The relationship of storm severity to directionally resolved radio emissions

NASA Technical Reports Server (NTRS)

Johnson, R. O.; Bushman, M. L.; Sherrill, W. M.

1980-01-01

Directionally resolved atmospheric radio frequency emission data were acquired from thunderstorms occurring in the central and southwestern United States. In addition, RF sferic tracking data were obtained from hurricanes and tropical depressions occurring in the Gulf of Mexico. The data were acquired using a crossed baseline phase interferometer operating at a frequency of 2.001 MHz. The received atmospherics were tested for phase linearity across the array, and azimuth/elevation angles of arrival were computed in real time. A histogram analysis of sferic burst count versus azimuth provided lines of bearing to centers of intense electrical activity. Analysis indicates a consistent capability of the phase linear direction finder to detect severe meteorological activity to distances of 2000 km from the receiving site. The technique evidences the ability to discriminate severe storms from nonsevere storms coexistent in large regional scale thunderstorm activity.

An Undergraduate Designed VLF Receiver: Findings from an Auroral Flight in Fairbanks, Alaska

NASA Astrophysics Data System (ADS)

Hernandez, E.; Behrend, C. C.; Fenton, A.; Mathur, S.; Greer, M.; Bering, E., III

2017-12-01

The fluctuating state of the D-region ionosphere creates electromagnetic oscillations in the very low frequency (VLF) range. These naturally occurring VLF waves, or sferics, can have distinct features and intensities which can be measured to describe state of the plasma in the D-region. These features are more prominent during geomagnetic events—such as the aurora. To investigate these waves, this team redesigned and fabricated a VLF receiver with an air-core loop antenna. The receiver was attached to a 1500-gram latex balloon and flown during a moderate auroral event on the 15th of March, 217 in Fairbanks, Alaska. Using MATLAB to make different graphs of the data, such as spectrograms, the sferics received on that night can be visualized and interpreted. Through the VLF spectrum, this poster will provide an interpretation of the D-region and describe the events of the flight (natural and manmade).

Spatial and Temporal Ionospheric Monitoring Using Broadband Sferic Measurements

NASA Astrophysics Data System (ADS)

McCormick, J. C.; Cohen, M. B.; Gross, N. C.; Said, R. K.

2018-04-01

The D region of the ionosphere (60-90 km altitude) is highly variable on timescales from fractions of a second to many hours, and on spatial scales up to many hundreds of kilometers. Very low frequency (VLF) and low-frequency (LF) (3-30 kHz and 30-300 kHz) radio waves are guided to global distances by reflections from the ground and the D region. Therefore, information about its current state is encoded in received VLF/LF signals. VLF transmitters have been used in the past for D region studies, with ionospheric disturbances manifesting as perturbations in amplitude and/or phase. The return stroke of lightning is an impulsive VLF radiator, but unlike VLF transmitters, lightning events are distributed broadly in space allowing for much greater spatial coverage of the D region compared to VLF transmitter-based remote sensing in addition to the broadband spectral advantage over the narrowband transmitters. The challenge is that individual lightning-generated waveforms, or "sferics," vary due to the lightning current parameters and uncertainty in the time/location information, in addition to D region ionospheric variability. These factors make it difficult to utilize the VLF/LF emissions from lightning in a straightforward manner. We describe a technique to recover the time domain and amplitude/phase spectra for both Bϕ and Br with high fidelity and consider the utility of our technique with ambient and varied ionospheric conditions. We demonstrate a technique to simulate sferics and infer a parameterized ionosphere with the Wait and Spies parameters (h' and β) offering all of the tools needed for a global measurement.

On the interactions between energetic electrons and lightning whistler waves observed at high L-shells on Van Allen Probes

NASA Astrophysics Data System (ADS)

Zheng, H.; Holzworth, R. H., II; Brundell, J. B.; Hospodarsky, G. B.; Jacobson, A. R.; Fennell, J. F.; Li, J.

2017-12-01

Lightning produces strong broadband radio waves, called "sferics", which propagate in the Earth-ionosphere waveguide and are detected thousands of kilometers away from their source. Global real-time detection of lightning strokes including their time, location and energy, is conducted with the World Wide Lightning Location Network (WWLLN). In the ionosphere, these sferics couple into very low frequency (VLF) whistler waves which propagate obliquely to the Earth's magnetic field. A good match has previously been shown between WWLLN sferics and Van Allen Probes lightning whistler waves. It is well known that lightning whistler waves can modify the distribution of energetic electrons in the Van Allen belts by pitch angle scattering into the loss cone, especially at low L-Shells (referred to as LEP - Lightning-induced Electron Precipitation). It is an open question whether lightning whistler waves play an important role at high L-shells. The possible interactions between energetic electrons and lightning whistler waves at high L-shells are considered to be weak in the past. However, lightning is copious, and weak pitch angle scattering into the drift or bounce loss cone would have a significant influence on the radiation belt populations. In this work, we will analyze the continuous burst mode EMFISIS data from September 2012 to 2016, to find out lightning whistler waves above L = 3. Based on that, MAGEIS data are used to study the related possible wave-particle interactions. In this talk, both case study and statistical analysis results will be presented.

Prevalent lightning sferics at 600 megahertz near Jupiter's poles

NASA Astrophysics Data System (ADS)

Brown, Shannon; Janssen, Michael; Adumitroaie, Virgil; Atreya, Sushil; Bolton, Scott; Gulkis, Samuel; Ingersoll, Andrew; Levin, Steven; Li, Cheng; Li, Liming; Lunine, Jonathan; Misra, Sidharth; Orton, Glenn; Steffes, Paul; Tabataba-Vakili, Fachreddin; Kolmašová, Ivana; Imai, Masafumi; Santolík, Ondřej; Kurth, William; Hospodarsky, George; Gurnett, Donald; Connerney, John

2018-06-01

Lightning has been detected on Jupiter by all visiting spacecraft through night-side optical imaging and whistler (lightning-generated radio waves) signatures1-6. Jovian lightning is thought to be generated in the mixed-phase (liquid-ice) region of convective water clouds through a charge-separation process between condensed liquid water and water-ice particles, similar to that of terrestrial (cloud-to-cloud) lightning7-9. Unlike terrestrial lightning, which emits broadly over the radio spectrum up to gigahertz frequencies10,11, lightning on Jupiter has been detected only at kilohertz frequencies, despite a search for signals in the megahertz range12. Strong ionospheric attenuation or a lightning discharge much slower than that on Earth have been suggested as possible explanations for this discrepancy13,14. Here we report observations of Jovian lightning sferics (broadband electromagnetic impulses) at 600 megahertz from the Microwave Radiometer15 onboard the Juno spacecraft. These detections imply that Jovian lightning discharges are not distinct from terrestrial lightning, as previously thought. In the first eight orbits of Juno, we detected 377 lightning sferics from pole to pole. We found lightning to be prevalent in the polar regions, absent near the equator, and most frequent in the northern hemisphere, at latitudes higher than 40 degrees north. Because the distribution of lightning is a proxy for moist convective activity, which is thought to be an important source of outward energy transport from the interior of the planet16,17, increased convection towards the poles could indicate an outward internal heat flux that is preferentially weighted towards the poles9,16,18. The distribution of moist convection is important for understanding the composition, general circulation and energy transport on Jupiter.

Fast low-level light pulses from the night sky observed with the SKYFLASH program

NASA Astrophysics Data System (ADS)

Winckler, J. R.; Franz, R. C.; Nemzek, R. J.

1993-05-01

This paper presents further discussion of and new data on fast subvisual increases in the luminosity of the night sky described in our previous papers. A detailed technical description of the simple telescopic photometers used in the project SKYFLASH and their mode of operation including the detection of polarized Rayleigh-scattered flashes is provided. Distant lightning storms account for many of the events, and the complex relations between short and long luminous pulses with and without sferics are shown by examples from a new computerized data system, supplemented by two low-light-level TV cameras. Of particular interest are the previously observed 'long' events having a slow rise and fall, 20-ms duration, and showing small polarization and no coincident sferic. A group of such events on September 22-23 during the invasion of U.S. coasts by Hurricane Hugo, is discussed in detail. The recently observed 'plume' cloud-top-to-stratosphere lightning event is suggested as a possible source type for these flashes. An alternative source may be exploding meteors, recently identified during SKYFLASH observations by low-light-level television techniques as the origin of some sky-wide flash events described herein.

Fast low-level light pulses from the night sky observed with the SKYFLASH program

NASA Technical Reports Server (NTRS)

Winckler, J. R.; Franz, R. C.; Nemzek, R. J.

1993-01-01

This paper presents further discussion of and new data on fast subvisual increases in the luminosity of the night sky described in our previous papers. A detailed technical description of the simple telescopic photometers used in the project SKYFLASH and their mode of operation including the detection of polarized Rayleigh-scattered flashes is provided. Distant lightning storms account for many of the events, and the complex relations between short and long luminous pulses with and without sferics are shown by examples from a new computerized data system, supplemented by two low-light-level TV cameras. Of particular interest are the previously observed 'long' events having a slow rise and fall, 20-ms duration, and showing small polarization and no coincident sferic. A group of such events on September 22-23 during the invasion of U.S. coasts by Hurricane Hugo, is discussed in detail. The recently observed 'plume' cloud-top-to-stratosphere lightning event is suggested as a possible source type for these flashes. An alternative source may be exploding meteors, recently identified during SKYFLASH observations by low-light-level television techniques as the origin of some sky-wide flash events described herein.

Midlatitude D region variations measured from broadband radio atmospherics

NASA Astrophysics Data System (ADS)

Han, Feng

The high power, broadband very low frequency (VLF, 3--30 kHz) and extremely low frequency (ELF, 3--3000 Hz) electromagnetic waves generated by lightning discharges and propagating in the Earth-ionosphere waveguide can be used to measure the average electron density profile of the lower ionosphere (D region) across the wave propagation path due to several reflections by the upper boundary (lower ionosphere) of the waveguide. This capability makes it possible to frequently and even continuously monitor the D region electron density profile variations over geographically large regions, which are measurements that are essentially impossible by other means. These guided waves, usually called atmospherics (or sferics for short), are recorded by our sensors located near Duke University. The purpose of this work is to develop and implement algorithms to derive the variations of D region electron density profile which is modeled by two parameters (one is height and another is sharpness), by comparing the recorded sferic spectra to a series of model simulated sferic spectra from using a finite difference time domain (FDTD) code. In order to understand the time scales, magnitudes and sources for the midlatitude nighttime D region variations, we analyzed the sferic data of July and August 2005, and extracted both the height and sharpness of the D region electron density profile. The heights show large temporal variations of several kilometers on some nights and the relatively stable behavior on others. Statistical calculations indicate that the hourly average heights during the two months range between 82.0 km and 87.2 km with a mean value of 84.9 km and a standard deviation of 1.1 km. We also observed spatial variations of height as large as 2.0 km over 5 degrees latitudes on some nights, and no spatial variation on others. In addition, the measured height variations exhibited close correlations with local lightning occurrence rate on some nights but no correlation with local lightning or displaced lightning on others. The nighttime profile sharpness during 2.5 hours in two different nights was calculated, and the results were compared to the equivalent sharpness derived from International Reference Ionosphere (IRI) models. Both the absolute values and variation trends in IRI models are different from those in broadband measurements. Based on sferic data similar to those for nighttime, we also measured the day-time D region electron density profile variations in July and August 2005 near Duke University. As expected, the solar radiation is the dominant but not the only determinant source for the daytime D region profile height temporal variations. The observed quiet time heights showed close correlations with solar zenith angle changes but unexpected spatial variations not linked to the solar zenith angle were also observed on some days, with 15% of days exhibiting regional differences larger than 0.5 km. During the solar flare, the induced height change was approximately proportional to the logarithm of the X-ray fluxes. During the rising and decaying phases of the solar flare, the height changes correlated more consistently with the short (wavelength 0.5--4 A), rather than the long (wavelength 1--8 A) X-ray flux changes. The daytime profile sharpness during morning, noontime and afternoon periods in three different days and for the solar zenith angle range 20 to 75 degrees was calculated. These broadband measured results were compared to narrowband VLF measurements, IRI models and Faraday rotation base IRI models (called FIRI). The estimated sharpness from all these sources was more consistent when the solar zenith angle was small than when it was large. By applying the nighttime and daytime measurement techniques, we also derived the D region variations during sunrise and sunset periods. The measurements showed that both the electron density profile height and sharpness decrease during the sunrise period while increase during the sunset period.

D-region Ionospheric Imaging Using VLF/LF Broadband Sferics, Forward Modeling, and Tomography

NASA Astrophysics Data System (ADS)

McCormick, J.; Cohen, M.

2017-12-01

The D-region of the ionosphere (60-90 km altitude) is highly variable on timescales from fractions of a second to many hours, and on spatial scales from 10 km to many hundreds of km. VLF and LF (3-30kHz, 30-300kHz) radio waves are guided to global distances by reflecting off of the ground and the D-region, making the Earth-ionosphere waveguide (EIWG). Therefore, information about the current state of the ionosphere is encoded in received VLF/LF radio waves since they act like probes of the D-region. The return stroke of lightning is an impulsive event that radiates powerful broadband radio emissions in VLF/LF bands known as `radio atmospherics' or `sferics'. Lightning flashes occur about 40-50 times per second throughout the Earth. An average of 2000 lightning storms occur each day with a mean duration of 30 minutes creating a broad spatial and temporal distribution of lightning VLF/LF sources. With careful processing, we can recover high fidelity measurements of amplitude and phase of both the radial and azimuthal magnetic field sferic components. By comparison to a theoretical EIWG propagation model such as the Long Wave Propagation Capability (LWPC) developed by the US Navy, with a standard forward modeling approach, we can infer information about the current state of the D-region. Typically, the ionosphere is parametrized to reduce the dimensionality of the problem which usually results in an electron density vs altitude profile. For large distances (Greater than 1000 km), these results can be interpreted as path-averaged information. In contrast to studies using navy transmitters to study the D-region, the full spectral information allows for more complete information and less ambiguous inferred ionospheric parameters. With the spatial breadth of lightning sources taken together with a broadly distributed VLF/LF receiver network, a dense set of measurements are acquired in a tomographic sense. Using the wealth of linear algebra and imaging techniques it is possible to produce a 2D image of the D-region electron density profile.

Chasing Lightning: Sferics, Tweeks and Whistlers

NASA Astrophysics Data System (ADS)

Webb, P. A.; Franzen, K.; Garcia, L.; Schou, P.; Rous, P.

2008-12-01

We all know what lightning looks like during a thunderstorm, but the visible flash we see is only part of the story. This is because lightning also generates light with other frequencies that we cannot perceive with our eyes, but which are just as real as visible light. Unlike the visible light from lightning, these other frequencies can carry the lightning's energy hundreds or thousands of miles across the surface of the Earth in the form of special signals called "tweeks" and "sferics". Some of these emissions can even travel tens of thousands of miles out into space before returning to the Earth as "whistlers". The INSPIRE Project, Inc is a non-profit scientific and educational corporation whose beginning mission was to bring the excitement of observing these very low frequency (VLF) natural radio waves emissions from lightning to high school students. Since 1989, INSPIRE has provided specially designed radio receiver kits to over 2,600 participants around the world to make observations of signals in the VLF frequency range. Many of these participants are using the VLF data they collect in very creative projects that include fiction, music and art exhibitions. During the Fall 2008 semester, the first INSPIRE based university-level course was taught at University of Maryland Baltimore County (UMBC) as part of its First-Year Seminar (FYS) series. The FYS classes are limited to 20 first-year students per class and are designed to create an active-learning environment that encourages student participation and discussion that might not otherwise occur in larger first-year classes. This presentation will cover the experiences gained from using the INSPIRE kits as the basis of a university course. This will include the lecture material that covers the basic physics of lightning, thunderstorms and the Earth's atmosphere, as well as the electronics required to understand the basic workings of the VLF kit. It will also cover the students assembly of the kit in an electronics lab (some soldering required!) and the subsequent field trips to local sites to listen for the sferics, tweeks and whistlers using the assembled kit, followed by data analysis and the writing of reports on the observations.

Comparison between model predictions and observations of ELF radio atmospherics generated by rocket-triggered lightning

NASA Astrophysics Data System (ADS)

Dupree, N. A.; Moore, R. C.

2011-12-01

Model predictions of the ELF radio atmospheric generated by rocket-triggered lightning are compared with observations performed at Arrival Heights, Antarctica. The ability to infer source characteristics using observations at great distances may prove to greatly enhance the understanding of lightning processes that are associated with the production of transient luminous events (TLEs) as well as other ionospheric effects associated with lightning. The modeling of the sferic waveform is carried out using a modified version of the Long Wavelength Propagation Capability (LWPC) code developed by the Naval Ocean Systems Center over a period of many years. LWPC is an inherently narrowband propagation code that has been modified to predict the broadband response of the Earth-ionosphere waveguide to an impulsive lightning flash while preserving the ability of LWPC to account for an inhomogeneous waveguide. ELF observations performed at Arrival Heights, Antarctica during rocket-triggered lightning experiments at the International Center for Lightning Research and Testing (ICLRT) located at Camp Blanding, Florida are presented. The lightning current waveforms directly measured at the base of the lightning channel (at the ICLRT) are used together with LWPC to predict the sferic waveform observed at Arrival Heights under various ionospheric conditions. This paper critically compares observations with model predictions.

Monitoring D-Region Variability from Lightning Measurements

NASA Technical Reports Server (NTRS)

Simoes, Fernando; Berthelier, Jean-Jacques; Pfaff, Robert; Bilitza, Dieter; Klenzing, Jeffery

2011-01-01

In situ measurements of ionospheric D-region characteristics are somewhat scarce and rely mostly on sounding rockets. Remote sensing techniques employing Very Low Frequency (VLF) transmitters can provide electron density estimates from subionospheric wave propagation modeling. Here we discuss how lightning waveform measurements, namely sferics and tweeks, can be used for monitoring the D-region variability and day-night transition, and for local electron density estimates. A brief comparison among D-region aeronomy models is also presented.

ELF Sferics Produced by Rocket-Triggered Lightning and Observed at Great Distances

NASA Astrophysics Data System (ADS)

Dupree, N. A.; Moore, R. C.; Fraser-Smith, A. C.

2013-12-01

Experimental observations of ELF radio atmospherics produced by rocket-triggered lightning flashes are used to analyze Earth-ionosphere waveguide excitation and propagation characteristics as a function of return stroke. Rocket-triggered lightning experiments are performed at the International Center for Lightning Research and Testing (ICLRT) located at Camp Blanding, Florida. Long-distance ELF observations are performed in California, Greenland, and Antarctica, although this work focuses on observations performed in Greenland. The lightning current waveforms directly measured at the base of the lightning channel (at the ICLRT) are used together with the Long Wavelength Propagation Capability (LWPC) code to predict the sferic waveform observed at the receiver locations under various ionospheric conditions. LWPC was developed by the Naval Ocean Systems Center over a period of many years. It is an inherently narrowband propagation code that has been modified to predict the broadband response of the Earth-ionosphere waveguide to an impulsive lightning flash while preserving the ability of LWPC to account for an inhomogeneous waveguide. This paper critically compares observations with model predictions, and in particular analyzes Earth-ionosphere waveguide excitation as a function of return stroke. The ability to infer source characteristics using observations at great distances may prove to greatly enhance the understanding of lightning processes that are associated with the production of transient luminous events (TLEs) as well as other ionospheric effects associated with lightning.

Unusually high frequency natural VLF radio emissions observed during daytime in Northern Finland

NASA Astrophysics Data System (ADS)

Manninen, Jyrki; Turunen, Tauno; Kleimenova, Natalia; Rycroft, Michael; Gromova, Liudmila; Sirviö, Iina

2016-12-01

Geomagnetic field variations and electromagnetic waves of different frequencies are ever present in the Earth’s environment in which the Earth’s fauna and flora have evolved and live. These waves are a very useful tool for studying and exploring the physics of plasma processes occurring in the magnetosphere and ionosphere. Here we present ground-based observations of natural electromagnetic emissions of magnetospheric origin at very low frequency (VLF, 3-30 kHz), which are neither heard nor seen in their spectrograms because they are hidden by strong impulsive signals (sferics) originating in lightning discharges. After filtering out the sferics, peculiar emissions are revealed in these digital recordings, made in Northern Finland, at unusually high frequencies in the VLF band. These recently revealed emissions, which are observed for several hours almost every day in winter, contain short (˜1-3 min) burst-like structures at frequencies above 4-6 kHz, even up to 15 kHz; fine structure on the 1 s time scale is also prevalent. It seems that these whistler mode emissions are generated deep inside the magnetosphere, but the detailed nature, generation region and propagation behaviour of these newly discovered high latitude VLF emissions remain unknown; however, further research on them may shed new light on wave-particle interactions occurring in the Earth’s radiation belts.

Selected results from the ISUAL/FORMOSAT2 mission in a 12-year journey

NASA Astrophysics Data System (ADS)

Chen, A. B. C.; Hsu, R. R.; Su, H. T.; Huang, S. M.; Lee, L. J.; Chou, J. K.; Chang, S. C.; Wu, Y. J.; Peng, K. M.; Liu, T. Y.; Mende, S. B.; Frey, H. U.; Takahashi, Y.; Lee, L. C.

2016-12-01

The ISUAL (Imager of Sprites and Upper Atmospheric Lightning) is a scientific payload onboard the FORMOSAT2 satellite (FS2). It is also the first satellite project with the global survey of transient luminous events (TLEs) as one of the mission objectives. Since the launch of ISUAL/FS2 in 2004, ISUAL has continuously monitored the occurrence of TLEs over the pre-midnight tropical and subtropical regions in the past 12 years until 20 June 2016, due to the failure of two of the four reaction wheels. In her 12-year journey, more than forty-two thousand of TLEs, including the sub-species like elves, sprites, sprite-halos, blue jets and gigantic jets, have been recorded from this space platform. In the meantime, as the supporting facilities to the space-borne ISUAL experiment, ground optical imagery systems have been deployed to observe TLEs occurring near Taiwan and several radio waves detecting ground stations have also been installed to register the lightning- or the TLE-related sferics. From analyzing the observed events and the associated sferics, some important insights on these intriguing thundercloud-top phenomena have been revealed. In this talk, the occurrence, the global distributions, the occurrence rates, and the physical characteristics of TLEs as well as some salient properties of the TLE-producing lightning and the impacts of TLEs on the upper atmosphere revealed by the ISUAL mission will be concisely discussed and summarized.

Classification and machine recognition of severe weather patterns

NASA Technical Reports Server (NTRS)

Wang, P. P.; Burns, R. C.

1976-01-01

Forecasting and warning of severe weather conditions are treated from the vantage point of pattern recognition by machine. Pictorial patterns and waveform patterns are distinguished. Time series data on sferics are dealt with by considering waveform patterns. A severe storm patterns recognition machine is described, along with schemes for detection via cross-correlation of time series (same channel or different channels). Syntactic and decision-theoretic approaches to feature extraction are discussed. Active and decayed tornados and thunderstorms, lightning discharges, and funnels and their related time series data are studied.

Fermi GBM Observations of Terrestrial Gamma Flashes

NASA Technical Reports Server (NTRS)

Wilson-Hodge, Colleen A.; Briggs, M. S.; Connaughton, V.; Fishman, G. J.; Bhat, P. N.; Paciesas, W. S.; Preece, R. D.; Kippen, R. M.; vonKienlin, A.; Dwyer, J. R.;

Terrestrial Gamma Ray Flashes due to Particle Acceleration in Tropical Storm Systems

NASA Technical Reports Server (NTRS)

Roberts, O. S.; Fitzpatrick, G.; Priftis, G.; Bedka, K.; Chronis, T.; Mcbreen, S.; Briggs, M.; Cramer, E.; Mailyan, B.; Stanbro, M.

2017-01-01

Terrestrial gamma ray flashes (TGFs) are submillisecond flashes of energetic radiation that are believed to emanate from intracloud lightning inside thunderstorms. This emission can be detected hundreds of kilometers from the source by space-based observatories such as the Fermi Gamma-ray Space Telescope (Fermi). The location of the TGF-producing storms can be determined using very low frequency (VLF) radio measurements made simultaneously with the Fermi detection, allowing additional insight into the mechanisms which produce these phenomena. In this paper, we report 37 TGFs originating from tropical storm systems for the first time. Previous studies to gain insight into how tropical cyclones formed and how destructive they can be include the investigation of lightning flash rates and their dependence on storm evolution. We find TGFs to emanate from a broad range of distances from the storm centers. In hurricanes and severe tropical cyclones, the TGFs are observed to occur predominately from the outer rainbands. A majority of our sample also show TGFs occurring during the strengthening phase of the encompassing storm system. These results verify that TGF production closely follows when and where lightning predominately occurs in cyclones. The intrinsic characteristics of these TGFs were not found to differ from other TGFs reported in larger samples. We also find that some TGF-producing storm cells in tropical storm systems far removed from land have a low number of WWLLN sferics. Although not unique to tropical cyclones, this TGF/sferic ratio may imply a high efficiency for the lightning in these storms to generate TGFs.

WWLLN and Earth Networks new combined Global Lightning Network: First Look

NASA Astrophysics Data System (ADS)

Holzworth, R. H., II; Brundell, J. B.; Sloop, C.; Heckman, S.; Rodger, C. J.

2016-12-01

Lightning VLF sferic waveforms detected around the world by WWLLN (World Wide Lightning Location Network) and by Earth Networks WTLN receivers are being analyzed in real time to calculate the time of group arrival (TOGA) of the sferic wave packet at each station. These times (TOGAs) are then used for time-of-arrival analysis to determine the source lightning location. Beginning in 2016 we have successfully implemented the operational software to allow the incorporation of waveforms from hundreds of Earth Networks sensors into the normal WWLLN TOGA processing, resulting in a new global lightning distribution which has over twice as many stroke locations as the WWLLN-only data set. The combined global lightning network shows marked improvement over the WWLLN-only data set in regions such as central and southern Africa, and over the Indian subcontinent. As of July 2016 the new data set is typically running at about 230% of WWLLN-only in terms of total strokes, and some days over 250%, using data from 65 to 70 WWLLN stations, combined with the VLF channel from about 160 Earth Networks stations. The Earth Networks lightning network includes nearly 1000 receiving stations, so it is anticipated we will be able to further increase the total stations being used for the new combined network while still maintaining a relatively smooth global distribution of the sensors. Detailed comparisons of the new data set with WWLLN-only data, as well as with independent lightning location networks including WTLN in the CONUS and NZLDN in New Zealand will be presented.

An Event Observed as a Terrestrial Gamma-ray Flash (TGF) and a Terrestrial Electron Beam (TEB) by Fermi GBM

NASA Astrophysics Data System (ADS)

Stanbro, M.; Briggs, M. S.; Cramer, E.; Dwyer, J. R.; Roberts, O.

2017-12-01

Terrestrial Gamma-ray Flashes (TGFs) are sub-ms, intense flashes of gamma-rays. They are due to the acceleration of electrons with relativistic energies in thunderstorms that emit gamma-rays via bremsstrahlung. When these photons reach the upper atmosphere, they can produce secondary electrons and positrons that escape the atmosphere and propagate along the Earth's magnetic field line. Space instruments can detect these charged particles, known as Terrestrial Electron Beams (TEBs), after traveling thousands of kilometers from the thunderstorm. We present an event that was observed by the Fermi Gamma-ray Burst Monitor (GBM) as both a TGF and a TEB. To our knowledge this is the first such event that has ever been observed. We interpret the first pulse as a TGF with a duration of 0.2 ms. After 0.5 ms a second pulse is seen with a duration of 2 ms that we interpret as a TEB. Confirming this interpretation, a third pulse is seen 90 ms later, which is understood as a TEB magnetic mirror pulse. The World Wide Lightning Location Network (WWLLN) and the Earth Networks Total Lightning Network (ENTLN) detected a sferic, under the spacecraft footprint and within the southern magnetic footprint that is simultaneous with the first pulse. Along with the sferic, this unique observation allows us for the first time to test TGF and TEB models for the same event. We present Monte Carlo simulations of the first two pulses, including pitch angles for electrons and positrons, to see if the models can consistently describe the TGF/TEB spectra and time profiles originating from the same source.

Building and Testing a Portable VLF Receiver

NASA Technical Reports Server (NTRS)

McLaughlin, Robert; Krause, L.

2014-01-01

Unwanted emissions or signal noise is a major problem for VLF radio receivers. These can occur from man made sources such as power line hum, which can be prevalent for many harmonics after the fundamental 50 or 60 Hz AC source or from VLF radio transmissions such as LORAN, used for navigation and communications. Natural emissions can also be detrimental to the quality of recordings as some of the more interesting natural emissions such as whistlers or auroral chorus may be drowned out by the more common sferic emissions. VLF receivers must selectively filter out unwanted emissions and amplify the filtered signal to a record-able level without degrading the quality.

A case study of lightning, whistlers, and associated ionospheric effects during a substorm particle injection event

NASA Technical Reports Server (NTRS)

Rodriguez, J. V.; Inan, U. S.; Li, Y. Q.; Holzworth, R. H.; Smith, A. J.; Orville, R. E.; Rosenberg, T. J.

1992-01-01

The relationships among cloud-to-ground (CG) lightning, sferics, whistlers, VLF amplitude perturbations, and other ionospheric phenomena occurring during substorm events were investigated using data from simultaneous ground-based observations of narrow-band and broad-band VLF radio waves and of CG lightning made during the 1987 Wave-Induced Particle Precipitation campaign conducted from Wallops Island (Virginia). Results suggest that the data collected on ionospheric phenomena during this event may represent new evidence of direct coupling of lightning energy to the lower ionosphere, either in conjunction with or in the absence of gyroresonant interactions between whistler mode waves and electrons in the magnetosphere.

Estimated intensity of the EMP from lightning discharges necessary for elves initiation based on balloon experiment

NASA Astrophysics Data System (ADS)

Kondo, S.; Yoshida, A.; Takahashi, Y.; Chikada, S.; Adachi, T.; Sakanoi, T.

2007-12-01

Transient optical phenomena in the mesosphere and lower ionosphere called transient luminous events (TLEs) have been investigated extensively since the first discovery in 1989. In the lower ionosphere, elves are generated by the electromagnetic pulses (EMPs) radiated from the intense lightning current. On the ground-based observation, cameras can not always identify the occurrence of elves because elves emission is sometimes reduced significantly by the atmosphere and blocked by clouds. Therefore, it has been difficult to determine the threshold of intensity of EMPs necessary for initiation of elves. We simultaneously carried out optical and sferics measurements for TLEs and lightning discharges using a high altitude balloon launched at Sanriku Balloon Center on the night of August 25 / 26 in 2006. We fixed four CCD cameras on the gondola, each of which had horizontal FOV of ~100 degree. They cover 360 degree in horizontal direction and imaged the TLEs without atmospheric extinction nor blocking by clouds. The frame rate is 30 fps. We installed three dipole antennas at the gondola, which received the vertical and horizontal electric fields radiated from lightning discharges. The frequency range of the VLF receiver is 1-25 kHz. We also make use of VLF sferics data obtained by ground-based antennas located at Tohoku University in Sendai. We picked up six elves from the image data set obtained by the CCD cameras, and examined the maximum amplitudes of the vertical electric field for 22 lightning discharge events including the six elves events observed both at the balloon and at Sendai. It is found that the maximum amplitudes of the vertical electric field in the five elves events are much larger than those in the other lightning events. We estimate the intensity of the radiated electric field necessary for elves. About one elves event, we don't see intense vertical electric field in the balloon data.

Fermi GBM Observations of Terrestrial Gamma Flashes

NASA Technical Reports Server (NTRS)

Wilson-Hodge, Colleen A.; Briggs, M. S.; Fishman, G. J.; Bhat, P. N.; Paciesas, W. S.; Preece, R.; Kippen, R. M.; von Kienlin, A.; Dwyer, J. R.; Smith, D. M.;

Television image of a large upward electrical discharge above a thunderstorm system

NASA Technical Reports Server (NTRS)

Franz, R. C.; Nemzek, R. J.; Winckler, J. R.

1990-01-01

A low light-level TV camera is used to obtain an unusual image of luminous electrical discharge over a thunderstorm 250 km from the observation site. The image is presented and the discharge in the image is described. It is suggested that the image is probably due to two localized electric charge concentrations at the cloud tops. The hazard of these discharges for aircraft and rocket launches is examined. Consideration is given to the possibility that these discharges may account for unexplained photometric observations of distant lightning events that show a low rise rate of the luminous pulse and no electromagnetic sferic pulse like that in cloud-to-earth lightning strokes. The photometric events of this type that occurred on September 22-23, 1989 during hurricane Hugo are noted.

Lightning-generated whistler waves observed by probes on the Communication/Navigation Outage Forecast System satellite at low latitudes

NASA Astrophysics Data System (ADS)

Holzworth, R. H.; McCarthy, M. P.; Pfaff, R. F.; Jacobson, A. R.; Willcockson, W. L.; Rowland, D. E.

2011-06-01

Direct evidence is presented for a causal relationship between lightning and strong electric field transients inside equatorial ionospheric density depletions. In fact, these whistler mode plasma waves may be the dominant electric field signal within such depletions. Optical lightning data from the Communication/Navigation Outage Forecast System (C/NOFS) satellite and global lightning location information from the World Wide Lightning Location Network are presented as independent verification that these electric field transients are caused by lightning. The electric field instrument on C/NOFS routinely measures lightning-related electric field wave packets or sferics, associated with simultaneous measurements of optical flashes at all altitudes encountered by the satellite (401-867 km). Lightning-generated whistler waves have abundant access to the topside ionosphere, even close to the magnetic equator.

Lightning-Generated Whistler Waves Observed by Probes On The Communication/Navigation Outage Forecast System Satellite at Low Latitudes

NASA Technical Reports Server (NTRS)

Holzworth, R. H.; McCarthy, M. P.; Pfaff, R. F.; Jacobson, A. R.; Willcockson, W. L.; Rowland, D. E.

2011-01-01

Direct evidence is presented for a causal relationship between lightning and strong electric field transients inside equatorial ionospheric density depletions. In fact, these whistler mode plasma waves may be the dominant electric field signal within such depletions. Optical lightning data from the Communication/Navigation Outage Forecast System (C/NOFS) satellite and global lightning location information from the World Wide Lightning Location Network are presented as independent verification that these electric field transients are caused by lightning. The electric field instrument on C/NOFS routinely measures lightning ]related electric field wave packets or sferics, associated with simultaneous measurements of optical flashes at all altitudes encountered by the satellite (401.867 km). Lightning ]generated whistler waves have abundant access to the topside ionosphere, even close to the magnetic equator.

Research instrumentation for tornado electromagnetics emissions detection

NASA Technical Reports Server (NTRS)

Jenkins, H. H.; Wilson, C. S.

1977-01-01

Instrumentation for receiving, processing, and recording HF/VHF electromagnetic emissions from severe weather activity is described. Both airborne and ground-based instrumentation units are described on system and subsystem levels. Design considerations, design decisions, and the rationale behind the decisions are given. Performance characteristics are summarized and recommendations for improvements are given. The objectives, procedures, and test results of the following are presented: (1) airborne flight test in the Midwest U.S.A. (Spring 1975) and at the Kennedy Space Center, Florida (Summer 1975); (2) ground-based data collected in North Georgia (Summer/Fall 1975); and (3) airborne flight test in the Midwest (late Spring 1976) and at the Kennedy Space Center, Florida (Summer 1976). The Midwest tests concentrated on severe weather with tornadic activity; the Florida and Georgia tests monitored air mass convective thunderstorm characteristics. Supporting ground truth data from weather radars and sferics DF nets are described.

Enhanced detection of terrestrial gamma-ray flashes by AGILE.

PubMed

Marisaldi, M; Argan, A; Ursi, A; Gjesteland, T; Fuschino, F; Labanti, C; Galli, M; Tavani, M; Pittori, C; Verrecchia, F; D'Amico, F; Østgaard, N; Mereghetti, S; Campana, R; Cattaneo, P W; Bulgarelli, A; Colafrancesco, S; Dietrich, S; Longo, F; Gianotti, F; Giommi, P; Rappoldi, A; Trifoglio, M; Trois, A

2015-11-16

At the end of March 2015 the onboard software configuration of the Astrorivelatore Gamma a Immagini Leggero (AGILE) satellite was modified in order to disable the veto signal of the anticoincidence shield for the minicalorimeter instrument. The motivation for such a change was the understanding that the dead time induced by the anticoincidence prevented the detection of a large fraction of Terrestrial Gamma-Ray Flashes (TGFs). The configuration change was highly successful resulting in an increase of one order of magnitude in TGF detection rate. As expected, the largest fraction of the new events has short duration (<100 μs), and part of them has simultaneous association with lightning sferics detected by the World Wide Lightning Location Network. The new configuration provides the largest TGF detection rate surface density (TGFs/km 2 /yr) to date, opening prospects for improved correlation studies with lightning and atmospheric parameters on short spatial and temporal scales along the equatorial region.

Television Image of a Large Upward Electrical Discharge Above a Thunderstorm System

NASA Astrophysics Data System (ADS)

Franz, R. C.; Nemzek, R. J.; Winckler, J. R.

1990-07-01

An image of an unusual luminous electrical discharge over a thunderstorm 250 kilometers from the observing site has been obtained with a low-light-level television camera. The discharge began at the cloud tops at 14 kilometers and extended into the clear air 20 kilometers higher. The image, which had a duration of less than 30 milliseconds, resembled two jets or fountains and was probably caused by two localized electric charge concentrations at the cloud tops. Large upward discharges may create a hazard for aircraft and rocket launches and, by penetrating into the ionosphere, may initiate whistler waves and other effects on a magnetospheric scale. Such upward electrical discharges may account for unexplained photometric observations of distant lightning events that showed a low rise rate of the luminous pulse and no electromagnetic sferic pulse of the type that accompanies cloud-to-earth lightning strokes. An unusually high rate of such photometric events was recorded during the night of 22 to 23 September 1989 during a storm associated with hurricane Hugo.

Television image of a large upward electrical discharge above a thunderstorm system.

PubMed

Franz, R C; Nemzek, R J; Winckler, J R

1990-07-06

An image of an unusual luminous electrical discharge over a thunderstorm 250 kilometers from the observing site has been obtained with a low-light-level television camera. The discharge began at the cloud tops at 14 kilometers and extended into the clear air 20 kilometers higher. The image, which had a duration of less than 30 milliseconds,resembled two jets or fountains and was probably caused by two localizd electric charge concentrations at the cloud tops. Large upward discharges may create a hazard for aircraft and rocket launches and, by penetrating into the ionosphere, may initiate whistler waves and other effects on a magnetospheric scale. Such upward electrical discharges may account for unexplained photometric observations of distant lightning events that showed a low rise rate of the luminous pulse and no electromagnetic sferic pulse of the type that accompanies cloud-to-earth lightning strokes. An unusually high rate of such photometric events was recorded during the night of 22 to 23 September 1989 during a storm associated with hurricane Hugo.

Analysis of ELF Radio Atmospherics Radiated by Rocket-Triggered Lightning

NASA Astrophysics Data System (ADS)

Dupree, N. A.; Moore, R. C.; Pilkey, J. T.; Uman, M. A.; Jordan, D. M.; Caicedo, J. A.; Hare, B.; Ngin, T. K.

2014-12-01

Experimental observations of ELF radio atmospherics produced by rocket-triggered lightning flashes are used to analyze Earth-ionosphere waveguide excitation and propagation characteristics. Rocket-triggered lightning experiments are performed at the International Center for Lightning Research and Testing (ICLRT) located at Camp Blanding, Florida. Long-distance ELF observations are performed in California, Greenland, and Antarctica. The lightning current waveforms directly measured at the base of the lightning channel (at the ICLRT) along with pertinent Lightning Mapping Array (LMA) data are used together with the Long Wavelength Propagation Capability (LWPC) code to predict the radio atmospheric (sferic) waveform observed at the receiver locations under various ionospheric conditions. We identify fitted exponential electron density profiles that accurately describe the observed propagation delays, phase delays, and signal amplitudes. The ability to infer ionospheric characteristics using distant ELF observations greatly enhances ionospheric remote sensing capabilities, especially in regard to interpreting observations of transient luminous events (TLEs) and other ionospheric effects associated with lightning.

Geometrical Effects on the Electromagnetic Radiation from Lightning Return Strokes

NASA Technical Reports Server (NTRS)

Willett, John C.; Smith, David A.; LeVine, David M.; Zukor, Dorothy J. (Technical Monitor)

2000-01-01

The Los Alamos National Laboratory (LANL) Sferic Array has recorded electric-field-change waveforms simultaneously at several stations surrounding the ground-strike points of numerous return strokes in cloud-to-ground lightning flashes. Such data are available from the five-station sub-networks in both Florida and New Mexico. With these data it has been possible for the first time to compare the waveforms radiated in different directions by a given stroke. Such comparisons are of interest to assess both the effects of channel geometry on the fine structure of subsequent-stroke radiation fields and the role of branches in the more jagged appearance of first-stroke waveforms. This paper presents multiple-station, time-domain waveforms with a 200 Hz to 500 kHz pass-band from both first and subsequent return strokes at ranges generally between 100 and 200 km. The differences among waveforms of the same stroke received at stations in different directions from the lightning channel are often obvious. These differences are illustrated and interpreted in the context of channel tortuosity and branches.

ELF/VLF Wave Generation and Scattering from Modulated Heating of the Ionosphere at Arecibo Observatory

NASA Astrophysics Data System (ADS)

Maxworth, A. S.; Golkowski, M.; McCormick, J.; Cohen, M.; Hosseini, P.; Bittle, J.

2017-12-01

The recently completed ionospheric heater at Arecibo Observatory is used for modulated HF (5 or 8 MHz) heating of the ionosphere, to generate ELF/VLF (3 Hz - 30 kHz) waves. Observation of ramp and tone signals at frequencies from hundreds of Hz to several kHz at multiple receivers confirms the ability of the heater to modulate D region currents and create an ELF/VLF antenna in the ionosphere. Observed ELF/VLF signal amplitudes are lower than for similar experiments performed at high latitudes at the HAARP and Tromso facilities, for a variety of reasons including the reduced natural currents at mid latitudes, and the lower HF power of the Arecibo heater. The heating of the overhead ionosphere is also observed to change the Earth-ionosphere waveguide propagation characteristics as is evident from simultaneous observations of lightning induced sferics and VLF transmitter signals that propagate under the heated region. The active heating of the ionosphere modifies the reflection of incident VLF (3-30 kHz) waves. We present initial observations of HF heating of the D-region and resulting ELF/VLF wave generation.

VLF and HF Plasma Waves Associated with Spread-F Plasma Depletions Observed on the C/NOFS Satellite

NASA Technical Reports Server (NTRS)

Pfaff, Robert; Freudenreich, H.; Schuck, P.; Klenzing, J.

2011-01-01

The C/NOFS spacecraft frequently encounters structured plasma depletions associated with equatorial spread-F along its trajectory that varies between 401 km perigee and 867 km apogee in the low latitude ionosphere. We report two classes of plasma waves detected with the Vector Electric Field Investigation (VEFI) that appear when the plasma frequency is less than the electron gyro frequency, as is common in spread-F depletions where the plasma number density typically decreases below 10(exp 4)/cu cm. In these conditions, both broadband VLF waves with a clear cutoff at the lower hybrid frequency and broadband HF waves with a clear cutoff at the plasma frequency are observed. We interpret these waves as "hiss-type" emissions possibly associated with the flow of suprathermal electrons within the inter-hemispherical magnetic flux tubes. We also report evidence of enhanced wave "transients" sometimes embedded in the broader band emissions that are associated with lightning sferics detected within the depleted plasma regions that appear in both the VLF and HF data. Theoretical implications of these observations are discussed.

FORTE Compact Intra-cloud Discharge Detection parameterized by Peak Current

NASA Astrophysics Data System (ADS)

Heavner, M. J.; Suszcynsky, D. M.; Jacobson, A. R.; Heavner, B. D.; Smith, D. A.

2002-12-01

The Los Alamos Sferic Array (EDOT) has recorded over 3.7 million lightning-related fast electric field change data records during April 1 - August 31, 2001 and 2002. The events were detected by three or more stations, allowing for differential-time-of-arrival location determination. The waveforms are characterized with estimated peak currents as well as by event type. Narrow Bipolar Events (NBEs), the VLF/LF signature of Compact Intra-cloud Discharges (CIDs), are generally isolated pulses with identifiable ionospheric reflections, permitting determination of event source altitudes. We briefly review the EDOT characterization of events. The FORTE satellite observes Trans-Ionospheric Pulse Pairs (TIPPs, the VHF satellite signature of CIDs). The subset of coincident EDOT and FORTE CID observations are compared with the total EDOT CID database to characterize the VHF detection efficiency of CIDs. The NBE polarity and altitude are also examined in the context of FORTE TIPP detection. The parameter-dependent detection efficiencies are extrapolated from FORTE orbit to GPS orbit in support of the V-GLASS effort (GPS based global detection of lightning).

The first AGILE low-energy (< 30 MeV) Terrestrial Gamma-ray Flashes catalog

NASA Astrophysics Data System (ADS)

Marisaldi, Martino; Fuschino, Fabio; Pittori, Carlotta; Verrecchia, Francesco; Giommi, Paolo; Tavani, Marco; Dietrich, Stefano; Price, Colin; Argan, Andrea; Labanti, Claudio; Galli, Marcello; Longo, Francesco; Del Monte, Ettore; Barbiellini, Guido; Giuliani, Andrea; Bulgarelli, Andrea; Gianotti, Fulvio; Trifoglio, Massimo; Trois, Alessio

2014-05-01

We present the first catalog of Terrestrial Gamma-ray Flashes (TGFs) detected by the Minicalorimeter (MCAL) instrument on-board the AGILE satellite. The catalog includes 308 TGFs detected during the period March 2009 - July 2012 in the +/- 2.5° latitude band and selected to have the maximum photon energy up to 30 MeV. The characteristics of the AGILE events are analysed and compared to the observational framework established by the two other currently active missions capable of detecting TGFs from space, RHESSI and Fermi. A detailed model of the MCAL dead time is presented, which is fundamental to properly interpret our observations, particularly concerning duration, intensity and correlation with lightning sferics detected by the World Wide Lightning Location Network. The TGFs cumulative spectrum supports a low production altitude, in agreement with previous measurements. The AGILE TGF catalog below 30 MeV is publicly accessible online at the website of the ASI Science Data Center (ASDC) http://www.asdc.asi.it/mcaltgfcat/ In addition to the TGF sample properties we also present the catalog website functionalities available to users.

VLF long-range lightning location using the arrival time difference technique (ATD)

NASA Technical Reports Server (NTRS)

Ierkic, H. Mario

1996-01-01

A new network of VLF receiving systems is currently being developed in the USA to support NASA's Tropical Rain Measuring Mission (TRMM). The new network will be deployed in the east coast of the US, including Puerto Rico, and will be operational in late 1995. The system should give affordable, near real-time, accurate lightning locating capabilities at long ranges and with extended coverage. It is based on the Arrival Time Difference (ATD) method of Lee (1986; 1990). The ATD technique is based on the estimation of the time of arrival of sferics detected over an 18 kHz bandwith. The ground system results will be compared and complemented with satellite optical measurements gathered with the already operational Optical Transient Detector (OTD) instrument and in due course with its successor the Lightning Imaging Sensor (LIS). Lightning observations are important to understand atmospheric electrification phenomena, discharge processes, associated phenomena on earth (e.g. whistlers, explosive Spread-F) and other planets. In addition, lightning is a conspicuous indicator of atmospheric activity whose potential is just beginning to be recognized and utilized. On more prosaic grounds, lightning observations are important for protection of life, property and services.

Analysis and Modeling of Intense Oceanic Lightning

NASA Astrophysics Data System (ADS)

Zoghzoghy, F. G.; Cohen, M.; Said, R.; Lehtinen, N. G.; Inan, U.

2014-12-01

Recent studies using lightning data from geo-location networks such as GLD360 suggest that lightning strokes are more intense over the ocean than over land, even though they are less common [Said et al. 2013]. We present an investigation of the physical differences between oceanic and land lightning. We have deployed a sensitive Low Frequency (1 MHz sampling rate) radio receiver system aboard the NOAA Ronald W. Brown research vessel and have collected thousands of lightning waveforms close to deep oceanic lightning. We analyze the captured waveforms, describe our modeling efforts, and summarize our findings. We model the ground wave (gw) portion of the lightning sferics using a numerical method built on top of the Stanford Full Wave Method (FWM) [Lehtinen and Inan 2008]. The gwFWM technique accounts for propagation over a curved Earth with finite conductivity, and is used to simulate an arbitrary current profile along the lightning channel. We conduct a sensitivity analysis and study the current profiles for land and for oceanic lightning. We find that the effect of ground conductivity is minimal, and that stronger oceanic radio intensity does not result from shorter current rise-time or from faster return stroke propagation speed.

Source Region Identification for Low Latitude Whistlers (L=1.08)

NASA Astrophysics Data System (ADS)

Gokani, S. A.; Singh, R.; Maurya, A. K.; Bhaskara, V.; Cohen, M.; Kumar, S.; Lichtenberger, J.

2014-12-01

Though whistlers are known and studied from past one century, the scientific community still strives to understand the generation and propagation mechanism of whistlers in very low latitude region. One of the solutions comes from locating the causative lightning discharges and source region of low latitude whistlers. In the present study, ~ 2000 whistlers recorded during period of one year (Dec, 2010 to Jan, 2011) at Allahabad (Geomag. lat. 16.79o N; L=1.08), India are correlated with lightning activity detected by World Wide Lightning Location Network (WWLLN) at and around conjugate region. About 63% of whistlers are correlated with the lightning strikes around conjugate region. Further to confirm this correlation, arrival azimuths of causative sferics are determined and the obtained azimuths points towards conjugate region of Allahabad. The characteristics of thunder cloud generating these whistlers are examined and found that the clouds with South-East alignment are more prone to trigger whistler waves. The seasonal and diurnal variation of whistler parameters such as occurrence rate, power spectral density and dispersion are also studied and explained on the basis of ionospheric conditions in low latitudes. The results obtained open a new window to look for the propagation mechanism of low latitude whistlers.

Full-wave reflection of lightning long-wave radio pulses from the ionospheric D region: Comparison with midday observations of broadband lightning signals

NASA Astrophysics Data System (ADS)

Jacobson, Abram R.; Shao, Xuan-Min; Holzworth, Robert

2010-05-01

We are developing and testing a steep-incidence D region sounding method for inferring profile information, principally regarding electron density. The method uses lightning emissions (in the band 5-500 kHz) as the probe signal. The data are interpreted by comparison against a newly developed single-reflection model of the radio wave's encounter with the lower ionosphere. The ultimate application of the method will be to study transient, localized disturbances of the nocturnal D region, including those instigated by lightning itself. Prior to applying the method to study lightning-induced perturbations of the nighttime D region, we have performed a validation test against more stable and predictable daytime observations, where the profile of electron density is largely determined by direct solar X-ray illumination. This article reports on the validation test. Predictions from our recently developed full-wave ionospheric-reflection model are compared to statistical summaries of daytime lightning radiated waveforms, recorded by the Los Alamos Sferic Array. The comparison is used to retrieve best fit parameters for an exponential profile of electron density in the ionospheric D region. The optimum parameter values are compared to those found elsewhere using a narrowband beacon technique, which used totally different measurements, ranges, and modeling approaches from those of the work reported here.

Total Lightning and Radar Storm Characteristics Associated with Severe Storms in Central Florida

NASA Technical Reports Server (NTRS)

Goodman, Steven J.; Raghavan, Ravi; Ramachandran, Rahul; Buechler, Dennis; Hodanish, Stephen; Sharp, David; Williams, Earle; Boldi, Bob; Matlin, Anne; Weber, Mark

1998-01-01

A number of prior studies have examined the association of lightning activity with the occurrence of severe weather and tornadoes, in particular. High flash rates are often observed in tornadic storms (Taylor, 1973; Johnson, 1980; Goodman and Knupp, 1993) but not always. Taylor found that 23% of nontornadic storms and 1% of non-severe storms had sferics rates comparable to the tornadic storms. MacGorman (1993) found that storms with mesocyclones produced more frequent intracloud (IC) lightning than cloud-to-ground (CG) lightning. MacGorman (1993) and others suggest that the lightning activity accompanying tomadic storms will be dominated by intracloud lightning-with an increase in intracloud and total flash rates as the updraft increases in depth, size, and velocity. In a recent study, Perez et al. (1998) found that CG flash rates alone are too variable to be a useful predictor of (F4, F5) tornado formation. Studies of non-tomadic storms have also shown that total lightning flash rates track the updraft, with rates increasing as the updraft intensities and decreasing rapidly with cessation of vertical growth or downburst onset (Goodman et al., 1988; Williams et al., 1989). Such relationships result from the development of mixed phase precipitation and increased hydrometer collisions that lead to the efficient separation of charge. Correlations between updraft strength and other variables such as cloud-top height, cloud water mass, and hail size have also been observed.

Estimating the D-Region Ionospheric Electron Density Profile Using VLF Narrowband Transmitters

NASA Astrophysics Data System (ADS)

Gross, N. C.; Cohen, M.

2016-12-01

The D-region ionospheric electron density profile plays an important role in many applications, including long-range and transionospheric communications, and coupling between the lower atmosphere and the upper ionosphere occurs, and estimation of very low frequency (VLF) wave propagation within the earth-ionosphere waveguide. However, measuring the D-region ionospheric density profile has been a challenge. The D-region is about 60 to 90 [km] in altitude, which is higher than planes and balloons can fly but lower than satellites can orbit. Researchers have previously used VLF remote sensing techniques, from either narrowband transmitters or sferics, to estimate the density profile, but these estimations are typically during a short time frame and over a single propagation path.We report on an effort to construct estimates of the D-region ionospheric electron density profile over multiple narrowband transmission paths for long periods of time. Measurements from multiple transmitters at multiple receivers are analyzed concurrently to minimize false solutions and improve accuracy. Likewise, time averaging is used to remove short transient noise at the receivers. The cornerstone of the algorithm is an artificial neural network (ANN), where input values are the received amplitude and phase for the narrowband transmitters and the outputs are the commonly known h' and beta two parameter exponential electron density profile. Training data for the ANN is generated using the Navy's Long-Wavelength Propagation Capability (LWPC) model. Results show the algorithm performs well under smooth ionospheric conditions and when proper geometries for the transmitters and receivers are used.

The First Fermi-GBM Terrestrial Gamma Ray Flash Catalog

NASA Astrophysics Data System (ADS)

Roberts, O. J.; Fitzpatrick, G.; Stanbro, M.; McBreen, S.; Briggs, M. S.; Holzworth, R. H.; Grove, J. E.; Chekhtman, A.; Cramer, E. S.; Mailyan, B. G.

2018-05-01

We present the first Fermi Space Telescope Gamma Ray Burst Monitor (GBM) catalog of 4,144 terrestrial gamma ray flashes (TGFs), detected since launch in 11 July 2008 through 31 July 2016. We discuss the updates and improvements to the triggered data and off-line search algorithms, comparing this improved detection rate of ˜800 TGFs per year with event rates from previously published TGF catalogs from other missions. A Bayesian block algorithm calculated the temporal and spectral properties of the TGFs, revealing a delay between the hard (>300 keV) and soft (≤300 keV) photons of around 27 μs. Detector count rates of "low-fluence" events were found to have average rates exceeding 150 kHz. Searching the World-Wide Lightning Location Network data for radio sferics within ±5 min of each TGF revealed a clean sample of 1,314 World-Wide Lightning Location Network locations, which were used to to accurately locate TGF-producing storms. It also revealed lightning and storm activity for specific regions, as well as seasonal and daily variations of global lightning patterns. Correcting for the orbit of Fermi, we quantitatively find a marginal excess of TGFs being produced from storms over land near oceans (i.e., narrow isthmuses and small islands). No difference was observed between the duration of TGFs over the ocean and land. The distribution of TGFs at a given local solar time for predefined American, Asian, and African regions were confirmed to correlate well with known regional lightning rates.

A de-noising algorithm based on wavelet threshold-exponential adaptive window width-fitting for ground electrical source airborne transient electromagnetic signal

NASA Astrophysics Data System (ADS)

Ji, Yanju; Li, Dongsheng; Yu, Mingmei; Wang, Yuan; Wu, Qiong; Lin, Jun

2016-05-01

The ground electrical source airborne transient electromagnetic system (GREATEM) on an unmanned aircraft enjoys considerable prospecting depth, lateral resolution and detection efficiency, etc. In recent years it has become an important technical means of rapid resources exploration. However, GREATEM data are extremely vulnerable to stationary white noise and non-stationary electromagnetic noise (sferics noise, aircraft engine noise and other human electromagnetic noises). These noises will cause degradation of the imaging quality for data interpretation. Based on the characteristics of the GREATEM data and major noises, we propose a de-noising algorithm utilizing wavelet threshold method and exponential adaptive window width-fitting. Firstly, the white noise is filtered in the measured data using the wavelet threshold method. Then, the data are segmented using data window whose step length is even logarithmic intervals. The data polluted by electromagnetic noise are identified within each window based on the discriminating principle of energy detection, and the attenuation characteristics of the data slope are extracted. Eventually, an exponential fitting algorithm is adopted to fit the attenuation curve of each window, and the data polluted by non-stationary electromagnetic noise are replaced with their fitting results. Thus the non-stationary electromagnetic noise can be effectively removed. The proposed algorithm is verified by the synthetic and real GREATEM signals. The results show that in GREATEM signal, stationary white noise and non-stationary electromagnetic noise can be effectively filtered using the wavelet threshold-exponential adaptive window width-fitting algorithm, which enhances the imaging quality.

Very low frequency (VLF) waves as diagnostic tool in remote sensing of D-region Ionosphere

NASA Astrophysics Data System (ADS)

Singh, Ashok; Verma, Uday Prakash

Large currents along the magnetic field transmit stresses between ionosphere and magnetosphere. If the electrons carrying such currents have high enough drift velocity, waves are generated. A wave is a disturbance that propagates through space and time, usually with transference of energy. Waves play major part in the Earth’s ionospheric dynamics. Since both the Earth and the ionosphere are good reflectors at very low frequencies (3 kHz 30 kHz), the lightning radiated impulses commonly known as radio atmospheric or sferics or tweeks travel thousands of kilometers in the Earth Ionosphere Wave Guide (EIWG) with low attenuation of ~ 2-3 dB/1000km. Since vlf waves are reflected by ionosphere, they can be used as potential tool to study the D-region ionosphere which plays a key role in the radio wave propagation. Since the year 2010, vlf waves are continuously being recorded at low latitude ground based Indian station Lucknow (Geomag. Lat. 17.60 N; Geomag. Long. 154.50 E) using Automatic Whistler Detector (AWD). More than 100 tweeks of multimode harmonics (n ≥ 3) observed during the year 2010-2011 are analyzed. Using these multimode tweeks as remote sensing tool to explore D-region ionosphere we have estimated various medium parameters such as electron density, ionospheric reflection height and the propagation distance etc. Electron density in the D-region ionosphere varies from 40-160 cm-3 for various modes, ionospheric reflection height varies in the range 70 - 85 km, and the propagation distance was found to vary from 2 km - 6 km in the waveguide to the receiving site.

Triangulations of sprites relative to parent lighting near the Oklahoma Lightning Mapping Array

NASA Astrophysics Data System (ADS)

Lu, G.; Cummer, S. A.; Li, J.; Lyons, W. A.; Stanley, M. A.; Krehbiel, P. R.; Rison, W.; Thomas, R. J.; Weiss, S. A.; Beasley, W. H.; Bruning, E. C.; MacGorman, D. R.; Palivec, K.; Samaras, T. M.

2012-12-01

Temporal and spatial development of sprite-producing lightning flashes is examined with coordinated observations over an asymmetric mesoscale convective system on June 29, 2011 near the Oklahoma Lightning Mapping Array (OK-LMA). About 30 sprites were mutually observed from Bennett, Colorado and Hawley, Texas, allowing us to triangulate sprite formation in comparison with spatial/temporal development of the parent lightning. Complementary measurements of broadband (<1 Hz to ~300 kHz) radio frequency lightning signals are available from several magnetic sensors across the United States. Our analyses indicate that although sprite locations can be significantly offset horizontally (up to 70 km) from the parent ground stroke, they are usually laterally within 30 km of the in-cloud lightning activity during the 100 ms time interval prior to the sprite production. This is true for short-delayed sprites produced within 20 ms after a causative stroke, and long-delayed sprites appearing up to more than 200 ms after the stroke. Multiple sprites appearing as dancing/jumping events can be produced during one single flash either in a single lightning channel, through series of current surges superposed on a long and intense continuing current, or in multiple lightning channels through distinct ground strokes of the flash. The burst of continuous very-low-frequency/low-frequency lightning sferics commonly observed in association with sprites is linked to the horizontal progression of multiple negative leaders through positive charged regions of the cloud, which are typically centered at altitudes ~1-2 km (or more) above the freezing level.

Lunar biological effects and the magnetosphere.

PubMed

Bevington, Michael

2015-12-01

The debate about how far the Moon causes biological effects has continued for two millennia. Pliny the Elder argued for lunar power "penetrating all things", including plants, fish, animals and humans. He also linked the Moon with tides, confirmed mathematically by Newton. A review of modern studies of biological effects, especially from plants and animals, confirms the pervasive nature of this lunar force. However calculations from physics and other arguments refute the supposed mechanisms of gravity and light. Recent space exploration allows a new approach with evidence of electromagnetic fields associated with the Earth's magnetotail at full moon during the night, and similar, but more limited, effects from the Moon's wake on the magnetosphere at new moon during the day. The disturbance of the magnetotail is perhaps shown by measurements of electric fields of up to 16V/m compared with the usual <1V/m, suggesting the possibility of weak biological effects on some sensitive organisms. Similar intensities found in sferics, geomagnetic storms, aurora disturbance, sensations of a 'presence' and pre-seismic electromagnetic radiation are known to affect animals and 10-20% of the human population. There is now evidence for mechanisms such as calcium flux, melatonin disruption, magnetite and cryptochromes. Both environmental and receptor variations explain confounding factors and inconsistencies in the evidence. Electromagnetic effects might also account for some evolutionary changes. Further research on lunar biological effects, such as acute myocardial infarction, could help the development of strategies to reduce adverse effects for people sensitive to geomagnetic disturbance. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

Fast Positive Breakdown, NBEs, and Lightning Initiation

NASA Astrophysics Data System (ADS)

Krehbiel, P. R.; Rison, W.; Stock, M.; Edens, H. E.; Shao, X. M.; Thomas, R. J.; Stanley, M. A.; Zhang, Y.

2016-12-01

High power narrrow bipolar events (NBEs) have been found to be produced by arelatively unknown type of discharge, called fast positive breakdown (Rison etal., 2016). The breakdown occurs with a wide range of strengths, both in terms of its broadband sferic and its VHF radiation, and is found to be theinitiating event of many and likely all lightning discharges inside storms. Itdoes not produce a conducting channel but instead appears to be produced by avolumetric system of repeated, cascading positive streamers in virgin air.That positive corona and streamers would be responsible for initiatinglightning was proposed in the 1960s by Loeb, Dawson and Winn. In the 1970sPhelps and Griffiths showed that the streamers would be self-intensifying,leading to negative breakdown being initiated back at their starting points.Petersen et al. (2008) described experimental results showing that thestreamers could be initiated by ice crystals at cold temperatures, and thephysical processes leading to the breakdown being fast has been reported inrecent modeling studies by Shi et al. (2016). In this paper we summarize the observational data in support of the abovefindings, and report on additional observations of NBEs and lightninginitiation currently being obtained at Kennedy Space Center, Florida. References: Rison W., P.R. Krehbiel M.G.Stock, H.E. Edens, X-M. Shao, R.J. Thomas,M.A. Stanley, Y. Zhang, Observations of narrow bipolar events revealhow lightning is initiated in thunderstorms, Nature Comms. 7, 2016.doi:10.1038/ncomms10721. Petersen, D., Bailey, M., Beasley, W. & Hallett, J. A brief review ofthe problem of lightning initiation and a hypothesis of initiallightning leader formation. J. Geophys. Res. 113, D17205 (2008). Shi, F., N. Liu, and H. K. Rassoul (2016), Properties of relativelylong streamers initiated from an isolated hydrometeor, J. Geophys.Res. Atmos., 121, 7284-7295, doi:10.1002/2015JD024580.

Joint 3D Inversion of ZTEM Airborne and Ground MT Data with Application to Geothermal Exploration

NASA Astrophysics Data System (ADS)

Wannamaker, P. E.; Maris, V.; Kordy, M. A.

2017-12-01

ZTEM is an airborne electromagnetic (EM) geophysical technique developed by Geotech Inc® where naturally propagated EM fields originating with regional and global lightning discharges (sferics) are measured as a means of inferring subsurface electrical resistivity structure. A helicopter-borne coil platform (bird) measuring the vertical component of magnetic (H) field variations along a flown profile is referenced to a pair of horizontal coils at a fixed location on the ground in order to estimate a tensor H-field transfer function. The ZTEM method is distinct from the traditional magnetotelluric (MT) method in that the electric (E) fields are not considered because of the technological challenge of measuring E-fields in the dielectric air medium. This can lend some non-uniqueness to ZTEM interpretation because a range of conductivity structures in the earth depending upon an assumed background earth resistivity model can fit ZTEM data to within tolerance. MT data do not suffer this particular problem, but they are cumbersome to acquire in their common need for land-based transport often in near-roadless areas and for laying out and digging the electrodes and H coils. The complementary nature of ZTEM and MT logistics and resolution has motivated development of schemes to acquire appropriate amounts of each data type in a single survey and to produce an earth image through joint inversion. In particular, consideration is given to surveys where only sparse MT soundings are needed to drastically reduce the non-uniqueness associated with background uncertainty while straining logistics minimally. Synthetic and field data are analysed using 2D and 3D finite element platforms developed for this purpose. Results to date suggest that indeed dense ZTEM surveys can provide detailed heterogeneous model images with large-scale averages constrained by a modest number of MT soundings. Further research is needed in determining the allowable degree of MT sparseness and the relative weighting of the two data sets in joint inversion.

Estimating Parameters for the Earth-Ionosphere Waveguide Using VLF Narrowband Transmitters

NASA Astrophysics Data System (ADS)

Gross, N. C.; Cohen, M.

2017-12-01

Estimating the D-region (60 to 90 km altitude) ionospheric electron density profile has always been a challenge. The D-region's altitude is too high for aircraft and balloons to reach but is too low for satellites to orbit at. Sounding rocket measurements have been a useful tool for directly measuring the ionosphere, however, these types of measurements are infrequent and costly. A more sustainable type of measurement, for characterizing the D-region, is remote sensing with very low frequency (VLF) waves. Both the lower ionosphere and Earth's ground strongly reflect VLF waves. These two spherical reflectors form what is known as the Earth-ionosphere waveguide. As VLF waves propagate within the waveguide, they interact with the D-region ionosphere, causing amplitude and phase changes that are polarization dependent. These changes can be monitored with a spatially distributed array of receivers and D-region properties can be inferred from these measurements. Researchers have previously used VLF remote sensing techniques, from either narrowband transmitters or sferics, to estimate the density profile, but these estimations are typically during a short time frame and over a narrow propagation region. We report on an effort to improve the understanding of VLF wave propagation by estimating the commonly known h' and beta two parameter exponential electron density profile. Measurements from multiple narrowband transmitters at multiple receivers are taken, concurrently, and input into an algorithm. The cornerstone of the algorithm is an artificial neural network (ANN), where input values are the received narrowband amplitude and phase and the outputs are the estimated h' and beta parameters. Training data for the ANN is generated using the Navy's Long-Wavelength Propagation Capability (LWPC) model. Emphasis is placed on profiling the daytime ionosphere, which has a more stable and predictable profile than the nighttime. Daytime ionospheric disturbances, from high solar activity, are also analyzed.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Henderson, Bradley G; Suszcynsky, David M; Hamlin, Timothy E

Los Alamos National Laboratory (LANL) owns and operates an array of Very-Low Frequency (VLF) sensors that measure the Radio-Frequency (RF) waveforms emitted by Cloud-to-Ground (CG) and InCloud (IC) lightning. This array, the Los Alamos Sferic Array (LASA), has approximately 15 sensors concentrated in the Great Plains and Florida, which detect electric field changes in a bandwidth from 200 Hz to 500 kHz (Smith et al., 2002). Recently, LANL has begun development of a new dual-band RF sensor array that includes the Very-High Frequency (VHF) band as well as the VLF. Whereas VLF lightning emissions can be used to deduce physicalmore » parameters such as lightning type and peak current, VHF emissions can be used to perform precise 3d mapping of individual radiation sources, which can number in the thousands for a typical CG flash. These new dual-band sensors will be used to monitor lightning activity in hurricanes in an effort to better predict intensification cycles. Although the new LANL dual-band array is not yet operational, we have begun initial work utilizing both VLF and VHF lightning data to monitor hurricane evolution. In this paper, we present the temporal evolution of Rita's landfall using VLF and VHF lightning data, and also WSR-88D radar. At landfall, Rita's northern eyewall experienced strong updrafts and significant lightning activity that appear to mark a transition between oceanic hurricane dynamics and continental thunderstorm dynamics. In section 2, we give a brief overview of Hurricane Rita, including its development as a hurricane and its lightning history. In the following section, we present WSR-88D data of Rita's landfall, including reflectivity images and temporal variation. In section 4, we present both VHF and VLF lightning data, overplotted on radar reflectivity images. Finally, we discuss our observations, including a comparison to previous studies and a brief conclusion.« less

Positron Annihilation in Thunderstorms Observed by ILDAS.

NASA Astrophysics Data System (ADS)

Kochkin, P.; Sarria, D., Sr.; Van Deursen, A.; de Boer, A.; Bardet, M.; Allasia, C.; Flourens, F.; Østgaard, N.

2017-12-01

Positron clouds within thunderstorms were for the first time reported in 2015 [Dwyer et al. 2015]. The observation was made by the Airborne Detector for Energetic Lightning Emissions (ADELE) in 2009 at 14.1 km altitude. Strong 511 keV line enhancement was recorded synchronously with nearby electrical activity. It lasted at least 0.2 s and was modeled as annihilation from disperse positron cloud more than a kilometer across. Different positron generation mechanisms were proposed in the paper. In January 2016 an Airbus A340 factory test aircraft was intentionally flying through thunderstorms over Northern Australia. The aircraft was equipped with a dedicated in-flight lightning detection system ILDAS (http://ildas.nlr.nl). The system contains two gamma-ray scintillation detectors each with 38x38 mm cylinder LaBr3 crystals. Total 9 video cameras were installed on-board to monitor the outer surfaces. When the aircraft flew at 12 km inside an active thundercloud, the ambient electric field was strong enough to trigger electrical discharges from the sharp edges. One sequence of such discharges was accompanied with enhancements of 511 keV line, each lasted for 0.5 - 1.0 s and total duration over 15 s. The video cameras recorded electrical discharges attached to the aircraft during this process. ILDAS reported brief 100 A current pulses in association with these discharges. Ground-based lightning location networks, i.e. WWLLN and local Australian LIAS, have not detected any sferics from this region. A detailed Geant4 model of the aircraft was created. The model was used to test different production mechanisms for the observed emission. In this presentation we will show a detailed reconstruction ofthe events with precise mapping on infrared cloud snapshot. Videos from the cameras at the positron detection moment will be shown. The results of the Geant4 simulation will be presented and discussed. References: 1. Dwyer, Joseph R., et al. "Positron clouds within thunderstorms." Journal of Plasma Physics 81.4 (2015).

Measurement of electromagnetic waves in ELF and VLF bands to monitor lightning activity in the Maritime Continent

NASA Astrophysics Data System (ADS)

Yamashita, Kozo; Takahashi, Yukihiro; Ohya, Hiroyo; Tsuchiya, Fuminori; Sato, Mitsuteru; Matsumoto, Jun

2013-04-01

Data of lightning discharge has been focused on as an effective way for monitoring and nowcasting of thunderstorm activity which causes extreme weather. Spatial distribution of lightning discharge has been used as a proxy of the presence or absence of deep convection. Latest observation shows that there is extremely huge lightning whose scale is more than hundreds times bigger than that of averaged event. This result indicates that lightning observation should be carried out to estimate not only existence but also scale for quantitative evaluation of atmospheric convection. In this study, lightning observation network in the Maritime Continent is introduced. This network is consisted of the sensors which make possible to measure electromagnetic wave radiated from lightning discharges. Observation frequency is 0.1 - 40 kHz for the measurement of magnetic field and 1 - 40 kHz for that of electric field. Sampling frequency is 100 kHz. Waveform of electromagnetic wave is recorded by personal computer. We have already constructed observation stations at Tainan in Taiwan (23.1N, 121.1E), Saraburi in Thailand (14.5N, 101.0E), and Pontianak in Indonesia (0.0N, 109.4E). Furthermore, we plan to install the monitoring system at Los Banos in Philippines (14.18, 121.25E) and Hanoi in Viet Nam. Data obtained by multipoint observation is synchronized by GPS receiver installed at each station. By using data obtained by this network, location and scale of lightning discharge can be estimated. Location of lightning is determined based on time of arrival method. Accuracy of geolocation could be less than 10km. Furthermore, charge moment is evaluated as a scale of each lightning discharge. It is calculated from electromagnetic waveform in ELF range (3-30 kHz). At the presentation, we will show the initial result about geolocation for source of electromagnetic wave and derivation of charge moment value based on the measurement of ELF and VLF sferics.

Initial Results of DC Electric Fields, Associated Plasma Drifts, Magnetic Fields, and Plasma Waves Observed on the C/NOFS Satellite

NASA Technical Reports Server (NTRS)

Pfaff, R.; Freudenreich, H.; Bromund, K.; Klenzing, J.; Rowland, D.; Maynard, N.

2010-01-01

Initial results are presented from the Vector Electric Field Investigation (VEFI) on the Air Force Communication/Navigation Outage Forecasting System (C/NOFS) satellite, a mission designed to understand, model, and forecast the presence of equatorial ionospheric irregularities. The VEFI instrument includes a vector DC electric field detector, a fixed-bias Langmuir probe operating in the ion saturation regime, a flux gate magnetometer, an optical lightning detector, and associated electronics including a burst memory. Compared to data obtained during more active solar conditions, the ambient DC electric fields and their associated E x B drifts are variable and somewhat weak, typically < 1 mV/m. Although average drift directions show similarities to those previously reported, eastward/outward during day and westward/downward at night, this pattern varies significantly with longitude and is not always present. Daytime vertical drifts near the magnetic equator are largest after sunrise, with smaller average velocities after noon. Little or no pre-reversal enhancement in the vertical drift near sunset is observed, attributable to the solar minimum conditions creating a much reduced neutral dynamo at the satellite altitude. The nighttime ionosphere is characterized by larger amplitude, structured electric fields, even where the plasma density appears nearly quiescent. Data from successive orbits reveal that the vertical drifts and plasma density are both clearly organized with longitude. The spread-F density depletions and corresponding electric fields that have been detected thus far have displayed a preponderance to appear between midnight and dawn. Associated with the narrow plasma depletions that are detected are broad spectra of electric field and plasma density irregularities for which a full vector set of measurements is available for detailed study. Finally, the data set includes a wide range of ELF/VLF/HF oscillations corresponding to a variety of plasma waves, in particular banded ELF hiss, whistlers, and lower hybrid wave turbulence triggered by lightning-induced sferics. The VEFI data represents a new set of measurements that are germane to numerous fundamental aspects of the electrodynamics and irregularities inherent to the Earth's low latitude ionosphere.

Observations of Sprites above Haiti/Dominican Republic Thunderstorms from Arecibo Observatory, Puerto Rico

NASA Astrophysics Data System (ADS)

Pasko, V. P.; Stanley, M.; Mathews, J. D.; Inan, U. S.; Wood, T. G.; Cummer, S. A.; Williams, E. R.; Heavner, M. J.

2002-12-01

In August-September 2001 an experimental campaign has been conducted in Puerto Rico to perform correlative studies of lightning and lightning-induced ionospheric effects. The campaign, which was sponsored by a Small Grant for Exploratory Research from the National Science Foundation to Penn State University, had a broad range of scientific goals including studies ionospheric effects of thunderstorms, studies of VHF-quiet positive leaders and studies of large scale optical phenomena above ocean thunderstorms in tropics. As part of this program we conducted night time video recordings of lightning and large scale luminous phenomena above thunderstorms using a SONY DCR TRV 730 CCD video camera equipped with a blue extended ITT Night Vision GEN III NQ 6010 intensifier with 40 deg field of view. The intensifier provided a monochrome (predominantly green) image output. The video system was deployed at the Lidar Laboratory on the grounds of Arecibo Observatory, Puerto Rico (18.247 deg N, 66.754 deg W, elevation 305 m above the sea level). In this talk we report results of observations conducted between 01 and 03 UT on September 3, 2001. A total of 7 sprite events have been detected above a large thunderstorm system (cloud area exceeding 104 km2) located approximately 500 km from the observational site above Haiti/Dominican Republic. The observed events exhibited typical sprite features documented in other parts of the globe, including single columns, groups of columns, relatively small horizontal glows confined to higher altitudes, as well as two large and impulsive events with the transverse extent ~eq50 km. In this talk we will also report results of preliminary analysis of available ELF electromagnetic signatures associated with the observed events recorded by Stanford University at Palmer Station, Antarctica, Duke University, MIT and Los Alamos Sferic Array in Florida. Acknowledgments: The GEN III intensifier has been provided by ITT Night Vision Industries. We are grateful to M. Robinson of ITT Industries for support of our program. We thank W. Lyons for useful discussions. We are indebted to S. Gonzalez, Q. Zhou, M. Sulzer, C. Tepley, J. Friedman, E. Robles, A. Venkataraman and E. Castro for support of our observations at Arecibo Observatory.

Initial Results from the Vector Electric Field Investigation on the C/NOFS Satellite

NASA Technical Reports Server (NTRS)

Pfaff, R.; Rowland, D.; Acuna, M.; Le, G.; Farrell, W.; Holzworth, R.; Wilson, G.; Burke, W.; Freudenreich, H.; Bromund, K.;

TLE Balloon experiment campaign carried out on 25 August 2006 in Japan

NASA Astrophysics Data System (ADS)

Takahashi, Y.; Chikada, S.; Yoshida, A.; Adachi, T.; Sakanoi, T.

2006-12-01

The balloon observation campaign for TLE and lightning study was carried out 25 August 2006 in Japan by Tohoku University, supported by JAXA. The balloon was successfully launched at 18:33 LT at Sanriku Balloon Center of JAXA located in the east coast of northern part of Japan (Iwate prefecture). Three types of scientific payloads were installed at the 1 m-cubic gondola, that is, 3-axis VLF electric filed antenna and receiver (VLFR), 4 video frame CCD cameras (CCDI) and 2-color photometer (PM). The video images were stored in 4 HD video recorders, which have 20GB memories respectively, at 30 frames/sec and VLFR and PM data were put into digital data recorder with 30 GB memory at sampling rate of 100 kHz. The balloon floated at the altitude of 13 km until about 20:30 LT, going eastward and went up to 26 km at a distance of 130 km from the coast. And it went back westward at the altitude of 26 km until midnight. The total observation period is about 5 hours. Most of the equipments worked properly except for one video recorder. Some thunderstorms existed within the direct FOV from the balloon in the range of 400-600 km and more than about 400 lightning flashes were recorded as video images. We confirmed that, at least, one sprite halo was captured by CCDI which occurred in the oceanic thunderstorm at a distance of about 500 km from balloon. This is the first TLE image obtained by a balloon-borne camera. Simultaneous measurements of VLF sferics and lightning/TLE images will clarify the role of intracloud (IC) currents in producing and/or modulating TLEs as well as cloud-to-ground discharges (CG). Especially the effect of horizontal components will be investigated in detail, which cannot be detected on the ground, to explain the unsolved properties of TLEs, such as long time delay of TLE from the timing of stroke and large horizontal displacement between CG and TLEs.

Lightning-driven electric and magnetic fields measured in the stratosphere: Implications for sprites

NASA Astrophysics Data System (ADS)

Thomas, Jeremy Norman

A well accepted model for sprite production involves quasi-electrostatic fields (QSF) driven by large positive cloud-to-ground (+CG) strokes that can cause electrical breakdown in the middle atmosphere. A new high voltage, high impedance, double Langmuir probe instrument is designed specifically for measuring these large lightning-driven electric field changes at altitudes above 30 km. This High Voltage (HV) Electric Field Detector measured 200 nearby (<75 km) lightning-driven electric field changes, up to 140 V/m in magnitude, during the Brazil Sprite Balloon Campaign 2002--03. A numerical QSF model is developed and compared to the in situ measurements. It is found that the amplitudes and relaxation times of the electric fields driven by these nearby lightning events generally agree with the numerical QSF model, which suggests that the QSF approach is valid for modeling lightning-driven fields. Using the best fit parameters of this comparison, it is predicted that the electric fields at sprite altitudes (60--90 km) never surpass conventional breakdown in the mesosphere for each of these 200 nearby lightning events. Lightning-driven ELF to VLF (25 Hz--8 kHz) electric field changes were measured for each of the 2467 cloud-to-ground lightning (CGs) detected by the Brazilian Integrated Lightning Network (BIN) at distances of 75--600 km, and magnetic field changes (300 Hz--8 kHz) above the background noise were measured for about 35% (858) of these CGs. ELF pulses that occur 4--12 ms after the retarded time of the lightning sferic, which have been previously attributed to sprites, were found for 1.4% of 934 CGs examined with a strong bias towards +CGs (4.9% or 9/184) compared to -CGs (0.5% or 4/750). These results disagree with results from the Sprites99 Balloon Campaign [Bering et al., 2004b], in which the lightning-driven electric and magnetic field changes were rare, while the CG delayed ELF pulses were frequent. The Brazil Campaign results thus suggest that mesospheric currents are likely the result of the QSF driven by large charge moment strokes, which are usually +CG strokes, initiating breakdown in the middle atmosphere.

Thunderstorm monitoring with VLF network and super dense meteorological observation system

NASA Astrophysics Data System (ADS)

Takahashi, Yukihiro; Sato, Mitsuteru

2015-04-01

It's not easy to understand the inside structure and developing process of thunderstorm only with existing meteorological instruments since its horizontal extent of the storm cell is sometimes smaller than an order of 10 km while one of the densest ground network in Japan, AMEDAS, consists of sites located every 17 km in average and the resolution of meteorological radar is 1-2 km in general. Even the X-band radar realizes the resolution of 250 m or larger. Here we suggest a thunderstorm monitoring system consisting of the network of VLF radio wave receivers and the super dense meteorological observation system with simple and low cost plate-type sensors that can be used for measurement both of raindrop and vertical electric field change caused by cloud-to-ground lightning discharge, adding to basic equipments for meteorological measurements. The plate-type sensor consists of two aluminum plates with a diameter of 10-20 cm. We carried out an observation campaign in summer of 2013 in the foothills of Mt. Yastugatake, Yamanashi and Nagano prefectures in Japan, installing 6 plate-type sensors at a distance of about 4 km. Horizontal location, height and charge amount of each lightning discharge are estimated successfully based on the information of electric field changes at several observing sites. Moreover, it was found that the thunderstorm has a very narrow structure smaller than 300 m that cannot be measured by any other ways, counting the positive and negative pulses caused by attachment of raindrop to the sensor plate, respectively. We plan to construct a new super dense observation network in the north Kanto region, Japan, where the lightning activity is most prominent in summer Japan and surrounded by our VLF systems developed for detecting sferics from lightning discharge, distributing more than several tens of sensors at every 4 km or shorter, such as an order of 100 m at minimum. This kind of new type network will reveal the unknown fine structures of thunderstorms and open the door for constructing real time alert system of torrential rainfall and lightning stroke especially in the city area.

Broadband VHF Interferometer Observations of an Energetic In-cloud Pulse (EIP)

NASA Astrophysics Data System (ADS)

Tilles, J.; Krehbiel, P. R.; Stanley, M. A.; Rison, W.; Lyu, F.; Cummer, S.; Liu, N.; Dwyer, J. R.; Brown, R. G.; Wilson, J. G.

2017-12-01

Energetic in-cloud pulses (EIPs) are a little-known in-cloud subprocess of lightning. While they may be best identified by their large peak current (>200 kA) [Lyu et al., Geophys. Res. Lett., 42, 2015], they differ from narrow bipolar events (NBEs) - another type of in-cloud, high peak-current process - in that the sferic of an EIP lasts an order of magnitude longer ( ˜100 us) than that of a typical NBE ( ˜10 us). To further differentiate them from NBEs, EIPs are generally embedded within other electrical activity, whereas NBEs are known to primarily occur in isolation or as a lightning-initiating event [Smith et al., J. Geophys. Res., 104, D4, 4189-4212, 1999; Rison et al., Nat. Commun., 7, 10721, 2016]. Moreover, EIPs may have an intrinsic connection with the production of terrestrial gamma ray flashes (TGFs) [Cummer et al., Geophys. Res. Lett., 41, 8586-8593, 2014].Here we present coincident broadband VHF interferometer (INTF) observations and electric and magnetic field waveforms of an EIP with an associated NLDN peak current of 247 kA. The EIP occurs nearly 4 ms into a normal-polarity intracloud flash as part of the upward extension of the negative-polarity lightning leader. For this reason, we suspect that EIPs are a more energetic version of initial breakdown pulses (IBPs), which accompany the development of negative stepped leaders [e.g. Marshall et al., J. Geophys. Res. Atmos., 119, 445-460, 2014]. In addition, we show similarities with NBE-producing fast breakdown [Rison et al., 2016; Tilles et al., AE12A-03, AGU Fall Meeting, 2016], in that the breakdown accompanying the EIP propagates over a similar vertical extent ( ˜0.5-1 km) and with similar propagation speed ( ˜3×107 m/s). The INTF was developed by New Mexico Tech and has been deployed at Kennedy Space Center since July 2016. It employed three 100-m baselines in 2016, has a bandwidth of 14-88 MHz and samples at 180 MS/s with 16-bit resolution. A synchronously digitized fast antenna (FA), with 100-μ s decay time constant, samples the electric field, and the whole INTF+FA system is automatically triggered on strong VHF radiation. Coincident VLF/ LF (1-300 kHz, sampled at 1 MS/s) observations are made with Duke University's magnetic sensor network.

Observations of 50/60 Hz Power Line Radiation in the Low Latitude Ionosphere Detected by the Electric Field Instrument on the C/NOFS Satellite

NASA Astrophysics Data System (ADS)

Pfaff, R. F., Jr.; Freudenreich, H. T.; Simoes, F. A.; Liebrecht, M. C.; Farrell, W.

2017-12-01

One of the most ubiquitous forms of EM radiation emanating from the earth's surface is that of power line radiation. Associated with AC electric power generation, such emissions are typically launched along conducting power lines that may travel hundreds, or even thousands of km, from generating stations. The fundamental frequencies of such emissions are characteristically 50 Hz or 60 Hz, depending on the regional standards for power generation/consumption. The frequency of this radiation is well below that of the plasma frequency of the ionosphere (typically several MHz) and hence is expected to reflect back to the earth and propagate in the waveguide formed by the earth's surface and the bottom ledge of the ionosphere, typically near 100 km. Given that such power lines are widespread on the exposed lithosphere, the leakage of some ELF emissions associated with electric power generation might nevertheless be expected in the ionosphere, in the same manner in which a small fraction of the power associated with ELF Schumann resonances and lightning sferics have been shown to penetrate into the ionosphere. We present direct measurements of 50/60 Hz power line radiation detected by in situ probes on an orbiting satellite in the earth's ionosphere. The data were gathered by the Vector Electric Field Investigation (VEFI) tri-axial double probe detector flown on the Communication/Navigation Outage Forecast System (C/NOFS) satellite. C/NOFS was launched in April, 2008 into a low latitude (13 deg inclination) orbit with perigee and apogee of 400 km and 850 km, respectively. The electric field wave data were gathered by ELF receivers comprised of two orthogonal broadband channels sampled at 512 s/sec each, and digitized with 16 bit A/D converters. The data show distinct 60 Hz emissions while the satellite sampled within the Brazilian sector whereas distinct 50 Hz emissions were detected over India. Other, less distinct, emissions were observed over Africa and southeast Asia. We discuss the characteristics of the received emissions, including their amplitudes and spectral features (i.e., harmonics). We use these observations to advance our understanding of how natural terrestrial ELF emissions, such as those associated with Schumann resonances and lightning, penetrate into the ionosphere.

The D-Region Ionospheric Response to the 2017 Solar Eclipse

NASA Astrophysics Data System (ADS)

Cohen, M.; McCormick, J.; Gross, N. C.; Higginson-Rollins, M. A.

2017-12-01

VLF/LF radio remote sensing (0.5-500 kHz) is an effective means for quantifying the D-region ionosphere (60-90 km altitude). Disturbances in the ionospheric electron density induce changes in the propagation of VLF/LF signals, so a network of transmitters and receivers can effectively "image" a disturbed region. VLF/LF signals can all be detected from 100s-1000s of km away. We utilize Georgia Tech's network of highly-sensitive VLF/LF receivers to quantify the lower ionospheric response to the "Great American Eclipse". Nine of these were deployed and operational across the Continental US, Alaska and Puerto Rico all operated successfully. Each receiver synchronously recorded the full radio spectrum between 0.5-470 kHz. The included figure shows the eclipse track at 80 km altitude with a green swath. The nine operational receivers are shown with blue stars, and operational VLF/LF transmitters in dark red. Gray lines are shown for each great-circle path linking a VLF/LF transmitter to a receiver. This constellation forms a dense spider's-web grid of radio links, with which we can effectively image the disturbed patch of the D-region ionosphere as it moves across the country. In addition, shown in yellow are NDGPS transmitters which lie between 285-325 kHz. The red dots are the 230,000 geolocated lightning strokes during the 90-mintue eclipse pass, each of which emitted an intense VLF/LF impulse. These are also detected by our receivers. We present our observations and comparison with a theoretical model, using a combination of three techniques established by a series of three 2017 journal papers: (1) Polarization measurements of VLF/LF transmitter signals, (2) Lightning-generated VLF sferics detected 1000s of km away, and (3) NDGPS beacons near 300 kHz for shorter-range sounding of a small patch of the ionosphere. We find evidence of large scale ionospheric changes which affect the D-region over the entire continental region with a slowly-varying signal perturbation. At some sites close to the totality zone, however, we have evidence of forward scattering from the shadow of the moon, which effectively is a patch of nighttime surrounded by daytime, that can only be observed in a narrower region around the totality zone. Implications of these results for D-region ionospheric dynamics are discussed.

Ionosphere-magnetosphere studies using ground based VLF radio propagation technique: an Indian example

NASA Astrophysics Data System (ADS)

Chakravarty, Subhas

Since IGY period (1957-58), natural and artificially produced Very Low Frequency (VLF) elec-tromagnetic radiations are being recorded at large number of ground stations all over the world and on-board satellites to study various radio wave-thermal/energetic plasma interactive pro-cesses related to earth's ionosphere-plasmasphere-magnetosphere environment. The terrestrial propagation of these VLF radio waves are primarily enabled through the earth ionosphere wave guide (EIWG) mode to long horizontal distances around the globe and ducted along the ge-omagnetic field lines into the conjugate hemisphere through the plasmasphere-magnetosphere regions. The time frequency spectra of the received signals indicate presence of dispersion (wave/group velocities changing with frequency) and various cut-off frequencies based on the width of the EIWG, electron gyro and plasma frequencies etc., providing several types of received signals like whistlers, chorus, tweeks, hiss and hisslers which can be heard on loud-speakers/earphones with distinguishing audio structures. While the VLF technique has been a very effective tool for studying middle and high latitude phenomena, the importance of the similar and anomalous observations over the Indian low latitude stations provide potentially new challenges for their scientific interpretation and modelling. The ducted and non-ducted magnetospheric propagation, pro-longitudinal (PL) mode, low latitude TRIMPI/TLE (Tran-sient Luminous Emissions) or other effects of wave-particle/wave-wave interactions, effects due to ionospheric irregularities and electric fields, full wave solutions to D-region ionisation per-turbations due to solar and stellar energetic X-and γ ray emissions during normal and flaring conditions are a few problems which have been addressed in these low latitude studies over India. Since the conjugate points of Indian stations lie over the Indian oceanic region, the VLF propagation effects would be relatively free from sferics at least in some seasons providing a noise free environment for observing rare and new phenomena requiring better SNR to detect such changes, The VLF signals from the active seismic zones or other electro-geological sources would require high sensitivities of the system and suitable network of transmitting and receiv-ing stations designed for targeted data and applications. Some new results over Indian and other regions show evidences of earthquake related seismo-geological VLF emissions with the potential of being used as a prognostic tool, change in ozone and ion production in the night time middle atmosphere due to transit of stellar x-ray/γ ray sources. Results obtained on whistlers and related studies from a number of Indian stations covering geomagnetic latitude range between 13-24 N will be mentioned and reviewed in the background of theoretical understanding of the lightning return stroke signal elements, VLF propagation through cold plasma, ionospheric wave guide mode, electron precipitation due to cyclotron resonance and production of atomic oxygen O (3 P) and ionisation in the mesosphere due to solar/stellar UV/X/γrays. Use of future VLF techniques in terms of improving ground based observations, critical analysis of available satellite data in the context and real time moni-toring/modelling of earth's geosphere and space weather conditions will be considered for a possible programme of a developing country.