Survey of Poynting flux of whistler mode chorus in the outer zone

Santolı́k, O.; Pickett, J. S.; Gurnett, D. A.; Menietti, J. D.; Tsurutani, B. T.; Verkhoglyadova, O. P.

doi:10.1029/2009ja014925

Cited by 107 publications

(136 citation statements)

References 53 publications

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“…It is unusual to observe discrete chorus in this MLT sector, although observations of some discrete emissions have been also previously reported (Santolik et al (Santolik 2008) are detected in both cases. During the second case (day 160), the wave spectra also exhibited an increase in frequency as the Cluster spacecraft moves inwards from L = 7 to L = 5.5, corresponding to chorus generation at a fraction of the electron cyclotron frequency (Tsurutani and Smith 1974;Meredith et al 2001;Santolik et al 2010b). This observed signature corresponds to properties of whistler-mode chorus and is strongly suggestive that these waves are indeed chorus.…”

Section: Resultsmentioning

confidence: 99%

Relativistic electron acceleration during HILDCAA events: are precursor CIR magnetic storms important?

et al. 2015

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We present a comparative study of high-intensity long-duration continuous AE activity (HILDCAA) events, both isolated and those occurring in the "recovery phase" of geomagnetic storms induced by corotating interaction regions (CIRs). The aim of this study is to determine the difference, if any, in relativistic electron acceleration and magnetospheric energy deposition. All HILDCAA events in solar cycle 23 (from 1995 through 2008) are used in this study. Isolated HILDCAA events are characterized by enhanced fluxes of relativistic electrons compared to the pre-event flux levels. CIR magnetic storms followed by HILDCAA events show almost the same relativistic electron signatures. Cluster 1 spacecraft showed the presence of intense whistler-mode chorus waves in the outer magnetosphere during all HILDCAA intervals (when Cluster data were available). The storm-related HILDCAA events are characterized by slightly lower solar wind input energy and larger magnetospheric/ionospheric dissipation energy compared with the isolated events. A quantitative assessment shows that the mean ring current dissipation is~34 % higher for the storm-related events relative to the isolated events, whereas Joule heating and auroral precipitation display no (statistically) distinguishable differences. On the average, the isolated events are found to be comparatively weaker and shorter than the storm-related events, although the geomagnetic characteristics of both classes of events bear no statistically significant difference. It is concluded that the CIR storms preceding the HILDCAAs have little to do with the acceleration of relativistic electrons. Our hypothesis is that~10-100-keV electrons are sporadically injected into the magnetosphere during HILDCAA events, the anisotropic electrons continuously generate electromagnetic chorus plasma waves, and the chorus then continuously accelerates the high-energy portion of this electron spectrum to MeV energies.

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Section: Resultsmentioning

confidence: 99%

Relativistic electron acceleration during HILDCAA events: are precursor CIR magnetic storms important?

et al. 2015

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“…This paper thus provides a new model for the generation of weak-amplitude falling-tone chorus elements in the inner magnetosphere and emphasizes the significance of reflected chorus waves for the understanding of the inner magnetosphere dynamics (see also Santolík et al, 2010). Our model predicts that rising-tone chorus elements, which are generated at the equator and magnetospherically reflected to smaller L-shells, can turn into falling-tone elements that are then observed at lower latitudes.…”

Section: Discussionmentioning

confidence: 76%

“…• ) and then be damped at higher latitudes (see, e.g., Kennel and Thorne, 1967;Watt et al, 2012Watt et al, , 2013, and it is very likely that falling tones spectrum would be (taking into account wave dispersion and damping) at least 2 orders of magnitude weaker than source chorus, in accordance with Parrot et al (2004), Santolík et al (2010), and Li et al (2013). In this sense, studies including a model of an outer radiation belt are currently conducted by the authors to estimate chorus-wave growth/damping during their propagation, in a realistic model of Earth's inner magnetosphere.…”

Section: Discussionmentioning

confidence: 90%

On the origin of falling-tone chorus elements in Earth's inner magnetosphere

Breuillard¹,

Agapitov

Artemyev

et al. 2014

Ann. Geophys.

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Abstract. Generation of extremely/very low frequency (ELF/VLF) chorus waves in Earth's inner magnetosphere has received increased attention recently because of their significance for radiation belt dynamics. Though past theoretical and numerical models have demonstrated how risingtone chorus elements are produced, falling-tone chorus element generation has yet to be explained. Our new model proposes that weak-amplitude falling-tone chorus elements can be generated by magnetospheric reflection of rising-tone elements. Using ray tracing in a realistic plasma model of the inner magnetosphere, we demonstrate that rising-tone elements originating at the magnetic equator propagate to higher latitudes. Upon reflection there, they propagate to lower Lshells and turn into oblique falling tones of reduced power, frequency, and bandwidth relative to their progenitor rising tones. Our results are in good agreement with comprehensive statistical studies of such waves, notably using magnetic field measurements from THEMIS (Time History of Events and Macroscale Interactions during Substorms) spacecraft. Thus, we conclude that the proposed mechanism can be responsible for the generation of weak-amplitude falling-tone chorus emissions.

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“…Â P can reach 60 ı in the high-frequency band. Santolik et al [2010] show that the low-frequency chorus band has median values of Â P = 10 [32] We show that the thermal corrections can explain a transition to elliptical polarization of chorus waves. Santolik et al [2010, see Figure 3] statistical results for the highfrequency band chorus ellipticity show a transition from right-hand circularly polarized modes to elliptical < 1, linear and right-hand circular polarized as ELF wave frequencies approach !…”

Section: Discussionmentioning

confidence: 99%

“…Recently, several studies analyzed the Poynting flux for chorus in the outer magnetosphere and hiss inside the plasmasphere [LeDocq et al, 1998;Santolik et al, 2010;Haque et al, 2010;Tsurutani et al, 2011Tsurutani et al, , 2012Agapitov et al, 2011Agapitov et al, , 2012. The standard definition of the Poynting flux vector (in the Gaussian system of units) is [Stix, 1992]:…”

Section: Introductionmentioning

confidence: 99%

Theoretical analysis of Poynting flux and polarization for ELF‐VLF electromagnetic waves in the Earth's magnetosphere

Verkhoglyadova

Tsurutani

Lakhina³

2013

JGR Space Physics

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[1] We discuss properties of extremely low-frequency (ELF) and very low-frequency (VLF) electromagnetic waves in the Earth's magnetosphere. General expressions for wave magnetic field polarization and for the angle Â P between the direction of the Poynting flux vector and the ambient magnetic field are derived for low-amplitude (linear) waves taking into account first-order finite gyroradius effects. The wave magnetic field is always in a plane perpendicular to the direction of the wave propagation, and the polarization depends on wave frequency (or wavelength), dispersion, and plasma parameters. In a warm plasma, the Poynting flux is not aligned with the group velocity and generally deviates from the wave propagation direction, except for parallel propagation. Numerical estimates for Â P and wave polarization are made for plasmaspheric hiss (at L = 2, 4, and 6) for typical plasma parameters and for the case of elevated electron temperature (5 keV). The plasmaspheric hiss wave magnetic field is right-hand circularly polarized, except for highly oblique hiss waves which are elliptically polarized. We note a possible transition to the magnetosonic wave regime at short wavelengths. The maximum Poynting flux angle is 20 ı . Estimates for daytime outer zone chorus (L = 6) show two regions of oblique Poynting flux corresponding to a low-frequency band (! < ! ce /2) and to a high-frequency band (! ce /2 < ! < ! ce ) where ! and ! ce are the wave frequency and the electron cyclotron frequency, respectively. The wave magnetic field polarization varies from circular to elliptical at shorter wavelengths. In a hot plasma, chorus is elliptically polarized. The maximum Â P in the low-frequency band is 20 ı . Â P can reach 60 ı in the high-frequency band. Our results are consistent with the Poynting flux statistics of Polar measurements.Citation: Verkhoglyadova, O. P., B. T. Tsurutani, and G. S. Lakhina (2013), Theoretical analysis of Poynting flux and polarization for ELF-VLF electromagnetic waves in the Earth's magnetosphere,

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Survey of Poynting flux of whistler mode chorus in the outer zone

Cited by 107 publications

References 53 publications

Relativistic electron acceleration during HILDCAA events: are precursor CIR magnetic storms important?

Relativistic electron acceleration during HILDCAA events: are precursor CIR magnetic storms important?

On the origin of falling-tone chorus elements in Earth's inner magnetosphere

Theoretical analysis of Poynting flux and polarization for ELF‐VLF electromagnetic waves in the Earth's magnetosphere

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