A Model of the Subpacket Structure of Rising Tone Chorus Emissions

Hanzelka, Miroslav; Santolı́k, O.; Omura, Yoshiharu; Kolmašová, Ivana; Kletzing, C.

doi:10.1002/essoar.10503189.1

Cited by 12 publications

(20 citation statements)

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“…In previous simulations and observations (Hanzelka et al., 2020; Katoh & Omura, 2013; Lu et al., 2019; Nunn, 1986; Omura et al., 2008; Santolík, Gurnett, Pickett, Parrot, & Cornilleau‐Wehrlin, 2004; Tao, 2014), a chorus element usually exhibits a two‐level structure “element‐subpackets.” The discrete elements can be identified in the frequency‐time spectra and the subpackets manifest as amplitude modulation in waveform (e.g., Figure 2 in Tsurutani et al., 2020 and Figure 3 in Tao, 2014). The subpacket is considered as the basic unit of an element to form the frequency sweep (Omura & Nunn, 2011) or is formed due to the oscillation of phase‐trapped electron momentum (Tao et al., 2017).…”

Section: Discussionmentioning

confidence: 93%

Observation of Unusual Chorus Elements by Van Allen Probes

et al. 2021

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Section: Discussionmentioning

confidence: 93%

Observation of Unusual Chorus Elements by Van Allen Probes

et al. 2021

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“…Nunn et al (2005) have provided an explanation for rising tones with upper sideband instability allowiing successive jumps to the next upper sideband through the establishment of a spatial frequency gradient by the out‐of‐phase portion of the resonant current. Hanzelka et al (2020) have derived a new model for the formation of subelements. The latter authors assume that the resonant current is released and propagates upstream to generate a new whistler wave with increased frequency.…”

Section: Discussionmentioning

confidence: 99%

Lower‐Band “Monochromatic” Chorus Riser Subelement/Wave Packet Observations

et al. 2020

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Three lower-band (f < 0.5 fce) chorus riser elements detected in the dayside generation region were studied in detail using the Van Allen Probe data. Two subelements/wave packets within each riser were examined for their wave "frequency" constancy within seven consecutive wave cycles. The seven wave cycles contained the maximum amplitudes of the subelements/packets. Maximum variance B1 zero crossings were used for the identification of wave cycle start and stop times. It is found that the frequency is constant to within~3% (one standard deviation), with no evidence of upward frequency sweeping over the seven cycles. Continuous wavelet power spectra for the duration of the seven cycles confirm this conclusion. The implication is that a chorus riser element is composed of coherent approximately "monochromatic" steps instead of a gradual sweep in frequency over the whole element. There was no upward frequency stepping where the wave amplitude was the largest, contrary to the sideband theory prediction. It is shown that a chorus riser involves instability of cyclotron resonant energetic electrons from~6 to~40 keV at L = 5.8, that is, essentially the whole substorm electron energy spectrum. The above findings may have important consequences for possible wave generation mechanisms. Some new ideas for mechanisms are suggested in conclusion.

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“…Besides, both results of Hanzelka et al. (2020) and Shoji and Omura (2013) are based on the sequential triggering model; therefore, comments above about the differences between the two models regarding how chirping and subpackets occur still apply.…”

Section: Comparison With Previous Modelsmentioning

confidence: 99%

“…Each frequency sweeping from

ω

ω + δ ω

forms a subpacket. In this sense, chorus subpacket can be considered as the basic unit of wave excitation (Hanzelka et al., 2020; Katoh & Omura, 2013; Shoji & Omura, 2013). However, in the TaRA model, subpackets are formed by the conservation of momentum and energy between waves and phase‐trapped electrons, see Section 7 or Tao et al.…”

Section: Comparison With Previous Modelsmentioning

confidence: 99%

“…Following Shoji and Omura (2013), Hanzelka et al. (2020) developed a model of subpackets based on the sequential triggering model, which also has the feature of wave generation in the upstream. Unlike the TaRA model, however, the generated new emission is not due to the selective amplification through phase‐locking at the release point, but due to

δ j_{B}

formed by nonlinear interactions with the previous triggering wave at the previous triggering point.…”

Section: Comparison With Previous Modelsmentioning

confidence: 99%

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A “Trap‐Release‐Amplify” Model of Chorus Waves

2021

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Whistler mode chorus waves are quasi‐coherent electromagnetic emissions with frequency chirping. Various models have been proposed to understand the chirping mechanism, which is a long‐standing problem in space plasmas. Based on analysis of effective wave growth rate and electron phase space dynamics in a self‐consistent particle simulation, we propose a phenomenological model called the “Trap‐Release‐Amplify” (TaRA) model for chorus. In this model, phase space structures of correlated electrons are formed by nonlinear wave particle interactions, which mainly occur in the downstream of equator. When released from the wave packet in the upstream, these electrons lead to selective amplification of new emissions which satisfy the phase‐locking condition to maximize wave power transfer, resulting in frequency chirping. The phase‐locking condition at the release point gives a chirping rate that is, fully consistent with the one by Helliwell in case of a nonuniform background magnetic field. The nonlinear wave particle interaction part of the TaRA model results in a chirping rate that is, proportional to wave amplitude, a conclusion originally reached by Vomvoridis et al. Therefore, the TaRA model unifies two different results from seemingly unrelated studies. Furthermore, the TaRA model naturally explains fine structures of chorus waves, including subpackets and bandwidth, and their evolution through dynamics of phase‐trapped electrons. Finally, we suggest that this model could be applied to explain other related phenomena, including frequency chirping of chorus in a uniform background magnetic field and of electromagnetic ion cyclotron waves in the magnetosphere.

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A Model of the Subpacket Structure of Rising Tone Chorus Emissions

Cited by 12 publications

References 0 publications

Observation of Unusual Chorus Elements by Van Allen Probes

Observation of Unusual Chorus Elements by Van Allen Probes

Lower‐Band “Monochromatic” Chorus Riser Subelement/Wave Packet Observations

A “Trap‐Release‐Amplify” Model of Chorus Waves

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