scholarly journals Unexpected high-frequency “birds”-type VLF emissions.

2020 ◽  
Author(s):  
N.G. Kleimenova ◽  
◽  
J. Manninen ◽  
T. Turunen ◽  
L.I. Gromova ◽  
...  
Keyword(s):  
High Frequency ◽  
Spectral Feature ◽  
Weather Conditions ◽  
Common Source ◽  
Spectral Structure ◽  
Real Nature ◽  
Propagation Behavior ◽  
Lightning Discharges ◽  
Electron Gyrofrequency ◽  
Vlf Emissions

The new typeof daytime natural VLF whistler mode emissions of the magnetospheric origin was recently found in the VLF observations at Kannuslehto station (L ~ 5.5) in Northern Finland.These VLF events occurred at the frequencies above 4-5 kHzeven up to 15 kHz. Here we present the different spectra of this peculiar daytime high-frequency VLF emissions observed under quiet geomagnetic conditions at auroral latitudes at Kannuslehto (Finland) and Lovozero (Russia) stations. These high-frequency waves cannot be attributed to typical well known VLF chorus and hiss. They became visible on the spectrograms only after the filtering out sferics originating by the lightning discharges and hiding all natural high-frequency signals. After this filtering, it was found a large collection of different natural VLF signals observed as a sequence of right-polarized short (less than 1-2 minutes) patches at frequencies above 4-5 kHz, i.e. at higher frequencythan a half the equatorial electron gyrofrequency at the L-shell of Kannuslehto and Lovozero. These emissions were called “birds” due to their chirped sounds. It was established that the “birds” are typically occur during the daytime only under quiet space weather conditions. But in this time, small magnetic substorms were could be observed in the night sector of the Earth. Here we also show the recently observed series of the “bird-mode” emissions with various bizarre quasi-periodic dynamic spectra, sometimes consisting of two (and even more) frequency bands. The “birds” occur simultaneously at Kannuslehto and Lovozero with similar spectral structure demonstrating their common source. It seems that the “birds” emissions are generated deep inside the magnetosphere at the low L-shells. But the real nature, the generation region and propagation behavior of these VLF emissions remain still unknown. Moreover, nobody can explain how the waves could reach the ground at the auroral latitudes like Kannuslehto and Lovozero as well as which magnetospheric driver could generate this very complicated spectral feature of the emissions.

scholarly journals New high-frequency (7–12 kHz) quasi-periodic VLF emissions observed on the ground at <i>L</i>  ∼  5.5

2018 ◽  
Vol 36 (3) ◽  
pp. 915-923 ◽  
Author(s):  
Jyrki Manninen ◽  
Natalia Kleimenova ◽  
Tauno Turunen ◽  
Liudmila Gromova
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Digital Filtering ◽  
Spectral Shape ◽  
Geomagnetic Pulsations ◽  
High Frequency Band ◽  
Polarized Waves ◽  
Electron Gyrofrequency ◽  
Vlf Emissions ◽  
The Waves

Abstract. We reveal previously unknown quasi-periodic (QP) very low frequency (VLF) emissions at the unusually high-frequency band of ∼ 7–12 kHz by applying the digital filtering of strong atmospherics to the ground-based VLF data recorded at Kannuslehto station (KAN). It is located in northern Finland at L ∼ 5.5. The frequencies of QP emissions are much higher than the equatorial electron gyrofrequency at L ∼ 5.5. Thus, these emissions must have been generated at much lower L shells than KAN. Two high-frequency QP emission events have been studied in detail. The emissions were right-hand polarized waves indicating an overhead location of the exit area of waves in the ionosphere. In one event, the spectral–temporal forms of the emissions looked like a series of giant “bullets” due to the very abrupt cessation. Unfortunately, we could not explain such a strange dynamic spectral shape of the waves. In the second event, the modulation period was about 3 min under the absence of simultaneous geomagnetic pulsations. The studied emissions lasted about 4 h and were observed under the very quiet geomagnetic activity. The adequate mechanisms of the generation and propagation of the revealed high-frequency QP emissions have not yet been established. We speculate that studied QP emissions can be attributed to the auto-oscillations of the cyclotron instability in the magnetospheric plasma maser.

scholarly journals Unknown high-frequency (7–12 kHz) quasi-periodic VLF emissions observed on the ground at L ~ 5.5

2018 ◽  
Author(s):  
Jyrki Manninen ◽  
Natalia Kleimenova ◽  
Tauno Turunen ◽  
Liudmila Gromova
Keyword(s):  
Frequency Band ◽  
Geomagnetic Activity ◽  
High Frequency ◽  
Digital Filtering ◽  
Geomagnetic Pulsations ◽  
High Frequency Band ◽  
Polarized Waves ◽  
Electron Gyrofrequency ◽  
Vlf Emissions ◽  
The Waves

Abstract. We reveal previously unknown quasi-periodic (QP) VLF emissions at the unusual high-frequency band of ~ 7–11 kHz by applying the digital filtering of strong sferics to the ground-based VLF data recorded at Kannuslehto station (KAN). It is located in Northern Finland at L ~ 5.5. The frequencies of QP emissions are much higher than the equatorial electron gyrofrequency at L ~ 5.5. Thus, these emissions must have been generated at much lower L-shells than KAN. Two high-frequency QP emission events have been studied in detail. The emissions were right-hand polarized waves indicating an overhead location of the exit area of waves in the ionosphere. In one event, the spectral-temporal forms of the emissions looked like a series of giant bullets with the very abrupt cessation. Unfortunately, we could not explain such strange shape of the waves. In the second event, the modulation period was about 3 min under the absence of the simultaneous geomagnetic pulsations. The studied emissions lasted about 4 hours and were observed under the very quiet geomagnetic activity. The adequate mechanisms of the generation and propagation of the revealed high-frequency QP emissions have not yet been established. We speculate that studied QP emissions can be attributed to the auto-oscillations of the cyclotron instability in the magnetospheric plasma maser.

The Integrated Ocean Observing System High-Frequency Radar Network: Status and Local, Regional, and National Applications

2010 ◽  
Vol 44 (6) ◽  
pp. 122-132 ◽  
Author(s):  
Jack Harlan ◽  
Eric Terrill ◽  
Lisa Hazard ◽  
Carolyn Keen ◽  
Donald Barrick ◽  
...  
Keyword(s):  
High Frequency ◽  
Surface Current ◽  
Water Quality Monitoring ◽  
Velocity Fields ◽  
Common Source ◽  
Integrated Network ◽  
High Frequency Radar ◽  
Radar Network ◽  
Network Status ◽  
Ocean Observing

AbstractA national high-frequency radar network has been created over the past 20 years or so that provides hourly 2-D ocean surface current velocity fields in near real time from a few kilometers offshore out to approximately 200 km. This preoperational network is made up of more than 100 radars from 30 different institutions. The Integrated Ocean Observing System efforts have supported the standards-based ingest and delivery of these velocity fields to a number of applications such as coastal search and rescue, oil spill response, water quality monitoring, and safe and efficient marine navigation. Thus, regardless of the operating institution or location of the radar systems, emergency response managers, and other users, can rely on a common source and means of obtaining and using the data. Details of the history, the physics, and the application of high-frequency radar are discussed with successes of the integrated network highlighted.

scholarly journals The Three-Dimensional Locating of VHF Broadband Lightning Interferometers

Atmosphere ◽  
2018 ◽  
Vol 9 (8) ◽  
pp. 317 ◽  
Author(s):  
Hengyi Liu ◽  
Shi Qiu ◽  
Wansheng Dong
Keyword(s):  
Time Resolution ◽  
High Frequency ◽  
Three Dimensional ◽  
High Time Resolution ◽  
Very High Frequency ◽  
Time Difference Of Arrival ◽  
Lightning Discharges ◽  
Total Lightning ◽  
Locating Information ◽  
Very High

VHF (Very High Frequency) lightning interferometers can locate and observe lightning discharges with a high time resolution. Especially the appearance of continuous interferometers makes the 2-D location of interferometers further improve in time resolution and completeness. However, there is uncertainty in the conclusion obtained by simply analyzing the 2-D locating information. Without the support of other 3-D total lightning locating networks, the 2-station interferometer becomes an option to obtain 3-D information. This paper introduces a 3-D lightning location method of a 2-station broadband interferometer, which uses the theodolite wind measurement method for reference, and gives the simulation results of the location accuracy. Finally, using the multi-baseline continuous 2-D locating method and the 3-D locating method, the locating results of one intra-cloud flash and the statistical results of the initiation heights of 61 cloud-to-ground flashes and 80 intra-cloud flashes are given. The results show that the two-station interferometer has high observation accuracy on both sides of the connection between the two sites. The locating accuracy will deteriorate as the distance between the radiation source and the two stations increases or the height decreases. The actual locating results are similar to those of the existing VHF TDOA (Time Difference of Arrival) lightning locating network.

scholarly journals Emulation of Radius-to-Fix legs in Departure Routes via Fly-By Turns

2019 ◽  
Vol 11 (4) ◽  
pp. 93-106
Author(s):  
Carlos GONZAGA-LOPEZ ◽  
Florian Michael BUCHMANN ◽  
Henrik EKSTRAND ◽  
Andreas LINNÉR ◽  
Philipp Daniel SCHAAD
Keyword(s):  
High Frequency ◽  
Weather Conditions ◽  
Technical Note ◽  
Optimal Management ◽  
Traffic Flows ◽  
Bank Angle ◽  
Constant Radius ◽  
First Results ◽  
Preliminary Study ◽  
Aircraft Type

The results of a preliminary study on the emulation of radius-to-fix legs in turning departures by means of standard track-to-fix legs are presented in this technical note. While radius-to-fix equipage rates keep gradually increasing over time, a traffic mix containing aircraft with and without this navigation capability can impede an optimal management of the traffic flows whenever precise and repeatable curved flight paths are required. After test-flying various sequences of track-to-fix segments to emulate a reference constant-radius arc in a typical departure environment, the deviations to the desired flight path and the flyability aspects were assessed. The first results for a given scenario and aircraft type show an adequate path conformance for a navigation specification RNAV/RNP 1 within a certain range of aircraft performances and weather conditions. However, the reduced predictability of the roll steering when transitioning between track-to-fix segments and the high frequency in the oscillations of the bank angle may pose a problem to flight crews and passengers, respectively.

scholarly journals FOSS4G BASED HIGH FREQUENCY AND INTEROPERABLE LAKE WATER-QUALITY MONITORING SYSTEM

2021 ◽  
Vol XLVI-4/W2-2021 ◽  
pp. 25-29
Author(s):  
M. Cannata ◽  
D. Strigaro ◽  
F. Lepori ◽  
C. Capelli ◽  
M. Rogora ◽  
...  
Keyword(s):  
Open Source ◽  
Monitoring System ◽  
High Frequency ◽  
Algal Blooms ◽  
Weather Conditions ◽  
Water Quality Monitoring ◽  
Lake Ecosystem ◽  
Lake Water Quality ◽  
Lake Ecosystems ◽  
Lake Lugano

Abstract. Climate, together with human activities, is changing the natural dynamics in lake ecosystems and adding new challenges to the management of water resources. Recent studies on Lake Lugano, in Switzerland, showed for instance that the increased water temperature influence other processes such as lake stratification and mixing dynamics, algal blooms, colonisation by alien species, affecting the lake ecosystem as a whole. In such situation, real-time systems with high frequency measurements, together with the traditional discrete monitoring, can help in understanding dynamics and processes occurring on short time scales. To this aim, an open monitoring system largely composed by open source components is being developed for the high frequency monitoring of Lake Lugano. The system relies on the open source software istSOS either on the server and node sides applying the edge computing paradigm which is more and more adopted in the Internet of Things field. The implementation collects temperature and dissolved oxygen data from sensors positioned at six different depths of the lake and transmits them using the LoRa radio frequency to a data warehouse. At server side, the software architecture adopts the evolving technology based on containers where services can be grouped in a compose and easily deployed on a server. This paper aims to describe the adopted open source technology and demonstrate that it can be successfully used also in environmental monitoring where the accessibility is limited and the weather conditions can be unpredictable.

scholarly journals On the use of ELF/VLF emissions triggered by HAARP to simulate PLHR and to study associated MLR events

2022 ◽  
Vol 74 (1) ◽  
Author(s):  
Michel Parrot ◽  
Frantisěk Němec ◽  
Morris B. Cohen ◽  
Mark Gołkowski
Keyword(s):  
Spectral Analysis ◽  
Time Delay ◽  
High Frequency ◽  
Conjugate Point ◽  
Physical Processes ◽  
Line Radiation ◽  
Harmonic Radiation ◽  
Frequency Spacing ◽  
Low Altitude ◽  
Vlf Emissions

AbstractA spectrogram of Power Line Harmonic Radiation (PLHR) consists of a set of lines with frequency spacing corresponding exactly to 50 or 60 Hz. It is distinct from a spectrogram of Magnetospheric Line Radiation (MLR) where the lines are not equidistant and drift in frequency. PLHR and MLR propagate in the ionosphere and the magnetosphere and are recorded by ground experiments and satellites. If the source of PLHR is evident, the origin of the MLR is still under debate and the purpose of this paper is to understand how MLR lines are formed. The ELF waves triggered by High-frequency Active Auroral Research Program (HAARP) in the ionosphere are used to simulate lines (pulses of different lengths and different frequencies). Several receivers are utilized to survey the propagation of these pulses. The resulting waves are simultaneously recorded by ground-based experiments close to HAARP in Alaska, and by the low-altitude satellite DEMETER either above HAARP or its magnetically conjugate point. Six cases are presented which show that 2-hop echoes (pulses going back and forth in the magnetosphere) are very often observed. The pulses emitted by HAARP return in the Northern hemisphere with a time delay. A detailed spectral analysis shows that sidebands can be triggered and create elements with superposed frequency lines which drift in frequency during the propagation. These elements acting like quasi-periodic emissions are subjected to equatorial amplification and can trigger hooks and falling tones. At the end all these known physical processes lead to the formation of the observed MLR by HAARP pulses. It is shown that there is a tendency for the MLR frequencies of occurrence to be around 2 kHz although the exciting waves have been emitted at lower and higher frequencies. Graphical Abstract

scholarly journals An outbreak of Aspergillus species in response to environmental conditions in Serbia

2013 ◽  
Vol 28 (3) ◽  
pp. 167-179 ◽  
Author(s):  
Jelena Levic ◽  
Snezana Gosic-Dondo ◽  
Dragica Ivanovic ◽  
Slavica Stankovic ◽  
Vesna Krnjaja ◽  
...  
Keyword(s):  
Ostrinia Nubilalis ◽  
High Frequency ◽  
European Corn Borer ◽  
Weather Conditions ◽  
Very High Frequency ◽  
Crop Species ◽  
Corn Borer ◽  
The Past ◽  
Maize Grain ◽  
Very High

The frequency and incidence of A. flavus and A. niger on barley, maize, soybean, sunflower and wheat grain, the abundance of European corn borer (Ostrinia nubilalis) moths and their interaction depending on weather conditions in the 2008-2012 period were studied. Under the agroecological conditions of Serbia, the species A. niger is more frequent than A. flavus, and concerning the crop species, its frequency is highest in kernels of sunflower, than soybean, maize, barley and wheat. A. flavus was extremely dominant on all plant species in 2012 regarding its frequency: 100% on soybean, 95.3% on maize, 65.2% on barley, 57.1% on sunflower and 45.8% on wheat. Furthermore, the incidence of A. flavus was higher in 2012 than in previous years. The uncommonly high frequency and incidence of A. flavus infestation of maize grain in 2012 were caused by extremely stressful agrometeorological conditions, high temperatures and drought over the period from flowering to waxy maturity of maize. The precipitation factor (Pf = precipitation sum / average monthly temperature) showed that 2012 was extremely arid in June (Pf = 0.57), July (Pf = 1.45), August (Pf = 0.15) and September (Pf = 1.42). European corn borer (ECB) was a second factor causing intensive occurrence of A. flavus on maize grain in 2012. The maximum flight of ECB moths was recorded as early as in July (5,149) and, as a result of this, high damage and numerous injuries were detected at harvest. Those injuries were covered by visible olive-green powdery colonies typical of A. flavus. In the chronology of A. flavus occurrence, these are the first data on its very high frequency and incidence under the agroecological conditions of Serbia. As intensive infections with A. flavus were rare in the past 50 years, the level of aflatoxins in maize grain was low.

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