning leaders around the mountaintop laboratory, typically at a rate of 6400 frames per second. These recordings are time-tagged by GPS allowing us to accurately compare individual frames with LMA data. In addition to lightning mapping data and video recordings we acquired broadband electric field waveforms from lightning, up to 100 MHz in bandwidth. These instruments are a comprehensive tool for studying lightning leader processes in great detail. In particular, we focus on continuing our studies into the leader behavior of bolt-from-the-blue lightning, where the leader exhibits a transition from impulsive to more continuous RF radiation as it exits the cloud and propagates to ground.
AE31A-0270
Recent findings on lightning characteristics using high-speed video recordings in Brazil and USA
From analyses of digital high-speed video records of more than a thousand negative cloud-to-ground (CG)
lightning flashes and tens of positive CG flashes produced by warm-season thunderstorms in southeastern
Brazil, Arizona, and South Dakota, various lightning properties have been determined. This work will show
recent findings on the following: percentage single-stroke flashes, average number of strokes per flash,
percentage of flashes with multiple ground terminations, average number of strike points per CG flash, time
intervals between strokes, correlation between the number of subsequent strokes in a flash and the minimum
flash duration, relation between estimated peak current and following continuing current, percentage of
flashes containing continuing current, waveshapes of continuing current, and properties of M-components.
We will also present some average leader velocities and will show high-speed video recordings of recoil
leaders during the propagation of positive leaders to ground.
http://www.inpe.br/webelat/homepage/
AE31A-0271
The Fair-weather Electric Field Near the Bird's Nest During the Beijing 2008 Olympic Games
Under the action of a constant current density from the global electrical circuit, the fair weather electric field will vary inversely with the electrical conductivity of the air. The reduction of small ion concentration in polluted conditions is expected to reduce the conductivity and enhance the electric field. The traffic control measures and the reduced power plant emissions aimed at cleaner air during the 2008 Beijing Olympics provide a unique opportunity for investigating this scientific issue. The Earth's electric field has been continuously monitored with an electric field meter near the Bird's Nest, The National Stadium, since May 2008, about three months before the Beijing 2008 Olympic Games. The electric field meter is located about 1.5 km southwest from the Bird's Nest. The diurnal variation of the fair-weather electric field is studied during the entire observation period. The fair-weather electric field during the Olympics Games from 8 to 24, August, when clean air was consistently observed, was compared with that before the pollution control measures became effective. A different diurnal variation and intensity was found during these two scenarios. These preliminary results are significant in understanding the effect of aerosols on fair-weather atmospheric electricity.
AE31A-0272
Infrasonic Observations of Thunderstorms at High Latitudes: Time Scales
The present work summarizes some results of infrasonic observations of thunderstorms recorded in the Northern Scandinavia by the Swedish-Finnish Infrasound Network (SIN). A lightning in the atmosphere is a source of cylindrical shock waves. When the distance from the source increases, more and more energy is transferred into the low-frequency range through the same mechanism as for shock waves from supersonic aircraft. Frequently, semi-regular sequences of lightning with similar orientation and nearly constant repetition frequency are observed. For that reason the spectrum of time delays between individual strokes is studied. It has been found that the apparent random occurrence of strokes seems be a result of superposition of several processes with slowly varying time scales.
AE31A-0273
Infrasound Observations from Lightning
To provide additional insight into the nature of lightning, we have investigated its infrasound manifestations. An array of three stations in a triangular configuration, with three sensors each, was deployed during the Summer of 2008 (July 24 to July 28) in the Magdalena mountains of New Mexico, to monitor infrasound (below 20 Hz) sources due to lightning. Hyperbolic formulations of time of arrival (TOA) measurements and interferometric techniques were used to locate lightning sources occurring over and outside the network. A comparative analysis of simultaneous Lightning Mapping Array (LMA) data and infrasound measurements operating in the same area was made. The LMA locates the sources of impulsive RF radiation produced by lightning flashes in three spatial dimensions and time, operating in the 60 - 66 MHz television band. The comparison showed strong evidence that lightning does produce infrasound. This work is a continuation of the study of the frequency spectrum of thunder conducted by Holmes et al., who reported measurements of infrasound frequencies. The integration of infrasound measurements with RF source localization by the LMA shows great potential for improved understanding of lightning processes.
AE31A-0274
A Versatile Software Program for Sampling Sferics and More
In 2004, a data acquisition program was written to sample and store
sferic waveforms for the upgraded Los Alamos Sferic Array (LASA). The
program acquired data using the 20MHz PCI-DAS4020/12 Measurement
Computing (MC) board on the stable Linux operating system. The
capabilities of this original program have been described elsewhere
[Stanley et al., 2004; Shao et al., 2006]. Starting in 2006, this
program was modified and enhanced to support data acquisition for a
new Charge Moment Change Network (CMCN) which detects and quantifies
impulsive charge moment changes of potential sprite-producing
lightning discharges in near real-time. Some of the more notable
modifications included the addition of low-pass filtered continuous
data output capabilities as well as support for National Instruments
(NI) boards. The continuous data output was particularly well suited
for the unambiguous detection of sferics with slow tails which are
often found around the time of sprites and especially sprite halos.
The program also utilizes a shared memory architecture which gives it
even more versatility in real-time processing as well as enables other
modes of data acquisition. In 2008, the program was updated to
utilize the Linux Comedi drivers in place of the previous MC and NI
drivers. With this modification, the program now supports an even
wider variety of data acquisition boards and also runs on the latest
Linux distributions.
http://www.sferic.info/
AE31A-0275
Los Alamos VHF-VLF Dual Band Lightning Mapping Array
In the summer of 2008, we deployed a 6-station, dual-band lightning mapping array on the shore south of New Orleans, in support of Los Alamos National Laboratory's hurricane intensification study. The new sensor consists of a broadband (10 kHz-80 MHz) antenna, a VHF (60/5 MHz) logarithmic power detector, and a VLF/LF (10 – 500 kHz) waveform detector. The VHF channel is sensitive to VHF power down to -70 dBm, and can be programmed to detect a peak at any chosen time window. The current setup allows a detection of a maximum peak within each 100 microseconds, similar to New Mexico Tech's LMA system. The VHF channel is also capable of continuously recording VHF power waveform at a rate of 1 Mega-sample per second for detailed breakdown process study. The VLF/LF channel is the same as the earlier Los Alamos Sferic Array (LASA) sensors that records the raw field change waveform once triggered. The simultaneous dual band observations will provide unprecedented physics for lightning discharge processes. The VHF band will provide us detailed 3-d channel structure that depicts the progress of small-scale breakdown processes, while the VLF/LF band provide the large-scale current transportation associated with each of the processes. The combination of the two measurements will provide us the charge amount neutralized by each process, a preferred parameter for our hurricane intensification simulation which fuses the storm's electrification process into the convective hydrodynamic process. In this report, we will present the initial performance and the preliminary results of the new dual-band lightning array.
AE31A-0276
On the Multi-Station Schumann Resonance Monitoring of Worldwide Lightning Activity
Three reasons make the electromagnetic radiation in the Schumann resonance (SR) frequency range (5 to 50 Hz) an informative indicator of lightning activity on a global scale: 1) the predominant role of the activity in generating SR fields; 2) an extremely low, below 1 dB per Mm, propagational attenuation; and a beneficial consequence: 3) the occurrence of resonance phenomena in both electric and magnetic spectra as a result of interference between the direct and around-the-globe waves, with an accurate depiction in a theoretical model. The unique dependence of the resonance patterns on the mutual positions of source and observer has been widely exploited for locating individual parent lightning discharges from their SR signatures (transient signals). A similar, but more complicated, relationship between source properties and observed resonance characteristics is present in the case of the 'background' SR signal representing an integration of electromagnetic contributions from thousands of globally distributed lightning flashes. The reasonable agreement between observations and theoretical simulations achieved in typical forward calculations (Mushtak and Williams, 2007) suggests the possibility for an automated procedure for monitoring the global spatial-temporal dynamics of lightning activity from background SR observations. The proposed iterative procedure is based on the estimation of model parameters via a sensitivity matrix, the elements of which are theoretically computed derivatives of resonance characteristics with respect to the model parameters (Nelson, 1967). In a preliminary study, a simple 15-parameter model analogous to that exploited by Mushtak and Williams (2007) - three major "chimneys" each of which is characterized by its intensity (in absolute units of C2 km2/s), the geographical position of its center as well as its latitudinal and longitudinal dimensions – has been used to estimate the various elements of the sensitivity matrix, for choosing an accurate propagational model, and for planning required preconditions for a multi-station SR network. Since a "chimney" is maximally active during the local afternoon hours, it means that within the most contributive period the "chimney" is located close to, or crossed by, the day/night boundary of the Earth- ionosphere waveguide. For this reason, the spherically symmetrical model traditionally used in SR locating procedures cannot provide the required accuracy. Instead, the two-dimensional telegraph equation has been exploited (Kirillov, 2002; Mushtak and Williams, 2007), developed from Madden and Thompson's (1965) transmission line concept specifically for treating the waveguide's asymmetries. The proposed procedure is tested preliminarily on single-station (Rhode Island, USA) observations represented by Lorentzian-approximated spectral resonance characteristics of the background signal (modal intensities, frequencies, and quality factors). It is shown that a reasonable outnumber factor (the ratio of the number of measured characteristics to the number of parameters to be estimated) of 2 or more can be effectively achieved – even in the single-station configuration - by considering the Lorentzian characteristics for the first three Schumann resonance modes. The effect of the inclusion of additional stations in the network is tested in simulations. The advantages and limitations of the suggested SR methodology in comparison with other monitoring techniques (satellite observations, networks for locating transient events, global VLF networks) are also discussed.
AE31A-0277
Scientific Data Stewardship in the 21'st Century
The Ionosonde Program at the National Geophysical Data Center (NGDC) serves as a case study for how to approach data stewardship in the 21'st century. As the number and sophistication of scientific instruments increase, along with the volumes and complexity of data that need to be preserved for future generations, the old approach of simply storing data in a library, physical or electronic, is no longer sufficient to ensure the long term preservation of our important environmental data. To ensure the data can be accessed, understood, and used by future generations, the data stewards must be familiar with the observation process before the data reach the archive and the scientific applications to which the data may be called to serve. This familiarity is best obtained by active participation. In the NGDC Ionosonde Program team, we strive to have activity and expertise in ionosonde field operations and scientific data analysis in addition to our core mission of preservation and distribution of data and metadata. We believe this approach produces superior data quality, proper documentation and evaluation tools for data customers as part of the archive process. We are presenting the Ionosonde Program as an example of modern scientific data stewardship.