scholarly journals A study of Pc-5 ULF oscillations

2004 ◽  
Vol 22 (1) ◽  
pp. 289-302 ◽  
Author(s):  
M. K. Hudson ◽  
R. E. Denton ◽  
M. R. Lessard ◽  
E. G. Miftakhova ◽  
R. R. Anderson
Keyword(s):  
Radiation Effects ◽  
Dominant Mode ◽  
Mhd Waves ◽  
Azimuthal Mode ◽  
Magnetospheric Configuration And Dynamics ◽  
Sudden Commencements ◽  
Magnetic Pulsations ◽  
Pulsation Activity ◽  
Using Data ◽  
Three Components

Abstract. A study of Pc-5 magnetic pulsations using data from the Combined Release and Radiation Effects Satellite (CRRES) was carried out. Three-component dynamic magnetic field spectrograms have been used to survey ULF pulsation activity for the approximate fourteen month lifetime of CRRES. Two-hour panels of dynamic spectra were examined to find events which fall into two basic categories: 1) toroidal modes (fundamental and harmonic resonances) and 2) poloidal modes, which include compressional oscillations. The occurence rates were determined as a function of L value and local time. The main result is a comparable probability of occurence of toroidal mode oscillations on the dawn and dusk sides of the magnetosphere inside geosynchronous orbit, while poloidal mode oscillations occur predominantly along the dusk side, consistent with high azimuthal mode number excitation by ring current ions. Pc-5 pulsations following Storm Sudden Commencements (SSCs) were examined separately. The spatial distribution of modes for the SSC events was consistent with the statistical study for the lifetime of CRRES. The toroidal fundamental (and harmonic) resonances are the dominant mode seen on the dawn-side of the magnetosphere following SSCs. Power is mixed in all three components. In the 21 dusk side SSC events there were only a few examples of purely compressional (two) or radial (one) power in the CRRES study, a few more examples of purely toroidal modes (six), with all three components predominant in about half (ten) of the events. Key words. Magnetospheric physics (MHD waves and instabilities; magnetospheric configuration and dynamics) – Space plasma physics (waves and instabilities)

scholarly journals Connections between whistlers and pulsation activity

2000 ◽  
Vol 18 (8) ◽  
pp. 866-873 ◽  
Author(s):  
J. Verö ◽  
B. Zieger ◽  
J. Szendröi ◽  
M. Vellante ◽  
J. Střesğtik ◽  
...  
Keyword(s):  
Wave Propagation ◽  
Time Scales ◽  
Geomagnetic Pulsation ◽  
Lower Latitude ◽  
Mhd Waves ◽  
Magnetospheric Configuration And Dynamics ◽  
Mhd Waves And Instabilities ◽  
L Value ◽  
Magnetospheric Configuration ◽  
Pulsation Activity

Abstract. Simultaneous whistler records of one station and geomagnetic pulsation (Pc3) records at three stations were compared. In a previous study correlation was found between occurrence and L value of propagation/excitation for the two phenomena. The recently investigated simultaneous records have shown that the correlation is better on longer time scales (days) than on shorter ones (minutes), but the L values of the propagation of whistlers/excitation of pulsations are correlated, i.e. if whistlers propagate in higher latitude ducts, pulsations have periods longer than in the case when whistlers propagate in lower latitude ducts.Key words: Electromagnetics (wave propagation) - Magnetospheric physics (magnetospheric configuration and dynamics; MHD waves and instabilities)

scholarly journals What we talk about when we talk about interactivity: Empowerment in public discourse

2016 ◽  
Vol 19 (7) ◽  
pp. 1052-1071 ◽  
Author(s):  
Marguerite Barry ◽  
Gavin Doherty
Keyword(s):  
Digital Media ◽  
Public Discourse ◽  
Data Access ◽  
Dominant Mode ◽  
Newspaper Coverage ◽  
Flexible Approach ◽  
Communication Events ◽  
Action Context ◽  
Media Research ◽  
Using Data

This study offers new insights into interactivity by examining its association with empowerment in public discourse. Using data from 20 years of newspaper coverage, a mixed methods analysis reveals different ‘modes’ of interactivity in discourse. Empowerment is the dominant mode of interactivity despite substantial changes in technologies and uses over this time. A content analysis shows that older discourses associate interactivity with specific technologies, while recent discourses use more universal terms. The discourse analysis illustrates the range of empowerment found in different interactive experiences, from basic data access to collaboration across communities, even reaching beyond communication events. The study offers a new model for understanding interactivity and empowerment based on the potential in communications for action, context, strategies and outcomes. This layered and flexible approach has appeal for digital media research and production.

scholarly journals Magnetic turbulence and particle dynamics in the Earth’s magnetotail

2003 ◽  
Vol 21 (9) ◽  
pp. 1947-1953 ◽  
Author(s):  
G. Zimbardo ◽  
A. Greco ◽  
A. L. Taktakishvili ◽  
P. Veltri ◽  
L. M. Zelenyi
Keyword(s):  
Magnetic Field ◽  
Current Sheet ◽  
Sheet Thickness ◽  
Particle Dynamics ◽  
Particle Simulation ◽  
Mhd Waves ◽  
Magnetic Fluctuations ◽  
Magnetic Turbulence ◽  
Magnetospheric Configuration And Dynamics ◽  
Interplanetary Physics

Abstract. The influence of magnetic turbulence in the near-Earth magnetotail on ion motion is investigated by numerical simulation. The magnetotail current sheet is modelled as a magnetic field reversal with a normal magnetic field com-ponent Bn , plus a three-dimensional spectrum of magnetic fluctuations dB which represents the observed magnetic turbulence. The dawn-dusk electric field Ey is also considered. A test particle simulation is performed using different values of Bn and of the fluctuation level dB/B0. We show that when the magnetic fluctuations are taken into account, the particle dynamics is deeply affected, giving rise to an increase in the cross tail transport, ion heating, and current sheet thickness. For strong enough turbulence, the current splits in two layers, in agreement with recent Cluster observations.Key words. Magnetospheric physics (magnetospheric configuration and dynamics) – Interplanetary physics (MHD waves and turbulence) – Electromagnetics (numerical methods)

scholarly journals Magnetospheric lion roars

2000 ◽  
Vol 18 (4) ◽  
pp. 406-410 ◽  
Author(s):  
W. Baumjohann ◽  
E. Georgescu ◽  
K.-H. Fornacon ◽  
H. U. Auster ◽  
R. A. Treumann ◽  
...  
Keyword(s):  
Sampling Rate ◽  
Cone Angle ◽  
Mhd Waves ◽  
Lower Hybrid ◽  
High Sampling Rate ◽  
Polarized Waves ◽  
Magnetospheric Configuration And Dynamics ◽  
Mhd Waves And Instabilities ◽  
Electron Gyrofrequency ◽  
First Time

Abstract. The Equator-S magnetometer is very sensitive and has a sampling rate normally of 128 Hz. The high sampling rate for the first time allows detection of ELF waves between the ion cyclotron and the lower hybrid frequencies in the equatorial dawnside magnetosphere. The characteristics of these waves are virtually identical to the lion roars typically seen at the bottom of the magnetic troughs of magnetosheath mirror waves. The magnetospheric lion roars are near-monochromatic packets of electron whistler waves lasting for a few wave cycles only, typically 0.2 s. They are right-hand circularly polarized waves with typical amplitudes of 0.5 nT at around one tenth of the electron gyrofrequency. The cone angle between wave vector and ambient field is nearly always smaller than 1°.Key words: Magnetospheric physics (magnetospheric configuration and dynamics; MHD waves and instabilities; plasma waves and instabilities)

scholarly journals An initial response of magnetic fields at geosynchronous orbit to Pi 2 onset as observed from the dip-equator

1998 ◽  
Vol 16 (5) ◽  
pp. 542-548 ◽  
Author(s):  
O. Saka ◽  
H. Akaki ◽  
O. Watanabe ◽  
M. Shinohara ◽  
D. N. Baker
Keyword(s):  
Field Line ◽  
International Study ◽  
Initial Response ◽  
Mhd Waves ◽  
Meridional Plane ◽  
Fluxgate Magnetometer ◽  
Magnetospheric Configuration And Dynamics ◽  
Magnetometer Data ◽  
Dip Equator ◽  
Field Lines

Abstract. Fluxgate magnetometer data recorded at the dip-equator (Huancayo, Peru; 1.44°N, 355.9° in geomagnetic coordinates; 12.1°S, 75.2°W in geographic coordinates; L = 1.00) with higher accuracy of timing (0.1 s) and amplitude resolution (0.01 nT) were utilized to survey an onset of Pi 2 pulsations in the midnight sector (2100–0100 LT) during PROMIS (Polar Region and Outer Magnetosphere International Study) periods (1 March–20 June, 1986). It is found that changing field line magnitude and vector as observed by magnetometer on board the synchronous satellites in the midnight sector often takes place simultaneously with the onset of Pi 2 pulsations at the dip-equator. The field disturbances that follow thereafter tend to last for some time both at the geosynchronous altitudes and the dip-equator. In this report, we examine the initial response of the field lines in space, and attempt to classify how the field line vector changed in the meridional plane. Key words. Magnetospheric physics · Magnetospheric configuration and dynamics · MHD waves and instabilities · Plasmasphere

scholarly journals Ground-based and satellite observations of high-latitude auroral activity in the dusk sector of the auroral oval

2001 ◽  
Vol 19 (10/12) ◽  
pp. 1683-1696 ◽  
Author(s):  
K. Kauristie ◽  
T. I. Pulkkinen ◽  
O. Amm ◽  
A. Viljanen ◽  
M. Syrjäsuo ◽  
...  
Keyword(s):  
Solar Wind ◽  
High Latitude ◽  
Auroral Oval ◽  
Outer Edge ◽  
Satellite Observations ◽  
Mhd Waves ◽  
Clear Correlation ◽  
Close Relationship ◽  
Magnetic Pulsations ◽  
Dusk Sector

Abstract. On 7 December 2000, during 13:30–15:30 UT the MIRACLE all-sky camera at Ny Ålesund observed auroras at high-latitudes (MLAT ~ 76) simultaneously when the Cluster spacecraft were skimming the magnetopause in the same MLT sector (at ~ 16:00–18:00 MLT). The location of the auroras (near the ionospheric convection reversal boundary) and the clear correlation between their dynamics and IMF variations suggests their close relationship with R1 currents. Consequently, we can assume that the Cluster spacecraft were making observations in the magnetospheric region associated with the auroras, although exact magnetic conjugacy between the ground-based and satellite observations did not exist. The solar wind variations appeared to control both the behaviour of the auroras and the magnetopause dynamics. Auroral structures were observed at Ny Ålesund especially during periods of negative IMF BZ. In addition, the Cluster spacecraft experienced periodic (T ~ 4 - 6 min) encounters between magnetospheric and magnetosheath plasmas. These undulations of the boundary can be interpreted as a consequence of tailward propagating magnetopause surface waves. Simultaneous dusk sector ground-based observations show weak, but discernible magnetic pulsations (Pc 5) and occasionally periodic variations (T ~ 2 - 3 min) in the high-latitude auroras. In the dusk sector, Pc 5 activity was stronger and had characteristics that were consistent with a field line resonance type of activity. When IMF BZ stayed positive for a longer period, the auroras were dimmer and the spacecraft stayed at the outer edge of the magnetopause where they observed electromagnetic pulsations with T ~ 1 min. We find these observations interesting especially from the viewpoint of previously presented studies relating poleward-moving high-latitude auroras with pulsation activity and MHD waves propagating at the magnetospheric boundary layers.Key words. Ionosphere (ionosphere-magnetosphere interaction) – Magnetospheric physics (auroral phenomena; solar wind – magnetosphere interactions)

scholarly journals Interaction of Pc4 ULF waves with solar wind velocity and its dependence on Kp values

2021 ◽  
Vol 14 (12) ◽  
pp. 1013-1020
Author(s):  
M T Khan ◽  
◽  
K A Nafees ◽  
A K Singh
Keyword(s):  
Solar Wind ◽  
Solar Wind Speed ◽  
Mhd Waves ◽  
Ulf Waves ◽  
Ulf Wave ◽  
Magnetic Pulsations ◽  
Recorded Data ◽  
Mhd Waves And Instabilities ◽  
Field Lines ◽  
East West

Background/Objectives: Magnetic Pulsations recorded on the ground in the earth are produced by processes inside the magnetosphere and solar wind. These processes produce a wide variety of ULF hydromagnetic wave type which can be categorized on the ground as either Pi or Pc pulsations (irregular or continuous). Methods: Distinctive regions of the magnetosphere originate different frequencies of waves. Digital Dynamic Spectra (DDS) for the northsouth (X), east-west (Y) and vertical (Z) components of the recorded data were constructed for every day for 365 days (January 1 to December 31, 2005) in the station order PON, HAN and NAG respectively. Pc4 geomagnetic pulsations are quasi-sinusoidal fluctuations in the earth’s magnetic field in the length range 45-150 seconds. The magnitude of these pulsations ranges from fraction of a Nano Tesla (nT) to several nT. The monthly variation of Pc4 occurrence has a Kp dependence range of 0 to 9-. However, Pc4 occurrence was reported for Kp values, yet the major Pc4 events occurred for rage 5+ <Kp< 8+. The magnitudes of intervals of Pc4 occurrence decreased in the station order PON, HAN and NAG respectively. Analysis of the data for the whole year 2005 provided similar patterns of Pc4 occurrence for Vsw at all the three stations. Although Pc4 ULF wave occurrence become reported for Vsw ranging from 250 to 1000 Km/s, yet the major Pc4 event recorded for a Vsw range of 300-700 Km/sec. Findings: The current study is undertaken for describing the interaction of Pc4 ULF waves with solar wind speed and its dependence on Kp values. The results suggest that the solar wind control Pc4 occurrence through a mechanism in which Pc4 wave energy is convected through the magnetosheath and coupled to the standing oscillations of the magnetospheric field lines. PACS Nos: 94.30.cq; 96.50.Tf Keywords: Geomagnetic micropulsations; MHD waves and instabilities; Solar wind-control of Pc4 pulsation

Relations of field line resonances and upstream waves and the winter attenuation of pulsations

1995 ◽  
Vol 13 (7) ◽  
pp. 689-697 ◽  
Author(s):  
J. Verő ◽  
I. Best ◽  
M. Vellante ◽  
H. Lühr ◽  
M. de Lauretis ◽  
...  
Keyword(s):  
Field Line ◽  
Solar Maximum ◽  
Occurrence Frequency ◽  
Geomagnetic Pulsations ◽  
Field Line Resonances ◽  
Line Resonance ◽  
Northern Winter ◽  
Pulsation Activity ◽  
Using Data ◽  
Upstream Waves

Abstract. Using data on the occurrence frequency of geomagnetic pulsations of different periods from three observatories in Central Europe, conclusions are drawn about the occurrence of field line resonances and pulsations directly driven by upstream waves at L-values below 3. It was found that both types occur during the interval studied (first 6 months of the year 1991), but both the occurrence frequency of the two types and the characteristic period of the field line resonance change significantly as compared to other intervals. During Northern winter, pulsation activity is severely damped in solar maximum years, including the year 1991. The decrease in the activity of the pulsations is more significant at shorter periods.

scholarly journals G-IRAE: a Generalised approach for linking the total Impact of invasion to species' Range, Abundance and per-unit Effects

2021 ◽  
Author(s):  
Guillaume Latombe ◽  
Jane A Catford ◽  
Franz Essl ◽  
Bernd Lenzner ◽  
David M Richardson ◽  
...  
Keyword(s):  
Plant Invasions ◽  
Practical Method ◽  
Range Size ◽  
Specific Method ◽  
Using Data ◽  
Species Specific ◽  
The Impact ◽  
The Relationship ◽  
Total Impact ◽  
Three Components

The total impact of an alien species was conceptualised as the product of its range size, local abundance and per-unit effect in a seminal paper by Parker and colleagues in 1999, but a practical approach for estimating the three components has been lacking. Here, we generalise the impact formula and, through use of regression models, estimate the relationship between the three components of impact, an approach we term G-IRAE (Generalised Impact - Range size - Abundance - per-unit Effect). Moreover, we show that G-IRAE can also be applied to damage and management costs. We propose two methods for applying G-IRAE. The species-specific method computes the relationship for a given species across multiple invaded sites or regions, assuming a constant per-unit effect across the invaded area. The multi-species method combines data from multiple species across multiple sites or regions to calculate a per-unit effect for each species. While the species-specific method is more accurate, it requires a large amount of data for each species. The multi-species method is more easily applicable and data-parsimonious. We illustrate the multi-species method using data about money spent managing plant invasions in different biomes of South Africa. We found clear differences between species in terms of money spent per unit area invaded, with per-unit expenditures varying substantially between biomes for some species. G-IRAE offers a versatile and practical method which can be applied to many different types of data, to better understand and manage invasions.

Sign in / Sign up

Export Citation Format

Share Document