scholarly journals Calculating ultra-low-frequency wave power of the compressional magnetic field vs. <i>L</i> and time: multi-spacecraft analysis using the Van Allen probes, THEMIS and GOES

2016 ◽  
Vol 34 (6) ◽  
pp. 565-571 ◽  
Author(s):  
Theodore E. Sarris ◽  
Xinlin Li
Keyword(s):  
Diffusion Processes ◽  
Low Frequency ◽  
Time History ◽  
Energetic Particles ◽  
Radial Diffusion ◽  
Wave Power ◽  
Frequency Wave ◽  
Wave Numbers ◽  
Van Allen Probes ◽  
History Of

Abstract. Ultra-low-frequency (ULF) pulsations are critical in radial diffusion processes of energetic particles, and the power spectral density (PSD) of these fluctuations is an integral part of the radial diffusion coefficients and of assimilative models of the radiation belts. Using simultaneous measurements from two Geostationary Operational Environmental Satellites (GOES) geosynchronous satellites, three satellites of the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft constellation and the two Van Allen probes during a 10-day period of intense geomagnetic activity and ULF pulsations of October 2012, we calculate the PSDs of ULF pulsations at different L shells. By following the time history of measurements at different L it is shown that, during this time, ULF wave power is not enhanced uniformly throughout the magnetosphere but instead is mostly enhanced in the outer L shells, close to the magnetopause, and to a lesser extent in the inner magnetosphere, closer to the plasmapause. Furthermore, by using phase differences between two GOES geosynchronous satellite pairs, we estimate the daily-averaged distribution of power at different azimuthal wave numbers. These results can have significant implications in better defining the effect of radial diffusion in the phase space density of energetic particles for different wave numbers or L shell distributions of ULF power.

scholarly journals Strange VLF bursts in northern Scandinavia: case study of the afternoon "mushroom-like" hiss on 8 December 2013

2015 ◽  
Vol 33 (8) ◽  
pp. 991-995 ◽  
Author(s):  
J. Manninen ◽  
N. G. Kleimenova ◽  
A. Kozlovsky ◽  
I. A. Kornilov ◽  
L. I. Gromova ◽  
...  
Keyword(s):  
Low Frequency ◽  
Mutual Effect ◽  
Time History ◽  
Lower Ionosphere ◽  
Wave Interaction ◽  
Recovery Phase ◽  
Frequency Wave ◽  
Left Hand ◽  
Very Low Frequency ◽  
The Right

Abstract. We investigate a non-typical very low frequency (VLF) 1–4 kHz hiss representing a sequence of separated noise bursts with a strange "mushroom-like" shape in the frequency–time domain, each one lasting several minutes. These strange afternoon VLF emissions were recorded at Kannuslehto (KAN, &amp;varphi; = 67.74° N, λ = 26.27° E; L ∼ 5.5) in northern Finland during the late recovery phase of the small magnetic storm on 8 December 2013. The left-hand (LH) polarized 2–3 kHz "mushroom caps" were clearly separated from the right-hand (RH) polarized "mushroom stems" at the frequency of about 1.8–1.9 kHz, which could match the lower ionosphere waveguide cutoff (the first transverse resonance of the Earth–ionosphere cavity). We hypothesize that this VLF burst sequence could be a result of the modulation of the VLF hiss electron–cyclotron instability from the strong Pc5 geomagnetic pulsations observed simultaneously at ground-based stations as well as in the inner magnetosphere by the Time History of Events and Macroscale Interactions during Substorms mission probe (THEMIS-E; ThE). This assumption is confirmed by a similar modulation of the intensity of the energetic (1–10 keV) electrons simultaneously observed by the same ThE spacecraft. In addition, the data of the European Incoherent Scatter Scientific Association (EISCAT) radar at Tromsø show a similar quasi-periodicity in the ratio of the Hall-to-Pedersen conductance, which may be used as a proxy for the energetic particle precipitation enhancement. Our findings suggest that this strange mushroom-like shape of the considered VLF hiss could be a combined mutual effect of the magnetospheric ULF–VLF (ultra low frequency–very low frequency) wave interaction and the ionosphere waveguide propagation.

Study on the Uplift Force of Plunge Pool Slab

2014 ◽  
Vol 580-583 ◽  
pp. 1897-1900
Author(s):  
Chun Tao Wang ◽  
Bang Hua Xie ◽  
Wen Hui Zeng
Keyword(s):  
Low Frequency ◽  
Time History ◽  
Uplift Force ◽  
Plunge Pool ◽  
Discharge Water ◽  
Amplitude Vibration ◽  
History Of ◽  
Force Time ◽  
The Impact ◽  
Test Result

The impact of the flood discharge water flow from a high dam is rather great on the slab of a plunge pool, and may cause damages to the plunge pool and consequently endangers the dam body safety. Therefore, a reverse arch slab model was established on the base of a study on and a simulation of the rational scale of gaps between the plates of the plunge pool slab. The model was an arch ring containing 7 slabs. The uplift force time history of each slab was measured, and the uplift force power spectrum and probability density were analyzed. The test result shows that the uplift energy mainly centers in 0-15Hz frequency bandwidth, and mostly within 1Hz. It belongs to a low frequency and big amplitude vibration.

scholarly journals Multipoint spacecraft observations of long-lasting poloidal Pc4 pulsations in the dayside magnetosphere on 1–2 May 2014

2016 ◽  
Vol 34 (11) ◽  
pp. 985-998 ◽  
Author(s):  
Galina Korotova ◽  
David Sibeck ◽  
Mark Engebretson ◽  
John Wygant ◽  
Scott Thaller ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Time History ◽  
Satellite System ◽  
Local Times ◽  
Spectral Structure ◽  
Nodal Structure ◽  
Van Allen Probes ◽  
History Of ◽  
Solar Wind Parameters ◽  
The Magnetic Field

Abstract. We use magnetic field and plasma observations from the Van Allen Probes, Time History of Events and Macroscale Interactions during Substorms (THEMIS) and Geostationary Operational Environmental Satellite system (GOES) spacecraft to study the spatial and temporal characteristics of long-lasting poloidal Pc4 pulsations in the dayside magnetosphere. The pulsations were observed after the main phase of a moderate storm during low geomagnetic activity. The pulsations occurred during various interplanetary conditions and the solar wind parameters do not seem to control the occurrence of the pulsations. The most striking feature of the Pc4 magnetic field pulsations was their occurrence at similar locations during three of four successive orbits. We used this information to study the latitudinal nodal structure of the pulsations and demonstrated that the latitudinal extent of the magnetic field pulsations did not exceed 2 Earth radii (RE). A phase shift between the azimuthal and radial components of the electric and magnetic fields was observed from ZSM  =  0.30 RE to ZSM  =  −0.16 RE. We used magnetic and electric field data from Van Allen Probes to determine the structure of ULF waves. We showed that the Pc4 magnetic field pulsations were radially polarized and are the second-mode harmonic waves. We suggest that the spacecraft were near a magnetic field null during the second orbit when they failed to observe the magnetic field pulsations at the local times where pulsations were observed on previous and successive orbits. We investigated the spectral structure of the Pc4 pulsations. Each spacecraft observed a decrease of the dominant period as it moved to a smaller L shell (stronger magnetic field strength). We demonstrated that higher frequencies occurred at times and locations where Alfvén velocities were greater, i.e., on Orbit 1. There is some evidence that the periods of the pulsations increased during the plasmasphere refilling following the storm.

scholarly journals Repeating Earthquakes During Multiple Phases of Unrest and Eruption at Mount Agung, Bali, Indonesia, 2017

2021 ◽  
Vol 9 ◽  
Author(s):  
John J. Wellik ◽  
Stephanie G. Prejean ◽  
Devy K. Syahbana
Keyword(s):  
Seismic Activity ◽  
Low Frequency ◽  
Time History ◽  
Seismic Energy ◽  
Transition Phase ◽  
Repeating Earthquakes ◽  
Waveform Similarity ◽  
History Of ◽  
Shallow Crust ◽  
Insight Into

In 2017, Mount Agung produced a small (VEI 2) eruption that was preceded by an energetic volcano-tectonic (VT) swarm (&gt;800 earthquakes per day up to M4.9) and two months of declining activity. The period of decreased seismic activity complicated forecasting efforts for scientists monitoring the volcano. We examine the time history of earthquake families at Mount Agung in search of additional insight into the temporal changes in the shallow crust prior to eruption. Specifically, we analyze the period of declining seismic activity about five weeks prior to the eruption when forecasting uncertainty was greatest. We use REDPy (Hotovec-Ellis and Jeffries, 2016) to build a catalog of 6,508 earthquakes from 18 October 2017–15 February 2018 and group them into families of repeating earthquakes based on waveform similarity using a cross-correlation coefficient threshold of 0.8. We show that the evolution of earthquake families provides evidence that Mount Agung was progressing toward eruption even though overall earthquake rates and seismic-energy-release declined. We find that earthquake families that dominated seismicity during the beginning of the crisis ceased near the onset of tremor on 12 November 2017. Then, earthquake families took on characteristics commonly observed during effusive phases of eruptions on 15 November—a full six days before the first phreatomagmatic eruption on 21 November 2017 and a full ten days before the actual onset of lava effusion on 25 November 2017. We interpret the transitions in seismicity as the manifestation of a three-phase physical model including an Intrusion Phase, a Transition Phase, and a Eruptive Phase. During the Intrusion Phase, seismicity was dominated by VT earthquakes with a relatively high percentage of repeaters (59%) grouped into numerous (65) simultaneous families. During the Eruptive Phase, seismicity included both VT and low frequency earthquakes that grouped into relatively long-lived families despite a low overall percentage of repeaters (14%). The Transition Phase exhibited characteristics of earthquake families between the Intrusion Phase and Eruptive Phase. We conclude that the time history of earthquake families provides insight into the evolution of the stress distribution in the volcanic edifice, the development of the volcanic conduit, and seismogenesis of magma effusion. Finally, we discuss the role that repeating earthquakes could play in real-time monitoring at restless volcanoes. Our work suggests eruption forecasts can be improved by incorporating automatic processing codes to assist seismologists during sustained periods of high earthquake rates, even at sparsely monitored volcanoes.

scholarly journals Magnetohydrodynamic modeling of three Van Allen Probes storms in 2012 and 2013

2015 ◽  
Vol 33 (8) ◽  
pp. 1037-1050 ◽  
Author(s):  
J. Paral ◽  
M. K. Hudson ◽  
B. T. Kress ◽  
M. J. Wiltberger ◽  
J. R. Wygant ◽  
...  
Keyword(s):  
Electric Field ◽  
Low Frequency ◽  
Propagation Speed ◽  
Outer Zone ◽  
Wave Power ◽  
Radial Transport ◽  
Simulation Code ◽  
Azimuthal Component ◽  
Ulf Wave ◽  
Van Allen Probes

Abstract. Coronal mass ejection (CME)-shock compression of the dayside magnetopause has been observed to cause both prompt enhancement of radiation belt electron flux due to inward radial transport of electrons conserving their first adiabatic invariant and prompt losses which at times entirely eliminate the outer zone. Recent numerical studies suggest that enhanced ultra-low frequency (ULF) wave activity is necessary to explain electron losses deeper inside the magnetosphere than magnetopause incursion following CME-shock arrival. A combination of radial transport and magnetopause shadowing can account for losses observed at radial distances into L = 4.5, well within the computed magnetopause location. We compare ULF wave power from the Electric Field and Waves (EFW) electric field instrument on the Van Allen Probes for the 8 October 2013 storm with ULF wave power simulated using the Lyon–Fedder–Mobarry (LFM) global magnetohydrodynamic (MHD) magnetospheric simulation code coupled to the Rice Convection Model (RCM). Two other storms with strong magnetopause compression, 8–9 October 2012 and 17–18 March 2013, are also examined. We show that the global MHD model captures the azimuthal magnetosonic impulse propagation speed and amplitude observed by the Van Allen Probes which is responsible for prompt acceleration at MeV energies reported for the 8 October 2013 storm. The simulation also captures the ULF wave power in the azimuthal component of the electric field, responsible for acceleration and radial transport of electrons, at frequencies comparable to the electron drift period. This electric field impulse has been shown to explain observations in related studies (Foster et al., 2015) of electron acceleration and drift phase bunching by the Energetic Particle, Composition, and Thermal Plasma Suite (ECT) instrument on the Van Allen Probes.

scholarly journals Cluster observations of particle acceleration up to supra-thermal energies in the cusp region related to low-frequency wave activity – possible implications for the substorm initiation process

2008 ◽  
Vol 26 (3) ◽  
pp. 653-669 ◽  
Author(s):  
I. I. Vogiatzis ◽  
T. E. Sarris ◽  
E. T. Sarris ◽  
O. Santolík ◽  
I. Dandouras ◽  
...  
Keyword(s):  
Particle Acceleration ◽  
Particle Interaction ◽  
Power Spectra ◽  
Low Frequency ◽  
Wave Activity ◽  
Wave Power ◽  
Frequency Wave ◽  
Cusp Region ◽  
Propagation Parameters ◽  
Local Wave

Abstract. The purpose of our study is to investigate the way particles are accelerated up to supra-thermal energies in the cusp diamagnetic cavities. For this reason we have examined a number of Cluster cusp crossings, originally identified by Zhang et al. (2005), for the years 2001 and 2002 using data from RAPID, STAFF, EFW, CIS, PEACE, and FGM experiments. In the present study we focus on two particular cusp crossings on 25 March 2002 and on 10 April 2002 which demonstrate in a clear way the general characteristics of the events in our survey. Both events exhibit very sharp spatial boundaries seen both in CNO (primarily single-charged oxygen of ionospheric origin based on CIS observations) and H+ flux increases within the RAPID energy range with the magnetic field intensity being anti-correlated. Unlike the first event, the second one shows also a moderate electron flux increase. The fact that the duskward electric field Ey has relatively low values <5 mV/m while the local wave activity is very intense provides a strong indication that particle energization is caused primarily by wave-particle interactions. The wave power spectra and propagation parameters during these cusp events are examined in detail. It is concluded that the high ion fluxes and at the same time the presence or absence of any sign of energization in the electrons clearly shows that the particle acceleration depends on the wave power near the local particle gyrofrequency and on the persistence of the wave-particle interaction process before particles escape from cusp region. Furthermore, the continuous existence of energetic O+ ions suggests that energetic O+ populations are of spatial nature at least for the eight events that we have studied so far.

scholarly journals Radial diffusion simulations of the 20 September 2007 radiation belt dropout

2014 ◽  
Vol 32 (8) ◽  
pp. 925-934 ◽  
Author(s):  
J. Albert
Keyword(s):  
Pitch Angle ◽  
Radiation Belt ◽  
Outer Boundary ◽  
Time History ◽  
Radial Diffusion ◽  
Time Interval ◽  
Resonant Interactions ◽  
Magnetic Field Model ◽  
History Of ◽  
Electromagnetic Ion Cyclotron Waves

Abstract. This is a study of a dropout of radiation belt electrons, associated with an isolated solar wind density pulse on 20 September 2007, as seen by the solid-state telescopes (SST) detectors on THEMIS (Time History of Events and Macroscale Interactions during Substorms). Omnidirectional fluxes were converted to phase space density at constant invariants M = 700 MeV G−1 and K = 0.014 RE G1/2, with the assumption of local pitch angle α &amp;approx; 80° and using the T04 magnetic field model. The last closed drift shell, which was calculated throughout the time interval, never came within the simulation outer boundary of L* = 6. It is found, using several different models for diffusion rates, that radial diffusion alone only allows the data-driven, time-dependent boundary values at Lmax = 6 and Lmin = 3.7 to propagate a few tenths of an RE during the simulation; far too slow to account for the dropout observed over the broad range of L* = 4–5.5. Pitch angle diffusion via resonant interactions with several types of waves (chorus, electromagnetic ion cyclotron waves, and plasmaspheric and plume hiss) also seems problematic, for several reasons which are discussed.

scholarly journals On the origin of falling-tone chorus elements in Earth's inner magnetosphere

2014 ◽  
Vol 32 (12) ◽  
pp. 1477-1485 ◽  
Author(s):  
H. Breuillard ◽  
O. Agapitov ◽  
A. Artemyev ◽  
V. Krasnoselskikh ◽  
O. Le Contel ◽  
...  
Keyword(s):  
Numerical Models ◽  
Low Frequency ◽  
Time History ◽  
Field Measurements ◽  
Inner Magnetosphere ◽  
Chorus Waves ◽  
History Of ◽  
Power Frequency ◽  
Statistical Studies ◽  
Good Agreement

Abstract. Generation of extremely/very low frequency (ELF/VLF) chorus waves in Earth's inner magnetosphere has received increased attention recently because of their significance for radiation belt dynamics. Though past theoretical and numerical models have demonstrated how rising-tone chorus elements are produced, falling-tone chorus element generation has yet to be explained. Our new model proposes that weak-amplitude falling-tone chorus elements can be generated by magnetospheric reflection of rising-tone elements. Using ray tracing in a realistic plasma model of the inner magnetosphere, we demonstrate that rising-tone elements originating at the magnetic equator propagate to higher latitudes. Upon reflection there, they propagate to lower L-shells and turn into oblique falling tones of reduced power, frequency, and bandwidth relative to their progenitor rising tones. Our results are in good agreement with comprehensive statistical studies of such waves, notably using magnetic field measurements from THEMIS (Time History of Events and Macroscale Interactions during Substorms) spacecraft. Thus, we conclude that the proposed mechanism can be responsible for the generation of weak-amplitude falling-tone chorus emissions.

Ultra-low-frequency wave power in the magnetotail lobes 1. Relation to substorm Onsets and the auroral electrojet index

1990 ◽  
Vol 17 (11) ◽  
pp. 1845-1848 ◽  
Author(s):  
R. A. Smith ◽  
M. L. Goldstein ◽  
M. R. Sands ◽  
R. P. Lepping ◽  
C. K. Goertz ◽  
...  
Keyword(s):  
Low Frequency ◽  
Auroral Electrojet ◽  
Wave Power ◽  
Frequency Wave ◽  
Substorm Onsets

Numerical Approaches to Movement of Suspended Cable under Wind Based on VFIFE

2011 ◽  
Vol 255-260 ◽  
pp. 1252-1255
Author(s):  
Zhen Yu Zhong
Keyword(s):  
Low Frequency ◽  
Time History ◽  
Cable Structure ◽  
Suspended Cable ◽  
Linear Behavior ◽  
Wide Range ◽  
Non Linear ◽  
History Of ◽  
Linear Problems ◽  
Dynamics Response

Dynamics response of suspended cable structure is studied in this paper. It is difficult to analyze this type of structure because of non-linear behavior. VFIFE is an efficient method to solve non-linear problems and applied to calculate movement of cable on wide range. Some results are obtained from time history of cable vibration, such as galloping and characteristic frequency. A case of cable movement under wind shows that low frequency in wind speed is main fact impacting on wave of cable.

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