An explanation of the observation of whistler-mode chorus emissions at the Indian Antarctic station, Maitri (L=4.5)
TL;DR: In this article, a nonlinear growth mechanism was proposed to explain the observed dynamic spectra of whistler-mode chorus emissions, and the frequency sweep rate of chorus emission was computed and compared with that of experimentally observed values, which in general shows good agreement.
Abstract: Observation of whistler-mode chorus emissions recorded at the Indian Antarctic station, Maitri (lat=70°46'S, long=11°50'E, L=4.5), during a quiet period on 5 February 2001 has been reported. The detailed spectral analysis of recorded chorus emissions shows that each chorus element originates from the upper edge of the underlying hiss band. To explain the observed dynamic spectra of these chorus emissions, a possible generation mechanism is presented based on the recent nonlinear theory. It is observed that the seeds of chorus emissions with rising frequency are generated near the magnetic equator as a result of a nonlinear growth mechanism that depends on the wave amplitude. On the basis of this theory, the frequency sweep rate of chorus emission is computed and compared with that of our experimentally observed values, which in general shows good agreement.
Citations
More filters
TL;DR: In this article, the spectral analysis of recorded chorus emissions shows that each chorus element originates from the upper edge of the underlying hiss band, which is the most common form of very low frequency (VLF) emissions in the Earth's magnetosphere.
Abstract: Chorus emissions are the most common form of very low frequency (VLF) emissions in the Earth’s magnetosphere which typically consist of a series of rising tones generated near the magnetic equator, excited by energetic electrons injected into the inner magnetosphere. In the present study, observation of chorus emissions recorded at Indian low latitude ground station Jammu (geomag. lat., 19 26 N; L = 1.17) during a geomagnetic quiet period on 24 February, 1999 is reported. The spectral analysis of recorded chorus emissions shows that each chorus element originates from the upper edge of the underlying hiss band. The observed mean chorus element parameters are as follows: lower band frequency fmin = 1.2 kHz, upper band frequency fUB = 1.96 kHz, frequency sweep rate df/dt = 1.14 kHz/s and repetition period T = 2.5 s. To explain the observed dynamic spectra of these chorus emissions, a possible generation mechanism is presented based on the recent nonlinear theory. It is observed that the seeds of chorus emissions grow from the saturation level of the whistler-mode instability at the equator and then propagate away from the equator as a result of a nonlinear growth mechanism that depends on the wave amplitude. On the basis of this theory, frequency sweep rate of chorus emission is computed and compared with that of our experimentally observed values, which shows, in general, a good agreement.
1 citations
Cites background from "An explanation of the observation o..."
...Singh et al. (2010) applied successfully the nonlinear theory of Omura et al. (2008) to explain the observation of whistler-mode chorus emissions recorded at the Indian Antarctic station, Maitri (lat = 700 46/ S, long = 110 50/ E, L = 4.5), during a quiet period on 5 February, 2001....
[...]
...Generation Mechanism A number of studies have been done to know the process governing the mechanism of chorus emissions (Helliwell, 1967; Omura and Matsumoto, 1982; Trakhtengerts, 1999; Singh and Ronnmark, 2004; Katoh and Omura, 2007; Omura et al., 2008; Singh et al., 2010)....
[...]
...chorus emissions (Helliwell, 1967; Omura and Matsumoto, 1982; Trakhtengerts, 1999; Singh and Ronnmark, 2004; Katoh and Omura, 2007; Omura et al., 2008; Singh et al., 2010)....
[...]
...Singh et al. (2010) successfully applied the nonlinear theory to explain the observation of whistler-mode chorus emissions recorded at the Indian Antarctic station, Maitri during a quiet period on 5 February, 2001....
[...]
TL;DR: In this article, the spectral analysis of the observed discrete very low-frequency emissions consisting of risers, fallers, hooks and oscillating tones has been presented to explain the observed dynamic spectra of the discrete chorus emissions.
Abstract: During the routine analysis of recorded very low-frequency data during the period November, 2012 to February, 2013, at an Indian low-latitude ground station Srinagar (geomag. lat., 24°10′N; L = 1.28), we observed some interesting discrete emissions during quiet period on February 5, 2013, which has been presented in the present study. The spectral analysis of the observed discrete very low-frequency emissions consisting of risers, fallers, hooks and oscillating tones has been presented. To explain the observed dynamic spectra of the discrete chorus emissions, a possible generation mechanism has been presented based on the recent nonlinear theory. On the basis of this theory, frequency sweep rate of discrete chorus emissions has been computed and compared with those of our experimentally observed values.
References
More filters
TL;DR: In this paper, an empirical model of equatorial electron density in the magnetosphere covering the L range 2.25-8.9043 was presented for application to the local time interval 00-15 MLT, and a way to extend the model to the 15-24 MLT period is presented.
Abstract: Attention is given to an empirical model of equatorial electron density in the magnetosphere covering the L range 2.25-8. Although the model is primarily intended for application to the local time interval 00-15 MLT, a way to extend the model to the 15-24-MLT period is presented. The model describes, in piecewise fashion, the 'saturated' plasmasphere, the region of steep plasmapause gradients, and the plasma trough. Within the plasmasphere the model profile can be expressed as logne - Sigma-xi, where x1 = -0.3145L + 3.9043 is the principal or 'reference' term, and additional terms account for: a solar cycle variation with a peak at solar maximum; an annual variation with a December maximum; and a semiannual variation with equinoctial maxima.
787 citations
TL;DR: In this paper, the post-midnight chorus was detected in the midnight sector of the magnetosphere in conjunction with magnetospheric substorms and the characteristics of these emissions such as their frequency time structure, emission frequency with respect to the local equatorial electron gyrofrequency, intensity-time variation, and the average intensity were investigated.
Abstract: The ELF emissions were detected in the midnight sector of the magnetosphere in conjunction with magnetospheric substorms. The emissions were observed at local midnight and early morning hours and are accordingly called 'post-midnight chorus.' The characteristics of these emissions such as their frequency time structure, emission frequency with respect to the local equatorial electron gyrofrequency, intensity-time variation, and the average intensity were investigated. The occurrence of the chorus in the nightside magnetosphere was investigated as a function of local time, L shell, magnetic latitude, and substorm activity, and the results of this analysis are presented. Specific features of postmidnight chorus are discussed in the context of possible wave-particle interactions occurring during magnetospheric substorms.
626 citations
TL;DR: In this article, the wave vector direction, ellipticity and directions of axes of the polarization ellipse, wave refractive index, transfer function of electric antennas, estimators of the planarity of polarization, and electromagnetic planarity.
Abstract: [1] We describe several newly developed methods for propagation analysis of electromagnetic plasma waves. We make use of singular value decomposition (SVD) technique and we determine the wave vector direction, ellipticity and directions of axes of the polarization ellipse, wave refractive index, transfer function of electric antennas, estimators of the planarity of polarization, and electromagnetic planarity. Simulations of Z-mode waves, which simultaneously propagate with different wave vectors, indicate that the SVD methods give reasonable results even if the assumption on the presence of a single plane wave is invalid. Simulations of whistler mode waves show that these methods can be used to recognize cases when the waves simultaneously propagate with wave vectors in two opposite hemispheres. Finally, we show an example of analysis of natural whistler mode and Z-mode emissions measured in the high-altitude auroral region by the MEMO experiment onboard the INTERBALL spacecraft.
545 citations
TL;DR: In this article, a survey of wave data from the CRRES Plasma Wave Experiment for lower band (0.1-0.5f(ce)) and upper band ( 0.5-1.0f(c)) chorus was presented to assess whether these waves could play an important role in the acceleration of a seed population of electrons to relativistic energies during and following geomagnetic storms.
Abstract: Intense interest currently exists in determining the roles played by various wave-particle interactions in the acceleration of electrons to relativistic energies during/following geomagnetic storms. Here we present a survey of wave data from the CRRES Plasma Wave Experiment for lower band (0.1-0.5f(ce)) and upper band (0.5-1.0f(ce)) chorus, f(ce) being the electron gyrofrequency, to assess whether these waves could play an important role in the acceleration of a seed population of electrons to relativistic energies during and following geomagnetic storms. Outside of the plasmapause the chorus emissions are largely substorm-dependent, and all chorus emissions are enhanced when substorm activity is enhanced. The equatorial chorus (/ lambda (m) / 300 nT) with average amplitudes typically >0.5 mV m(-1) predominantly in the region 3 15 degrees) is strongest in the lower band during active conditions, with average amplitudes typically >0.5 mV m(-1) in the region 3 < L < 7 over a range of local times on the dayside, principally in the range 0600-1500 MLT, Consistent with wave generation in the horns of the magnetosphere. An inner population of weak, substorm-independent emissions with average amplitudes generally < 0.2 mV m(-1) are seen in both bands largely inside L = 4 on the nightside during quiet (AE < 100 nT) and moderate (100 nT < AE < 300 nT) conditions. These emissions lie inside the plasmapause and are attributed to signals from lightning and ground-based VLF transmitters. We conclude that the significant increases in chorus amplitudes seen outside of the plasmapause during substorms support the theory of electron acceleration by whistler mode chorus in that region. The results suggest that electron acceleration by whistle mode chorus during/following geomagnetic storms can only be effective when there are periods of prolonged substorm activity following the main phase of the geomagnetic storm.
509 citations