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 Optical signatures of auroral arcs produced by field line resonances: comparison with satellite observations and modeling

2003 ◽  
Vol 21 (4) ◽  
pp. 933-945 ◽  
Author(s):  
J. C. Samson ◽  
R. Rankin ◽  
V. T. Tikhonchuk
Keyword(s):  
Phase Shift ◽  
Field Line ◽  
Electric Fields ◽  
Low Frequency ◽  
Optical Data ◽  
Field Line Resonance ◽  
Field Line Resonances ◽  
Line Resonance ◽  
Field Lines ◽  
Auroral Arcs

Abstract. We show two examples from the CANOPUS array of the optical signatures of auroral arcs produced by field line resonances on the night of 31 January 1997. The first example occurs during local evening at about 18:00 MLT (Magnetic Local Time), where CANOPUS meridian scanning photometer data show all the classic features of field line resonances. There are two, near-monochromatic resonances (at approximately 2.0 and 2.5 mHz) and both show latitudinal peaks in amplitude with an approximately 180 degree latitudinal phase shift across the maximum. The second field line resonance event occurs closer to local midnight, between approximately 22:00 and 22:40 MLT. Magnetometer and optical data show that the field line resonance has a very low frequency, near 1.3 mHz. All-sky imager data from CANOPUS show that in this event the field line resonances produce auroral arcs with westward propagation, with arc widths of about 10 km. Electron energies are on the order of 1 keV. This event was also seen in data from the FAST satellite (Lotko et al., 1998), and we compare our observations with those of Lotko et al. (1998). A remarkable feature of this field line resonance is that the latitudinal phase shift was substantially greater than 180 degrees. In our discussion, we present a model of field line resonances which accounts for the dominant physical effects and which is in good agreement with the observations. We emphasize three points. First, the low frequency of the field line resonance in the second event is likely due to the stretched topology of the magnetotail field lines, with the field line resonance on field lines threading the earthward edge of the plasma sheet. Second, the latitudinal phase structure may indicate dispersive effects due to electron trapping or finite ion gyroradius. Third, we show that a nonlocal conductivity model can easily explain the parallel electric fields and the precipitating electron energies seen in the field line resonance.Key words. Magnetospheric physics (electric fields; energetic particles precipitating; current systems)

scholarly journals Magnetosonic resonance in a dipole-like magnetosphere

2006 ◽  
Vol 24 (8) ◽  
pp. 2277-2289 ◽  
Author(s):  
A. S. Leonovich ◽  
D. A. Kozlov ◽  
V. A. Pilipenko
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Ring Current ◽  
Effective Interaction ◽  
Field Line Resonance ◽  
Line Resonance ◽  
Field Lines

Abstract. A theory of resonant conversion of fast magnetosonic (FMS) waves into slow magnetosonic (SMS) oscillations in a magnetosphere with dipole-like magnetic field has been constructed. Monochromatic FMS waves are shown to drive standing (along magnetic field lines) SMS oscillations, narrowly localized across magnetic shells. The longitudinal and transverse structures, as well as spectrum of resonant SMS waves are determined. Frequencies of fundamental harmonics of standing SMS waves lie in the range of 0.1–1 mHz, and are about two orders of magnitude lower than frequencies of similar Alfvén field line resonance harmonics. This difference makes an effective interaction between these MHD modes impossible. The amplitude of SMS oscillations rapidly decreases along the field lines from the magnetospheric equator towards the ionosphere. In this context, magnetospheric SMS oscillations cannot be observed on the ground, and the ionosphere does not play any role either in their generation or dissipation. The theory developed can be used to interpret the occurrence of compressional Pc5 waves in a quiet magnetosphere with a weak ring current.

scholarly journals High-latitude dayside ionosphere response to Pc5 field line resonance

2003 ◽  
Vol 21 (7) ◽  
pp. 1509-1520 ◽  
Author(s):  
F. Pitout ◽  
P. Eglitis ◽  
P.-L. Blelly
Keyword(s):  
Electric Field ◽  
Field Line ◽  
High Latitude ◽  
Mhd Waves ◽  
Ion Temperature ◽  
Field Line Resonance ◽  
Temperature Oscillations ◽  
Dayside Magnetopause ◽  
Line Resonance ◽  
Ground Magnetic

Abstract. We report observations of pulsations due to Field Line Resonance (FLR) in the morning sector of the high-latitude dayside ionosphere on 1 February 1998. The Geotail spacecraft, ideally skimming the dayside magnetopause, monitored the magnetopause motion, which is seen to induce a modulated response of the ionosphere by means of ULF waves. Pulsations in the Pc5 frequency range were observed in the ground magnetic field measured by the IMAGE array, as well as in the electron and ion temperatures measured by the EISCAT Svalbard Radar. The ion temperature oscillations are an indicator of a modulated convection electric field while field-aligned currents (FAC) associated with the FLR control the electron temperature. We have performed a simulation of the ionosphere experiencing sinusoidal FAC and electric field in order to confirm our hypothesis. In addition to the ionospheric response, the possible cause of the FLR and processes involved are also discussed.Key words. Magnetospheric physics (MHD waves and instabilities; magnetosphere-ionosphere interactions) – Ionosphere (polar ionosphere)

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