scholarly journals Chromospheric Heating by MHD Waves and Instabilities

2021 ◽  
Author(s):  
A.K. Srivastava ◽  
J. L. Ballester ◽  
P.S. Cally ◽  
M. Carlsson ◽  
M. Goossens ◽  
...  
Keyword(s):  
Mhd Waves ◽  
Mhd Waves And Instabilities ◽  
Chromospheric Heating

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 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 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 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 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)

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

scholarly journals Pc5 geomagnetic field fluctuations at discrete frequencies at a low latitude station

2001 ◽  
Vol 19 (3) ◽  
pp. 321-325 ◽  
Author(s):  
U. Villante ◽  
P. Francia ◽  
S. Lepidi
Keyword(s):  
Solar Wind ◽  
Geomagnetic Field ◽  
Wind Pressure ◽  
Mhd Waves ◽  
Low Latitude ◽  
Time Intervals ◽  
Latitude Station ◽  
Field Fluctuations ◽  
Mhd Waves And Instabilities ◽  
Solar Wind Pressure

Abstract. A statistical analysis of the geomagnetic field fluctuations in the Pc5 frequency range (1–5 mHz) at a low latitude station (L = 1.6) provides further evidence for daytime power peaks at discrete frequencies. The power enhancements, which become more pronounced during high solar wind pressure conditions, may be interpreted in terms of ground signatures of magnetospheric cavity/waveguide compressional modes driven by solar wind pressure pulses. In this sense, the much clearer statistical evidence for afternoon events can be related to corotating structures mainly impinging the postnoon magnetopause. A comparison with results obtained for the same time intervals from previous investigations at higher latitudes and in the Earth’s magnetosphere confirms the global character of the observed modes.Key words. Magnetospheric physics (MHD waves and instabilities; solar wind-magnetospheric interactions)

scholarly journals A case study of a radially polarized Pc4 event observed by the Equator-S satellite

2000 ◽  
Vol 18 (4) ◽  
pp. 411-415 ◽  
Author(s):  
R. Cramm ◽  
K. H. Glassmeier ◽  
C. Othmer ◽  
K. H. Fornacon ◽  
H. U. Auster ◽  
...  
Keyword(s):  
Analytical Signal ◽  
Alfven Wave ◽  
Wave Number ◽  
Mhd Waves ◽  
Magnetic Field Data ◽  
Line Resonance ◽  
Mhd Waves And Instabilities ◽  
Radially Polarized ◽  
The Magnetic Field

Abstract. A 16 mHz Pc4 pulsation was recorded on March 17, 1998, in the prenoon sector of the Earth's magnetosphere by the Equator-S satellite. The event is strongly localized in radial direction at approximately L = 5 and exhibits properties of a field line resonance such as an ellipticity change as seen by applying the method of the analytical signal to the magnetic field data. The azimuthal wave number was estimated as m \\approx 150. We discuss whether this event can be explained by the FLR mechanism and find out that the change in ellipticity is more a general feature of a localized Alfvén wave than indicative of a resonant process.Key words: Magnetospheric physics (MHD waves and instabilities)

scholarly journals Upstream waves and field line resonances: simultaneous presence and alternation in Pc3 pulsation events

1998 ◽  
Vol 16 (1) ◽  
pp. 34-48 ◽  
Author(s):  
J. Verõ ◽  
H. Lühr ◽  
M. Vellante ◽  
I. Best ◽  
J. Střeštik ◽  
...  
Keyword(s):  
Field Line ◽  
Geomagnetic Field ◽  
Interplanetary Medium ◽  
Mhd Waves ◽  
Field Line Resonance ◽  
Field Line Resonances ◽  
Line Resonance ◽  
Mhd Waves And Instabilities ◽  
Field Lines ◽  
Upstream Waves

Abstract. Based on a detailed study of Pc3 events at an array between L = 1.5 and 3 in Central Europe, the authors found quick changes between upstream waves (UW, i.e. pulsation directly driven by UW) and field line resonance (FLR, i.e. azimuthal oscillations of geomagnetic field lines). The alternation of the two types is especially characteristic (and the UW part stronger) if the interplanetary magnetic field (IMF) is highly variable. Events due to field line resonance may have a structure consisting of multiple lines with frequencies differing by about 10%, corresponding to neighbouring shells of field lines separated by about 100 km at the surface. This coincides with previous findings (about 10% at a meridional distance of 80 km). The frequency of the UW type is well correlated with the frequency of waves in the interplanetary medium. Additionally, there are signals of unidentified origin which also seem to be influenced by IMF.>Key words. Magnetosphere Physics · MHD waves and instabilities · Plasmasphere · Solar wind/magnetosphere interactions

scholarly journals A comparison of EISCAT and HF Doppler observations of a ULF wave

1998 ◽  
Vol 16 (10) ◽  
pp. 1190-1199 ◽  
Author(s):  
D. M. Wright ◽  
T. K. Yeoman ◽  
J. A. Davies
Keyword(s):  
Resonance Region ◽  
Mhd Waves ◽  
Broad Resonance ◽  
Radio Science ◽  
Ionospheric Physics ◽  
Ulf Wave ◽  
Bulk Motion ◽  
First Results ◽  
Mhd Waves And Instabilities ◽  
Uhf Radar

Abstract. Since the middle of 1995, an HF Doppler sounder has been running almost continuously in northern Norway, with the receiver at Ramfjordmoen and the transmitter at Seljelvnes. Concurrent operation of the EISCAT UHF radar in common programme (CP-1) mode has made it possible to study the ionospheric signature of a magnetospheric ULF wave. These are the first results of such wave signatures observed simultaneously in both instruments. It has been demonstrated that the observed Doppler signature was mainly due to the vertical bulk motion of the ionosphere caused by the electric field perturbation of the ULF wave and the first direct observational confirmation of a numerical simulation has been achieved. The wave, which was Alfvénic in nature, was detected by the instruments 8° equatorward of the broad resonance region. The implications for the deduced wave modes in the ionosphere and the mechanism producing the HF Doppler variations are discussed.Key words. Magnetosphere-ionosphere interactions · MHD waves and instabilities · Radio science · Ionospheric physics

Sign in / Sign up

Export Citation Format

Share Document