scholarly journals Study of oblique whistlers in the low-latitude ionosphere, jointly with the C/NOFS satellite and the World-Wide Lightning Location Network

2011 ◽  
Vol 29 (5) ◽  
pp. 851-863 ◽  
Author(s):  
A. R. Jacobson ◽  
R. H. Holzworth ◽  
R. F. Pfaff ◽  
M. P. McCarthy
Keyword(s):  
World Wide ◽  
Low Frequency ◽  
Great Majority ◽  
Detection Algorithm ◽  
Low Latitude ◽  
Automated Algorithm ◽  
The World ◽  
Low Latitude Ionosphere ◽  
Relationship Of ◽  
Vlf Waves

Abstract. 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 low-latitude oscillatory VLF waves seen in this study.

VLF/LF (Very Low Frequency/Low Frequency) Reflection Properties of the Low Latitude Ionosphere

1988 ◽  
Author(s):  
Wayne I. Klemetti ◽  
Paul A. Kossey ◽  
John E. Rasmussen ◽  
Maria Sueli Da Silveira Macedo Moura
Keyword(s):  
Low Frequency ◽  
Low Latitude ◽  
Very Low Frequency ◽  
Low Latitude Ionosphere

Internet regulation: The need for more transparent Internet filtering systems and improved measurement of public opinion on Internet filtering

First Monday ◽  
2011 ◽  
Author(s):  
Nikolaos Koumartzis ◽  
Andreas Veglis
Keyword(s):  
Public Opinion ◽  
World Wide ◽  
National Level ◽  
Great Majority ◽  
Authoritarian Regimes ◽  
Internet Filtering ◽  
Internet Regulation ◽  
Internet Users ◽  
The World ◽  
Western Democracies

All around the world, the phenomenon of Internet regulation is on the rise as more and more countries implement such policies, from Asian authoritarian regimes to Western democracies. At the same time, the great majority of Internet users are not aware that they access a filtered version of World Wide Web due to the “non–transparent” policy of many governments, something that results to a very dangerous precedent for the future of the Internet. In this paper, the authors promote and encourage the participation of Internet users in the designing procedure of Internet Regulation Systems (IRSs), as a way to develop effective and ethically correct systems. This can be done via well–formatted surveys conducted in national level in order to measure public opinion and point out user’s needs. To justify their approach, the authors discuss the results of the available related surveys conducted around the globe. Last, in order to attract researchers in the field, they launched a portal for the International project WebObserver.net (http://webobserver.net/) via which they provide all the needed tools for researchers to conduct such surveys with ease and with the minimum time needed.

scholarly journals A performance assessment of the World Wide Lightning Location Network (WWLLN) via comparison with the Canadian Lightning Detection Network (CLDN)

2010 ◽  
Vol 3 (2) ◽  
pp. 1861-1887 ◽  
Author(s):  
D. Abreu ◽  
D. Chandan ◽  
R. H. Holzworth ◽  
K. Strong
Keyword(s):  
Standard Deviation ◽  
World Wide ◽  
Detection Efficiency ◽  
Low Frequency ◽  
High Peak ◽  
Peak Current ◽  
Lightning Detection ◽  
The World ◽  
The Mean ◽  
The Difference

Abstract. The World Wide Lightning Location Network (WWLLN) uses globally-distributed Very Low Frequency (VLF) receivers in order to observe lightning around the globe. Its objective is to locate as many global strokes as possible, with high temporal and spatial (<10 km) accuracy. Since detection is done in the VLF range, signals from high peak current lightning strokes are able to propagate up to ~104 km before being detected by the WWLLN sensors, allowing for receiving stations to be sparsely spaced. Through a comparison with measurements made by the Canadian Lightning Detection Network (CLDN) between May and August 2008 over a 4° latitude by 4° longitude region centered on Toronto, Canada, this study found that WWLLN detection was most sensitive to high peak current lightning strokes. Events were considered shared between the two networks if they fell within 0.5 ms of each other. Using this criterion, 19 128 WWLLN strokes (analyzed using the Stroke_B algorithm) were shared with CLDN lightning strokes, producing a detection efficiency of 2.8%. The peak current threshold for WWLLN detection is found to be ~20 kA, with the detection efficiency increasing to ~70% at peak currents of ±120 kA. The detection efficiency is seen to have a clear diurnal dependence, with a higher detection efficiency at local midnight than at local noon; this is attributed to the difference in the thickness of the ionospheric D-region between night and day. The mean time difference (WWLLN – CLDN) between shared events was −6.44 μs with a standard deviation of 35 μs, and the mean absolute location accuracy was 7.24 km with a standard deviation of 6.34 km. These results are generally consistent with previous comparison studies of the WWLLN with other regional networks around the world. Additional receiver stations are continuously being added to the network, acting to improve this detection efficiency.

scholarly journals Annual Wave in the world-wide F-Region Ionization

MAUSAM ◽  
2021 ◽  
Vol 10 (1) ◽  
pp. 69-72
Author(s):  
B. N. BHARGAVA
Keyword(s):  
Linear Relationship ◽  
World Wide ◽  
F Region ◽  
A Value ◽  
The World ◽  
Latitude Variation ◽  
Order Of Magnitude ◽  
Annual Component ◽  
Relationship Of ◽  
Made In

An analysis of squares of noon median F2 layer critical frequencies for a 3-year period has been made in order to derive the latitude variation of the annual effect in the electron densities and its relation to average F21ayer ionization. The results indicate that the annual component varies with the latitude in a manner very nearly similar to that of the steady ionization R0 and that for a given value of Ro for any latitude. R1 which can be derived approximately from a linear relationship of the type Rl = 0.3 Ro-4.5. A similar analysis of 9-year data, for precise phase and amplitude of the annual component for a pair of stations yields a value of Rl which is of the same order of magnitude as Ro and which attains a maximum around the epoch of minimum sun-earth distance.

scholarly journals Googling for ‘opposites’: a web-based study of antonym canonicity

Corpora ◽  
2007 ◽  
Vol 2 (2) ◽  
pp. 129-155 ◽  
Author(s):  
Steven Jones ◽  
Carita Paradis ◽  
M. Lynne Murphy ◽  
Caroline Willners
Keyword(s):  
World Wide Web ◽  
World Wide ◽  
Low Frequency ◽  
Limited Range ◽  
Web Based ◽  
The World ◽  
Empirical Perspective ◽  
Discourse Functions ◽  
Large Corpus

This paper seeks to explain why some semantically-opposed word pairs are more likely to be seen as canonical antonyms (for example, cold/hot) than others (icy/scorching, cold/fiery, freezing/hot, etc.). Specifically, it builds on research which has demonstrated that, in discourse, antonyms are inclined to favour certain frames, such as ‘X and Y alike’, ‘from X to Y’ and ‘either X or Y’ (Justeson and Katz, 1991; etc.), and to serve a limited range of discourse functions (Jones, 2002). Our premise is that the more canonical an antonym pair is, the greater the fidelity with which it will occupy such frames. Since an extremely large corpus is needed to identify meaningful patterns of co-occurrence, we turn to Internet data for this research. As well as enabling the notion of antonym canonicity to be revisited from a more empirical perspective, this approach also allows us to evaluate the appropriateness (and assess the risks) of using the World Wide Web as a corpus for studies into certain types of low-frequency textual phenomena.

Lightning‐Generated Whistler Amplitudes Measured by the Van Allen Probes

2021 ◽  
Author(s):  
Thomas Farges ◽  
Jean-Francois Ripoll ◽  
David Malaspina ◽  
Erin Lay ◽  
Gregory Cunningham ◽  
...  
Keyword(s):  
World Wide ◽  
Low Frequency ◽  
Whistler Waves ◽  
Mean Power ◽  
Very Low Frequency ◽  
Van Allen Probes ◽  
Whistler Mode Waves ◽  
The Mean ◽  
Vlf Waves ◽  
Field Wave

&lt;p&gt;This talk will show a statistical analysis of both electric and magnetic field wave amplitudes of very low frequency lightning&amp;#8208;generated whistlers (LGWs) based on the equivalent of 11.5 years of observations made by the Van Allen Probes. We complement this analysis with data from the ground&amp;#8208;based World Wide Lightning Location Network (WWLLN) to explore differences between satellite and ground&amp;#8208;based measurements. We will discuss how LGW mean amplitudes were generally found to be low compared with other whistler mode waves even though there exists extreme events (1 out of 5,000) that can reach 100 pT and contribute strongly to the mean power below L = 2. We will reveal a region of low wave amplitude existing below L=2 thanks to the denser dayside ionosphere, which prevents the intense equatorial lightning VLF waves from propagating through it. Below L = 1.5 at all MLT, LGW amplitudes are found to be weak while the ground&amp;#8208;level lightning activity is maximal. This suggests a difficulty of lightning VLF waves to penetrate / propagate / remain at low L&amp;#8208;shells, certainly due at least to the denser ionosphere during daytime. On the contrary, the mean LGW magnetic power (or RMS) remains nearly constant with respect to L&amp;#8208;shell. We will explain that this is due to strong to extreme LGWs that dominate the wave mean power to the point of compensating the decay of LGW occurrence at low L&amp;#8208;shell. Even though extreme LGW were found to be very powerful, particularly at low L and during night, the mean electric/magnetic power remains low compared with other whistler waves. This implies that LGW resonant effects on electrons are consequently long&amp;#8208;term effects that contribute to &amp;#8220;age&amp;#8221; trapped inner belt electron populations.&lt;/p&gt;

scholarly journals A performance assessment of the World Wide Lightning Location Network (WWLLN) via comparison with the Canadian Lightning Detection Network (CLDN)

2010 ◽  
Vol 3 (4) ◽  
pp. 1143-1153 ◽  
Author(s):  
D. Abreu ◽  
D. Chandan ◽  
R. H. Holzworth ◽  
K. Strong
Keyword(s):  
Standard Deviation ◽  
World Wide ◽  
Detection Efficiency ◽  
Low Frequency ◽  
High Peak ◽  
Peak Current ◽  
Lightning Detection ◽  
The World ◽  
The Mean ◽  
The Difference

Abstract. The World Wide Lightning Location Network (WWLLN) uses globally-distributed Very Low Frequency (VLF) receivers in order to observe lightning around the globe. Its objective is to locate as many global lightning strokes as possible, with high temporal and spatial (< 10 km) accuracy. Since detection is done in the VLF range, signals from high peak current lightning strokes are able to propagate up to ~104 km before being detected by the WWLLN sensors, allowing for receiving stations to be sparsely spaced. Through a comparison with measurements made by the Canadian Lightning Detection Network (CLDN) between May and August 2008 over a 4° latitude by 4° longitude region centered on Toronto, Canada, this study found that WWLLN detection was most sensitive to high peak current lightning strokes. Events were considered shared between the two networks if they fell within 0.5 ms of each other. Using this criterion, 19 128 WWLLN strokes (analyzed using the Stroke_B algorithm) were shared with CLDN lightning strokes, producing a detection efficiency of 2.8%. The peak current threshold for WWLLN detection is found to be ~20 kA, with its detection efficiency increasing from 11.3% for peak currents greater than 20 kA to 75.8% for peak currents greater than 120 kA. The detection efficiency is seen to have a clear diurnal dependence, with a higher detection efficiency at local midnight than at local noon; this is attributed to the difference in the thickness of the ionospheric D-region between night and day. The mean time difference (WWLLN − CLDN) between shared events was −6.44 μs with a standard deviation of 35 μs, and the mean absolute location accuracy was 7.24 km with a standard deviation of 6.34 km. These results are generally consistent with previous comparison studies of the WWLLN with other regional networks around the world. Additional receiver stations are continuously being added to the network, acting to improve this detection efficiency.

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