Very low latitude ( L = 1.08) whistlers and correlation with lightning activity (original) (raw)
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One-to-one relation with its causative lightning discharges and propagation features of night-time whistlers recorded at low-latitude station, Allahabad (geomag. lat. 16.05°N, L = 1.08), India, from continuous observations made during 1-7 April, 2011 have been studied. The whistler observations were made using the Automatic Whistler Detector (AWD) system and AWESOME VLF receiver. The causative lightning strikes of whistlers were checked in data provided by World-Wide Lightning Location Network (WWLLN). A total of 32 whistlers were observed out of which 23 were correlated with their causative lightnings in and around the conjugate location (geom. lat. 9.87°S) of Allahabad. A multi-flash whistler is also observed on 1 April with dispersions 15.3, 17.5 and 13.6 s 1/2 . About 70% (23 out of 32) whistlers were correlated with the WWLLN detected causative lightnings in the conjugate region which supports the ducted mode of propagation at low latitude. The multi-flash and short whistlers also propagated most likely in the ducted mode to this station.
Correlation between global lightning and whistlers observed at Tihany, Hungary
Journal of Geophysical Research, 2009
Although the generation and propagation mechanisms for whistlers are fairly well understood, the location and extent of the lightning source region for the whistlers observed at a given station are currently unknown. 15 The correlation of whistler observations against global lightning data allows an estimate of the size and position of the source region. For whistlers detected at Tihany, Hungary, an area of positive correlation with radius ∼ 1000 km was found to be centred on the conjugate point. Although the maximal sample correlation coefficient was relatively low, r = 0.065, it has a high statistical sig-20 nificance, indicating that it is extremely improbable that the whistlers and lightning in this region are actually uncorrelated. Other smaller areas of positive correlation were found further afield in South America and the Maritime Continent.
Annales Geophysicae, 2011
We use the C/NOFS satellite's Vector Electric Field Instrument (VEFI) to study the relationship of impulsive electron whistlers in the low-latitude ionosphere to lightning strokes located by the World-Wide Lightning Location Network (WWLLN). In order to systematize this work, we develop an automated algorithm for recognizing and selecting the signatures of electron whistlers amongst many Very Low Frequency (VLF) recordings provided by VEFI. We demonstrate the application of this whistler-detection algorithm to data mining of a ∼ two-year archive of VEFI recordings. It is shown that the relatively simple oblique electron whistler adequately accounts of the great majority of lowlatitude oscillatory VLF waves seen in this study.
Whistler-Lightning Correlations: Significant or Coincidence?
It is well known that the impulsive VLF emissions produced by lightning strikes travel extraordinary distances in the Earth-ionosphere waveguide. Whistlers observed on the ground are thought to be produced by the dispersive transmission of these impulses along field-aligned ducts of enhanced or depleted plasma density through the magnetosphere. Lightning strikes in one hemisphere are thus responsible for whistlers recorded in the opposite hemisphere. The meagre attenuation of these signals in the waveguide, however, implies that neither the source lightning discharge nor the receiver need necessarily be located close to the footpoints of the magnetic field line. Using a cross-correlation technique we reveal the most likely location of the lightning strikes responsible for whistlers recorded at Tihany, Hungary, and Dunedin, New Zealand. The latter location is of particular interest due to the anomalous diurnal variation in whistler occurrence.
Whistlers detected and analyzed by Automatic Whistler Detector (AWD) at low latitude Indian stations
Journal of Atmospheric and Solar-Terrestrial Physics, 2014
Recently, at three Indian low latitude stations: Varanasi (geomag. lat. 14155 0 N, geomag. long. 153154 0 E, L: 1.078), Allahabad (geomag. lat. 16.051N; geomag. long. 155.341E, L: 1.081) and Lucknow (geomag. lat. 17.61N, geomag. long. 154.51E, L: 1.104) an Automatic Whistler Detector (AWD) has been installed in December, 2010 for detection and analysis of whistlers. This instrument automatically detects and collects statistical whistlers data for the investigation of whistlers generation and propagation. Large numbers of whistlers have been recorded at Varanasi and Allahabad during the year 2011 which is analyzed in the present study. Different types of whistlers have been recorded at Varanasi and Allahabad. The correlation between recorded whistlers and causative lightning strikes were analyzed using data provided by World-Wide Lightning Location Network (WWLLN). We observed that for both the stations more than 50% of causative sferics of whistlers were observed to match closely with the times of WWLLN detected lightning strikes within the propagation times of causative tweeks. All of these lightning strikes originated from the region within 500-600 km radius circle from the conjugate point of Varanasi and Allahabad supports the ducted propagation at low latitude stations. The dispersion of the observed whistlers varies between 8 and 18 s 1/2 , which shows that the observed whistlers have propagated in ducted mode and whole propagation path of whistlers lies in the ionosphere. The ionospheric columnar electron contents of these observed whistlers vary between 13.21 TECU and 56.57 TECU. The ionospheric parameters derived from whistler data at Varanasi compare well with the other measurements made by other techniques.
Global lightning distribution and whistlers observed at Dunedin, New Zealand
Annales Geophysicae, 2010
Whistlers observed at Dunedin, New Zealand, are an enigma since they do not conform to the classical model of whistler production developed by . It is generally accepted that the causative lightning stroke for a whistler observed on the ground at a particular location was located in the neighbourhood of the conjugate point, and generated an electromagnetic signal which propagated in a plasmaspheric duct stretched along a magnetic field line linking the two hemispheres. The causative stroke is thought to have occurred within reasonable proximity of one footpoint of this field line, while the observer was located in the vicinity of the other footpoint. Support for this model has come from a number of previous studies of whistler-lightning observations and whistler-induced particle precipitation. However, as demonstrated here, this model does not always apply.
Annales Geophysicae, 2006
Lightning Imaging Sensor (LIS) data have been analysed to ascertain the statistical pattern of lightning occurrence over southern Africa. The diurnal and seasonal variations are mapped in detail. The highest flash rates (107.2 km −2 y −1 ) occur close to the equator but maxima are also found over Madagascar (32.1 km −2 y −1 ) and South Africa (26.4 km −2 y −1 ). A feature of the statistics is a relatively steady contribution from over the ocean off the east coast of South Africa that appears to be associated with the Agulhas current.
Thunderstorms, Lightning, Sprites and Magnetospheric Whistler-Mode Radio Waves
Surveys in Geophysics, 2008
Thunderstorms and the lightning that they produce are inherently interesting phenomena that have intrigued scientists and mankind in general for many years. The study of thunderstorms has rapidly advanced during the past century and many efforts have been made towards understanding lightning, thunderstorms and their consequences. Recent observations of optical phenomena above an active lightning discharge along with the availability of modern technology both for data collection and data analysis have renewed interest in the field of thunderstorms and their consequences in the biosphere. In this paper, we review the electrification processes of a thunderstorm, lightning processes and their association with global electric circuit and climate. The upward lightning discharge can cause sprites, elves, jets, etc. which are together called transient luminous events.