scholarly journals A slow mode wave as a possible source of Pi 2 and associated particle precipitation: a case study

1999 ◽  
Vol 17 (5) ◽  
pp. 674-681 ◽  
Author(s):  
O. Saka ◽  
O. Watanabe ◽  
K. Okada ◽  
D. N. Baker
Keyword(s):  
Mhd Waves ◽  
Wave Form ◽  
Fluxgate Magnetometer ◽  
Syowa Station ◽  
Low Energy Electrons ◽  
Dip Equator ◽  
Substorm Activity ◽  
Mhd Waves And Instabilities ◽  
Break Up ◽  
Auroral Phenomena

Abstract. An intensification of auroral luminosity referred to as an auroral break-up often accompanies the onset of geomagnetic pulsation (Pi 2) at the dip-equator. One such auroral break-up occurred at 2239 UT on 16 June, 1986, being accompanied by weak substorm activity (AE~50 nT) which was recorded in all-sky image of Syowa Station, Antarctica (66.2°S, 71.8°E in geomagnetic coordinates). The associated Pi 2 magnetic pulsation was detected by a fluxgate magnetometer in the afternoon sector 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). In spite of the large separation of the two stations in longitude and latitude, the auroral break-up and subsequent luminosity modulation were seen to be correlated with the wave form of the ground Pi 2 pulsation. This occurred in such a way that the luminosity maximum was seen to occur at the phase of maximum amplitudes of Pi 2 wave form. We argue that the observed correlation could be interpreted as indicating a Pi 2-modulation of a field-aligned acceleration of the low energy electrons that may occur near the equator of the midnight magnetosphere.Key words. Magnetospheric physics (auroral phenomena; energetic particles · precipitating; MHD waves and instabilities)

scholarly journals Case studies on the dynamics of Pi3 geomagnetic and riometer pulsations during auroral activations

2002 ◽  
Vol 20 (2) ◽  
pp. 151-159 ◽  
Author(s):  
N. G. Kleimenova ◽  
O. V. Kozyreva ◽  
K. Kauristie ◽  
J. Manninen ◽  
A. Ranta
Keyword(s):  
Mhd Waves ◽  
Geomagnetic Pulsations ◽  
Tight Coupling ◽  
Ionospheric Currents ◽  
Particle Precipitation ◽  
Mhd Waves And Instabilities ◽  
Energetic Particle Precipitation ◽  
Particle Intensity ◽  
Auroral Phenomena ◽  
Current Signatures

Abstract. A sequence of three subsequent auroral activations (at 18:10, 19:48 and 20:00 UT) on 9 February 1997 is analysed. The brightenings of optical auroras were collocated with latitudinally localized bursts of pulsating riometer absorption and Pi3 geomagnetic pulsations. In two of the cases, the strongest westward directed electrojet currents and the footpoint of the upward directed field-aligned currents related to the auroral brightening were observed in the same region as the largest amplitude of the pulsations and their polarization changed. In the third case, field-aligned current signatures were present, but not so pronounced that their accurate location could not be defined. In all cases, the spectra of geomagnetic and absorption pulsations were similar. Based on ground-based observations alone, it is difficult to say whether the energetic particle precipitation (riometer absorption) was modulated by the geomagnetic pulsations or whether the geomagnetic pulsations were caused by varying ionospheric currents controlled by the precipitating particle intensity. However, the localized nature of both pulsations of the two different phenomena and their tight coupling with each other seem to support the latter option.Key words. Ionosphere (Particle precipitation) – Magnetospheric physics (auroral phenomena; MHD 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 Compressional Pc5 type pulsations in the morningside plasma sheet

2001 ◽  
Vol 19 (3) ◽  
pp. 311-320 ◽  
Author(s):  
A. Vaivads ◽  
W. Baumjohann ◽  
G. Haerendel ◽  
R. Nakamura ◽  
H. Kucharek ◽  
...  
Keyword(s):  
Phase Velocity ◽  
Plasma Sheet ◽  
Mhd Waves ◽  
Plasma Velocity ◽  
Frequency Range ◽  
Magnetospheric Configuration And Dynamics ◽  
Substorm Activity ◽  
Mhd Waves And Instabilities ◽  
Magnetospheric Configuration ◽  
Generation Mechanisms

Abstract. We study compressional pulsations in Pc5 frequency range observed in the dawn-side at distances of about 10 RE , close to the magnetic equator. We use data obtained during two events of conjunctions between Equator-S and Geotail: 1000–1700 UT on 9 March 1998, and 0200–0600 UT on 25 April 1998. In both events, pulsations are observed after substorm activity. The pulsations are antisymmetric with respect to the equatorial plane (even mode), and move eastward with phase velocity close to plasma velocity. The pulsations tend to be pressure balanced. We also discuss possible generation mechanisms of the pulsations.Key words. Magnetospheric physics (magnetospheric configuration and dynamics; MHD waves and instabilities; plasma sheet)

scholarly journals Cluster as a wave telescope – first results from the fluxgate magnetometer

2001 ◽  
Vol 19 (10/12) ◽  
pp. 1439-1447 ◽  
Author(s):  
K.-H. Glassmeier ◽  
U. Motschmann ◽  
M. Dunlop ◽  
A. Balogh ◽  
M. H. Acuña ◽  
...  
Keyword(s):  
Wave Vector ◽  
Low Frequency ◽  
Plasma Waves ◽  
Minimum Variance ◽  
Mhd Waves ◽  
Fluxgate Magnetometer ◽  
Propagating Waves ◽  
First Results ◽  
Mhd Waves And Instabilities ◽  
First Time

Abstract. The four Cluster spacecraft provide an excellent opportunity to study spatial structures in the magnetosphere and adjacent regions. Propagating waves are amongst the interesting structures and for the first time, Cluster will allow one to measure the wave vector of low-frequency fluctuations in a space plasma. Based on a generalized minimum variance analysis wave vector estimates will be determined in the terrestrial magnetosheath and the near-Earth solar wind. The virtue and weakness of the wave telescope technique used is discussed in detail.Key words. Electromagnetics (wave propagation) – Magnetospheric physics (MHD waves and instabilities; plasma waves and instabilities)

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 Simultaneous optical, CUTLASS HF radar, and FAST spacecraft observations: signatures of boundary layer processes in the cusp

2004 ◽  
Vol 22 (2) ◽  
pp. 511-525 ◽  
Author(s):  
K. Oksavik ◽  
F. Søraas ◽  
J. Moen ◽  
R. Pfaff ◽  
J. A. Davies ◽  
...  
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Broad Band ◽  
Spectral Width ◽  
Hf Radar ◽  
Optical Data ◽  
Low Energy Electrons ◽  
Field Lines ◽  
Auroral Phenomena ◽  
Electric Fields And Currents

Abstract. In this paper we discuss counterstreaming electrons, electric field turbulence, HF radar spectral width enhancements, and field-aligned currents in the southward IMF cusp region. Electric field and particle observations from the FAST spacecraft are compared with CUTLASS Finland spectral width enhancements and ground-based optical data from Svalbard during a meridional crossing of the cusp. The observed 630nm rayed arc (Type-1 cusp aurora) is associated with stepped cusp ion signatures. Simultaneous counterstreaming low-energy electrons on open magnetic field lines lead us to propose that such electrons may be an important source for rayed red arcs through pitch angle scattering in collisions with the upper atmosphere. The observed particle precipitation and electric field turbulence are found to be nearly collocated with the equatorward edge of the optical cusp, in a region where CUTLASS Finland also observed enhanced spectral width. The electric field turbulence is observed to extend far poleward of the optical cusp. The broad-band electric field turbulence corresponds to spatial scale lengths down to 5m. Therefore, we suggest that electric field irregularities are directly responsible for the formation of HF radar backscatter targets and may also explain the observed wide spectra. FAST also encountered two narrow highly structured field-aligned current pairs flowing near the edges of cusp ion steps. Key words. Ionosphere (electric fields and currents). Magnetosphere physics (magnetopause, cusp, and boundary layers; auroral phenomena)

scholarly journals Post-noon two-minute period pulsating aurora and their relationship to the dayside convection pattern

1999 ◽  
Vol 17 (7) ◽  
pp. 877-891 ◽  
Author(s):  
S. E. Milan ◽  
T. K. Yeoman ◽  
M. Lester ◽  
J. Moen ◽  
P. E. Sandholt
Keyword(s):  
Current System ◽  
Wave Activity ◽  
Mhd Waves ◽  
Magnetohydrodynamic Wave ◽  
Auroral Emission ◽  
Minute Period ◽  
Optical Signature ◽  
Short Period ◽  
Auroral Emissions ◽  
Auroral Phenomena

Abstract. Poleward-moving auroral forms, as observed by meridian-scanning photometers, in the vicinity of the cusp region are generally assumed to be the optical signature of flux transfer events. Another class of quasi-continuous, short period (1-2 min) wave-like auroral emission has been identified, closely co-located with the convection reversal boundary in the post-noon sector, which is similar in appearance to such cusp aurora. It is suggested that these short period wave-like auroral emissions, the optical signature of boundary plasma sheet precipitation in the region 1 field-aligned current system, are associated with ULF magnetohydrodynamic wave activity, which is observed simultaneously by ground magnetometer stations. This association with ULF wave activity is strengthened by the observation of several harmonic frequencies in the pulsation spectrum, each an overtone of the fundamental standing wave resonance frequency.Key words. Magnetospheric physics (auroral phenomena; magnetopause · cusp · and boundary layers; MHD waves and instabilities)

scholarly journals Waveform and packet structure of lion roars

1999 ◽  
Vol 17 (12) ◽  
pp. 1528-1534 ◽  
Author(s):  
W. Baumjohann ◽  
R. A. Treumann ◽  
E. Georgescu ◽  
G. Haerendel ◽  
K.-H. Fornacon ◽  
...  
Keyword(s):  
Sampling Rate ◽  
Cone Angle ◽  
Mhd Waves ◽  
Lower Hybrid ◽  
Fluxgate Magnetometer ◽  
High Sampling Rate ◽  
Polarized Waves ◽  
Interplanetary Physics ◽  
Electron Gyrofrequency ◽  
First Time

Abstract. The Equator-S magnetometer is very sensitive and has a sampling rate of normally 128 Hz. The high sampling rate allows for the first time fluxgate magnetometer measurements of ELF waves between the ion cyclotron and the lower hybrid frequencies in the equatorial dayside magnetosheath. The so-called lion roars, typically seen by the Equator-S magnetometer at the bottom of the magnetic troughs of magnetosheath mirror waves, are near-monochromatic packets of electron whistler waves lasting for a few wave cycles only, typically 0.25 s. They are right-hand circularly polarized waves with typical amplitudes of 0.5–1 nT at around one tenth of the electron gyrofrequency. The cone angle between wave vector and ambient field is usually smaller than 1.5°.Key words. Interplanetary physics (MHD waves and turbulence; plasma waves and turbulence)

scholarly journals ULF wave occurrence statistics in a high-latitude HF Doppler sounder

1999 ◽  
Vol 17 (6) ◽  
pp. 749-758 ◽  
Author(s):  
D. M. Wright ◽  
T. K. Yeoman ◽  
T. B. Jones
Keyword(s):  
Solar Cycle ◽  
Geomagnetic Activity ◽  
High Latitude ◽  
Statistical Study ◽  
Low Frequency ◽  
Occurrence Rate ◽  
Mhd Waves ◽  
Ulf Wave ◽  
High Latitude Ionosphere ◽  
Mhd Waves And Instabilities

Abstract. Ultra low frequency (ULF) wave activity in the high-latitude ionosphere has been observed by a high frequency (HF) Doppler sounder located at Tromsø, Norway (69.7°N, 19.2°E geographic coordinates). A statistical study of the occurrence of these waves has been undertaken from data collected between 1979 and 1984. The diurnal, seasonal, solar cycle and geomagnetic activity variations in occurrence have been investigated. The findings demonstrate that the ability of the sounder to detect ULF wave signatures maximises at the equinoxes and that there is a peak in occurrence in the morning sector. The occurrence rate is fairly insensitive to changes associated with the solar cycle but increases with the level of geomagnetic activity. As a result, it has been possible to characterise the way in which prevailing ionospheric and magnetospheric conditions affect such observations of ULF waves.Key words. Ionosphere (auroral ionosphere; ionosphere -magnetosphere interactions) · Magnetospheric physics (MHD waves and instabilities)

scholarly journals Penetration of magnetosonic waves into the magnetosphere: influence of a transition layer

2003 ◽  
Vol 21 (5) ◽  
pp. 1083-1093 ◽  
Author(s):  
A. S. Leonovich ◽  
V. V. Mishin ◽  
J. B. Cao
Keyword(s):  
Solar Wind ◽  
Energy Flux ◽  
Transition Layer ◽  
External Source ◽  
Mhd Waves ◽  
Time Interval ◽  
Total Energy Input ◽  
Mhd Waves And Instabilities ◽  
The Waves ◽  
Stratified Model

Abstract. We have constructed a theory for the penetration of magnetosonic waves from the solar wind into the magnetosphere through a transition layer in a plane-stratified model for the medium. In this model the boundary layer is treated as a region, inside of which the parameters of the medium vary from values characteristic for the magnetosphere, to values typical of the solar wind. It is shown that if such a layer has sufficiently sharp boundaries, then magnetosonic eigen-oscillations can be excited inside of it. The boundaries of such a layer are partially permeable for magnetosonic waves. Therefore, if the eigen-oscillations are not sustained by an external source, they will be attenuated, because some of the energy is carried away by the oscillations that penetrate the solar wind and the magnetosphere. It is shown that about 40% of the energy flux of the waves incident on the transition layer in the magnetotail region penetrate to the magnetosphere’s interior. This energy flux suffices to sustain the stationary convection of magnetospheric plasma. The total energy input to the magnetosphere during a time interval of the order of the substorm growth phase time is comparable with the energetics of an average substorm.Key words. Magnetospheric physics (MHD waves and instabilities; solar wind–magnetosphere interactions) – Space plasma physics (kinetic and MHD theory)

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