Generation mechanism of Z-mode waves in the equatorial plasmasphere

Nishimura, Y.; Ono, Takayuki; Iizima, M.; Shinbori, Atsuki; Kumamoto, A.

doi:10.1186/bf03352043

Cited by 4 publications

(2 citation statements)

References 26 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The complex frequency is defined as ω ≡ ω r + iω i , where ω r is the real part of ω and the imaginary part ω i is the wave growth rate. With reference to Lee et al [1979] and Nishimura et al [2007], the linearized growth rate ω i , is written as where ω p is the local plasma frequency, n s is the electron density of the s th species ( s , hot and cold plasma), and J n = J n ( b ) is the n th‐order Bessel function depending on b ≡ k ⊥ u ⊥ / ω c . It should be noted that is derived under the assumptions ω i ≪ ω r and k ⊥ u ⊥ / ω c ≪ 1.…”

Section: Mathematical Description Of Direct Generationmentioning

confidence: 99%

Direct and indirect generation of Jovian quasiperiodic radio bursts by relativistic electron beams in the polar magnetosphere

et al. 2011

View full text Add to dashboard Cite

[1] The Jovian polar magnetosphere has relativistic particle accelerations with quasiperiodicity (QP accelerations), which are accompanied by periodic auroral emissions and low-frequency radio bursts called QP bursts. Although there have been some observations, the generation process of QP bursts by relativistic electrons from QP accelerations has not been revealed yet. This paper presents calculated wave growth rates for the discussion of the QP radio burst generation processes based on wave generation theories. Linear growth rates were computed for free space mode waves and plasma waves in cold plasma dispersion relations, assuming that these waves are generated by relativistic electron beams in two kinds of polar source regions, as suggested by wave observations and by the ray-tracing results reported in our previous studies. One of the source regions is at high altitudes where emission frequency f is close to local right-handed extraordinary (RX) mode cutoff frequency f RX and the other is at low altitudes where f is close to local plasma frequency f p . We found that ordinary (O) mode free space waves are sufficiently amplified, with broad beaming at both of the sources in the duration of the relativistic electron populations when they have an unstable velocity distribution like a ring beam structure. This means that O mode free space waves can be generated directly from energetic electrons via the "cyclotron maser instability" (CMI) process. We also confirmed that extraordinary (X) mode free space waves are not sufficiently amplified at both of the sources in the beam duration but Z mode waves propagating along field lines from the sources toward the Jovian polar ionosphere are significantly excited. Z mode waves propagating toward the planet could be converted to free space O mode waves at a steep plasma density gradient via the "mode conversion" (MC) process. We conclude that both direct (CMI) and indirect (MC) process can generate O mode QP radio bursts with radiation characteristics consistent with those observed by spacecraft. This suggests that relativistic electrons with unstable velocity distributions are generated by the QP acceleration and that Z mode and O mode QP radio bursts are excited by these particles.Citation: Kimura, T., F. Tsuchiya, H. Misawa, A. Morioka, and Y. Nishimura (2011), Direct and indirect generation of Jovian quasiperiodic radio bursts by relativistic electron beams in the polar magnetosphere,

show abstract

Section: Mathematical Description Of Direct Generationmentioning

confidence: 99%

Direct and indirect generation of Jovian quasiperiodic radio bursts by relativistic electron beams in the polar magnetosphere

et al. 2011

View full text Add to dashboard Cite

show abstract

“…However, they have not performed detailed evaluation (e.g., wave frequency dependence, wave intensity dependence, regional dependence, and geomagnetic condition dependence). For example, UHR emission intensity exhibits temporal variation (Nishimura et al, 2007), and there are several mechanisms for sudden intense of UHR emission (e.g., equatorial enhancement of the plasma wave turbulence [EPWAT, Oya et al, 1991] and enhancement of UHR intensities associated with substorms, Morioka & Oya, 1996). In order to put this automatic technique into practical purpose, we need to confirm that the automatic determined UHR frequencies have enough quality to investigate the density variations in the inner magnetosphere.…”

Section: Introductionmentioning

confidence: 99%

Detection of UHR Frequencies by a Convolutional Neural Network From Arase/PWE Data

et al. 2020

Self Cite

View full text Add to dashboard Cite

We have developed the automatic detection scheme for upper hybrid resonance (UHR) frequency using a convolutional neural network (CNN) from the electric field spectra obtained by the plasma wave experiment (PWE) aboard Arase. In this paper, we investigate the practical capability of this scheme in terms of actual scientific use case. We find that the average error rate is below 7.8% when the wave frequency is above 30 kHz and the wave spectral intensity is less than 10 −5 mV 2/m 2 /Hz. About 91% of the data obtained by the high-frequency analyzer (HFA) aboard the Arase satellite satisfies these conditions. To improve the accuracy of the determined UHR frequencies in a wide frequency range, we used another receiver, the onboard frequency analyzer (OFA), which enables us to detect low-frequency UHR emissions. We confirmed that the averaged error rate derived by the OFA spectra becomes better than that derived from the HFA spectra in a frequency range below 20 kHz. We report the performance of the UHR frequency determination under the different geomagnetic conditions. We find that the UHR frequency can be determined with good accuracy using the CNN from the frequency-time diagram both during geomagnetically quiet and disturbed conditions. We conclude that the CNN-based UHR frequency determination is a reliable method to derive the electron density along the satellite orbit through observations of UHR frequencies, and this method contributes to studies on dynamics of the plasmasphere. Plain Language Summary Determining the upper hybrid resonance (UHR) frequency is the most popular way to determine the quantitative electron density in space. The high-frequency analyzer (HFA) and onboard frequency analyzer (OFA) aboard the Arase satellite measure electric field spectra at high-and low-frequency ranges. The nominal time resolutions of the HFA and OFA spectra are 8 and 1 s, respectively. Determining the UHR frequency by conventional visual inspection requires huge resources for researchers; therefore, some automatic determination methods have been proposed in recent years. In this study, we evaluate the accuracy of UHR frequency determination by convolutional neural networks (CNN). We find that the averaged error rate of the automatically determined UHR frequency is less than 7.8% for the most events (91% of the data set), and we conclude that the CNN-based UHR frequency determination is the reliable method to estimate the electron density along the satellite orbit.

show abstract

A Simulation Study of the Plasma Wave Enhancements in the Earth’s Equatorial Plasmasphere

2013

View full text Add to dashboard Cite

Generation mechanism of Z-mode waves in the equatorial plasmasphere

Cited by 4 publications

References 26 publications

Direct and indirect generation of Jovian quasiperiodic radio bursts by relativistic electron beams in the polar magnetosphere

Direct and indirect generation of Jovian quasiperiodic radio bursts by relativistic electron beams in the polar magnetosphere

Detection of UHR Frequencies by a Convolutional Neural Network From Arase/PWE Data

A Simulation Study of the Plasma Wave Enhancements in the Earth’s Equatorial Plasmasphere

Contact Info

Product

Resources

About