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.

Electroencephalogram analysis of non-rapid eye movement sleep in rats

1988 ◽  
Vol 255 (1) ◽  
pp. R27-R37 ◽  
Author(s):  
L. Trachsel ◽  
I. Tobler ◽  
A. A. Borbely
Keyword(s):  
Eye Movement ◽  
Slow Wave ◽  
Power Spectra ◽  
Low Frequency ◽  
Wave Activity ◽  
Slow Wave Activity ◽  
Rapid Eye Movement ◽  
Rapid Eye Movement Sleep ◽  
Episode Duration ◽  
High Frequency Activity

Sleep states and power spectra of the electroencephalogram were determined for consecutive 4-s epochs during 24 h in rats that had been implanted with electrodes under deep pentobarbital anesthesia. The power spectra in non-rapid eye movement sleep (NREMS) showed marked trends: low-frequency activity (0.75-7.0 Hz) declined progressively throughout the 12-h light period (L) and remained low during most of the 12-h dark period (D); high-frequency activity (10.25-25.0 Hz) rose toward the end of L and reached a maximum at the beginning of D. Within a single NREMS episode (duration 0.5-5.0 min), slow-wave activity (0.75-4.0 Hz) increased progressively to a plateau level. The rise was approximated by a saturating exponential function: although the asymptote level of the function showed a prominent 24-h rhythm, the time constant remained relatively stable (approximately 40 s). After short interruptions of NREMS episodes, slow-wave activity rose more steeply than after long interruptions. The marked 24-h variation of maximum slow-wave activity within NREMS episodes may reflect the level of a homeostatic sleep process.

scholarly journals Low frequency wave sources in the outer magnetosphere, magnetosheath, and near Earth solar wind

2007 ◽  
Vol 25 (10) ◽  
pp. 2217-2228 ◽  
Author(s):  
O. D. Constantinescu ◽  
K.-H. Glassmeier ◽  
P. M. E. Décréau ◽  
M. Fränz ◽  
K.-H. Fornaçon
Keyword(s):  
Solar Wind ◽  
Low Frequency ◽  
High Concentration ◽  
Frequency Wave ◽  
Magnetic Field Data ◽  
Spherical Waves ◽  
Cusp Region ◽  
Outer Magnetosphere ◽  
Lower Extent ◽  
Broad Variety

Abstract. The interaction of the solar wind with the Earth magnetosphere generates a broad variety of plasma waves through different mechanisms. The four Cluster spacecraft allow one to determine the regions where these waves are generated and their propagation directions. One of the tools which takes full advantage of the multi-point capabilities of the Cluster mission is the wave telescope technique which provides the wave vector using a plane wave representation. In order to determine the distance to the wave sources, the source locator – a generalization of the wave telescope to spherical waves – has been recently developed. We are applying the source locator to magnetic field data from a typical traversal of Cluster from the cusp region and the outer magnetosphere into the magnetosheath and the near Earth solar wind. We find a high concentration of low frequency wave sources in the electron foreshock and in the cusp region. To a lower extent, low frequency wave sources are also found in other magnetospheric regions.

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 Local Wave Activity and the Onset of Blocking along a Potential Vorticity Front

2017 ◽  
Vol 74 (7) ◽  
pp. 2341-2362 ◽  
Author(s):  
Noboru Nakamura ◽  
Clare S. Y. Huang
Keyword(s):  
Layer Thickness ◽  
Potential Vorticity ◽  
Wave Train ◽  
Low Frequency ◽  
Vortex Pair ◽  
Zonal Flow ◽  
Wave Activity ◽  
Thickness Variation ◽  
Westerly Jet ◽  
Local Wave

Abstract Interaction between a train of transient waves and a diffluent westerly jet is examined using a regional quasigeostrophic equivalent barotropic model with a (nearly) binary potential vorticity (PV) distribution. Unlike most previous studies, but consistent with the observed extratropical tropopause, cross-stream variation in the layer thickness is allowed to contribute to the discontinuity in PV. In all cases examined, short (i.e., barotropic) edge waves are continuously forced in the upstream, then migrate downstream, and eventually exit the domain. A quasilinear 1D theory based on the conservation of local wave activity predicts that no steady wave train can be maintained where the westerly zonal flow is decelerated below one-half of the initial value, at which point the wave envelope develops a migratory shock analogous to the Lighthill–Whitham–Richards traffic flow problem. Fully nonlinear high-resolution 2D calculations show that the wave train indeed undergoes a significant transformation once the zonal flow along the jet axis is decelerated below the threshold. The subsequent flow evolution depends on the nature of the discontinuity in the basic-state PV. When the discontinuity is entirely due to the vorticity profile, waves are compressed and partially deflected sideways but no complete blocking occurs. When the discontinuity in PV is augmented by the layer thickness variation, the incident wave train is blocked and split into two tracks at the stagnation point, eventually leading to a formation of a modon-like vortex pair, reminiscent of an atmospheric blocking. Implications for low-frequency variability of the atmosphere are discussed.

On the Application of Selected Wave Group Spectra for the Experimental Investigation of Low Frequency Motions of a Moored Structure

2009 ◽  
Author(s):  
Janou Hennig ◽  
Antonio Carlos Fernandes ◽  
Hans Cozijn ◽  
Marcio Maia Domingues
Keyword(s):  
Power Spectrum ◽  
Wave Train ◽  
Power Spectra ◽  
Low Frequency ◽  
Model Tests ◽  
Wave Power ◽  
Wave Group ◽  
Sea State ◽  
Alternative Approach ◽  
First Results

A moored structure shows both wave and low frequency motions in waves. Wave frequency motions are related to the wave elevation and wave power spectrum of the sea state while low frequency motions are driven by wave groups and the corresponding wave group spectrum. Wave power spectra can be calibrated for model tests. The corresponding wave group spectrum follows from the wave power spectrum together with the applied wave seed or phasing of the wave train. Thus, in common practice (both in simulations and model tests), the wave group spectrum follows from the arbitrary choice of a random seed. This can lead to an under- or overestimation of the resulting low frequency motions of the moored object as compared to the theoretical group spectrum. As an alternative approach, the seeds which give the highest and lowest wave group spectra can be applied in the tests. In this paper, first results of model tests with a moored tanker based on an intentional choice of wave group spectra are presented.

scholarly journals Wave and plasma measurements and GPS diagnostics of the main ionospheric trough as a hybrid method used for Space Weather purposes

2008 ◽  
Vol 26 (2) ◽  
pp. 295-304 ◽  
Author(s):  
H. Rothkaehl ◽  
A. Krakowski ◽  
I. Stanislawska ◽  
J. Błęcki ◽  
M. Parrot ◽  
...  
Keyword(s):  
Space Weather ◽  
Acoustic Waves ◽  
Particle Interaction ◽  
Low Frequency ◽  
Wave Activity ◽  
Geomagnetic Disturbances ◽  
Geomagnetic Field Line ◽  
Unique Region ◽  
Main Ionospheric Trough ◽  
Plasma Measurements

Abstract. The region of the main ionospheric trough is a unique region of the ionosphere, where different types of waves and instabilities can be generated. This region of the ionosphere acts like a lens, focusing a variety of indicators from the equator of plasmapause and local ionospheric plasma. This paper reports the results of monitoring the mid-latitude trough structure, dynamics and wave activity. For these purposes, the data gathered by the currently-operating DEMETER satellite and past diagnostics located on IK-19, Apex, and MAGION-3 spacecraft, as well as TEC measurements were used. A global-time varying picture of the ionospheric trough was reconstructed using the sequence of wave spectra registered and plasma measurements in the top-side ionosphere. The authors present the wave activity from ULF frequency band to the HF frequency detected inside the trough region and discuss its properties during geomagnetic disturbances. It is thought that broadband emissions are correlated with low frequency radiation, which is excited by the wave-particle interaction in the equatorial plasmapause and moves to the ionosphere along the geomagnetic field line. In the ionosphere, the suprathermal electrons can interact with these electrostatic waves and excite electron acoustic waves or HF longitudinal plasma waves. Furthermore, the electron density trough can provide useful data on the magnetosphere ionosphere dynamics and morphology and, in consequence, can be used for Space Weather purposes.

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

Understanding the controlling factors of Ultra-Low Frequency waves and their penetration during geomagnetic storms

2020 ◽  
Author(s):  
Jonathan Rae ◽  
Kyle Murphy ◽  
Clare Watt ◽  
Jasmine Sandhu ◽  
Samuel Wharton ◽  
...  
Keyword(s):  
Solar Wind ◽  
Radiation Belt ◽  
Ring Current ◽  
Geomagnetic Storms ◽  
Particle Interaction ◽  
Low Frequency ◽  
Controlling Factors ◽  
Wave Power ◽  
Inner Magnetosphere ◽  
Ulf Wave

&lt;p&gt;Wave-particle interactions play a key role in radiation belt dynamics. Traditionally, Ultra-Low Frequency (ULF) wave-particle interaction is parameterised statistically by a small number of controlling factors for given solar wind driving conditions or geomagnetic activity levels. Here, we investigate solar wind driving of ultra-low frequency (ULF) wave power and the role of the magnetosphere in screening that power from penetrating deep into the inner magnetosphere. We demonstrate that, during enhanced ring current intensity, the Alfv&amp;#233;n continuum plummets, allowing lower frequency waves to penetrate deeper into the magnetosphere than during quiet periods. With this penetration, ULF wave power is able to accumulate closer to the Earth than characterised by statistical models. During periods of enhanced solar wind driving such as coronal mass ejection driven storms, where ring current intensities maximise, the observed penetration provides a simple physics-based reason for why storm-time ULF wave power is different compared to non-storm time waves. We demonstrate statistically that the ring current plays a pivotal role in allowing ULF wave energy to access the inner magnetosphere and show a new parameterisation of ULF wave power for radiation belt research purposes that is specifically tuned for geomagnetic storms.&lt;/p&gt;

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