Lightning location with variable radio wave propagation velocity

Journal of Geophysical Research: Atmospheres, 2003

An experimental long‐range lightning detection system consisting of a network (ZEUS) of six ground‐based radio receivers has been deployed in Europe and has been operated since June 2001. The receivers detect and measure the electromagnetic signal emitted by a lightning source in the Very Low Frequency band, between 5 and 15 kHz (sferics), which propagates over thousands of kilometers in the Earth‐ionosphere waveguide. In this study, lightning location retrievals from the ZEUS network are compared against more definitive sources in order to investigate issues on long‐range lightning retrieval accuracy and detection efficiency. The validation study is carried out over three regions: the U.S. East Coast/Northwestern Atlantic, the African continent, and within the network (Spain). Data originate from the U.S. National Lightning Detection Network, the Lighting Imaging Sensor aboard the Tropical Rainfall Measurement Mission Satellite, and the Spanish National Lightning Network. We invest...

Journal of Geophysical Research, 1997

The mapping of lightning radiation sources produced by the operational Time-of-Arrival National Aeronautics and Space Administration/Lightning Detection and Ranging (NASA/LDAR) system is compared with that of the Interferometric French Office National D'Etudes et de Recherches Aerospatiales (ONERA-3D) system. The comparison comprises lightning activity in three Florida storms and also individual flashes in one of these storms. A•lthough limited in scope, the comparison and analysis show a significant difference in the representation of lightning radiation by each mapping system. During the duration of a flash, the LDAR data show a continuity in time and a three-dimensional structure of radiation sources. The ONERA-3D radiation source data are more intermittent in time and have a more twodimensional structure. The distinction between the radiation sources mapped by the two systems is also reflected in the difference between their propagation speeds, 10 4-10 5 rn s-1, estimated by the LDAR system, and 107-10 8 rn s-1, estimated by the ONERA-3D system. We infer that this difference occurs because most of the radiation sources mapped with LDAR are associated with virgin breakdown processes typical of slowly propagating negative leaders. On the other hand, most of the radiation sources mapped with ONERA-3D are produced by fast intermittent negative breakdown processes typical of dart leaders and K changes as they traverse the previously ionized channels. Thus each operational system may emphasize different stages of the lightning flash, but neither appears to map the entire flash. 1. Introduction Historically, knowledge of lightning behavior has advanced pri•narily through the results of various field observations. Nearly two decades ago, the Time-of-Arrival (TOA) and Interfermnetric (ITF) techniques first presented the opportunity to study the dynamics of lightning with a high degree of spatial and temporal resolution, by mapping lightning radiation initially in two dimensions and later in three [e.g.,

Radio Science, 2012

1] The Earth's geomagnetic field can, in principle, cause significant magnetic-azimuth variations of the lower ionosphere's reflection of 2-150 kHz radio waves emitted by lightning. There has been little published work on this azimuth variation, either modeled or observational. We use broadband emissions from negative cloud-to-ground lightning strokes to study the azimuthal variations systematically. The data are from the Los Alamos Sferic Array, operating in the United States' southern Great Plains during 2005. We compare the observations to a model of lower-ionosphere reflection of radio waves. The model recapitulates the basic features of the time domain reflection waveforms rather well, except at the lowest frequencies. The model transfer function describing the vertical electric field at the receiver is symmetric about 90 magnetic and about 270 magnetic. Two noteworthy features of the azimuth variation are both predicted by the model, and seen in the data: First, at the lowest frequencies (<30 kHz) there is enhanced reflection for eastward propagation, relative to westward propagation. Second, at the higher frequencies (>50 kHz) there is an opposite enhancement, of the reflection for westward propagation, relative to eastward propagation. The westward enhancement at >50 kHz depends sensitively on range and is most evident in nighttime conditions, while the eastward enhancement at <30 kHz occurs at all ranges studied. Range-dependent frequency modulations of the transfer function are the least for magnetic northward propagation (duplicated by magnetic southward).

Journal of Atmospheric and Oceanic Technology, 2005

The lightning data that are recorded with a three-dimensional lightning mapping array (LMA) are compared with data from an electric field change sensor (in this case a flat-plate antenna operated both as a “slow” and a “fast” antenna). The goal of these comparisons is to quantify any time difference that may exist between the initial responses of the two instruments to a lightning flash. The data consist of 136 flashes from two New Mexico thunderstorms. It is found that the initial radiation source detected by the LMA usually precedes the initial response of both the slow and fast antennas. In a small number of cases, the flat-plate antenna response precedes the initial LMA source, but by no more than 2 ms. The observations of such a close time coincidence suggest that the first LMA radiation source of each flash was located at or very near the flash-initiation point. Thus, the first LMA radiation source and the initial sequence of sources from a lightning flash can be used as remot...

2010

Lightning detections of the Catalan Lightning Location Network (XDDE) are compared with high speed video recordings carried out in Spain during summer 2009. At that time the XDDE was composed by four sensors: two SAFIR 3000 type and two LS8000 type. The comparison showed good agreement in the observations at the center and at the south of the network. However, the observations recorded at the north of the network showed a poorer detection efficiency and location accuracy. On the other hand, the fine comparison between frame by frame of video recordings and network detections reveals that the network often detects mostly intra-cloud (IC) sources which probably belong to the preliminary breakdown in downward cloud-to-ground flashes. In some cases few sources are detected during steeped leaders toward to the ground. In the case of our observed IC flashes, the detected sources never corresponded to observations of propagation leaders, if not, small burst of detections were linked to permanent illuminated channels or permanent visible luminosity from the cloud.

IEEE Antennas and Propagation Magazine, 2000

Worldwide lightning location (WWLL) using only 30 lightning sensors has been successfully achieved by using only VLF propagation in the Earth-ionosphere waveguide (EIWG). Ground propagation or mixed "sky" and ground propagation is avoided by requiring evidence of Earth-ionosphere waveguide dispersion. A further requirement is that the lightning strike must be inside the perimeter defined by the lightning sensor sites detecting the stroke. Under these conditions, the time and the location of the stroke can be determined, along with the rms errors. Lightning strokes with errors exceeding 30 Ps or To assist with identifying impulses from the same lightning stroke, the lightning sensor threshold is automatically adjusted to allow an average detection rate of three per second. This largely limits detection to the strongest 4% of all lightning strokes, of which about 40% meet the accuracy requirements for time and location.

Annales Geophysicae, 2007

A simple technique to estimate the distance of the lightning strikes d with a single VLF electromagnetic wave receiver at a single station is described. The technique is based on the recording of oscillatory waveforms of the electric fields of sferics. Even though the process of estimating d using the waveform is a rather classical one, a novel and simple procedure for finding d is proposed in this paper. The procedure adopted provides two independent estimates of the distance of the stroke. The accuracy of measurements has been improved by employing high speed (333 ns sampling rate) signal processing techniques. GPS time is used as the reference time, which enables us to compare the calculated distances of the lightning strikes, by both methods, with those calculated from the data obtained by the WorldWide Lightning Location Network (WWLLN), which uses a multistation technique. The estimated distances of the lightning strikes (77), whose times correlated, ranged from ∼3000-16 250 km. When d<3500 km, the average deviation in d compared with those calculated with the multi-station lightning location system is ∼4.7%, while for all the strokes it was ∼8.8%. One of the lightnings which was recorded by WWLLN, whose field pattern was recorded and the spectrogram of the sferic was also recorded at the site, is analyzed in detail. The deviations in d calculated from the field pattern and from the arrival time of the sferic were 3.2% and 1.5%, respectively, compared to d calculated from the WWLLN location. FFT analysis of the waveform showed that only a narrow band of frequencies is received at the site, which is confirmed by the intensity of the corresponding sferic in the spectrogram.

Journal of Geophysical Research, 2007

We study local time variation in high peak current lightning over land versus over ocean by using lightning locations from the World Wide Lightning Location Network (WWLLN). Optical lightning data from the photodiode detector on the Fast On-Orbit Recording of Transient Events (FORTE) satellite are used to determine the relative detection efficiency of the WWLLN for lightning events by region, as well as over land versus over ocean. We find that the peak lightning flash density varies for the different continents by up to 5 hours in local time. Because the WWLLN measures lightning strokes with large peak currents, the variation in local time of WWLLN-detected strokes suggests a similar variation in local time of transient luminous events (e.g., elves) and their effects on the lower ionosphere.

2003