Using the Event Matrix for Chorus from the Lower Frequency Band to Determine Some Characteristics of Their Excitation Mechanism

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Abstract

The work is devoted to studying the quantitative characteristics of the mechanism of excitation of VLF chorus emissions by means the analysis of high-resolution data from the Van Allen Probe spacecraft. A typical example of chorus with spectral forms in the lower frequency band (below half the electron cyclotron frequency) in the region of the local minimum of the magnetic field behind the plasmapause in the middle magnetosphere has been chosen. The results of wave field measurements in a high-resolution data channel are presented in the form of a rectangular event matrix, each row of which corresponds to one cycle of the wave process. In the event matrix, rows are selected that correspond to those implementation fragments that clearly characterize the natural source of short electromagnetic pulses origin. This made it possible to determine the complex eigen-values of the characteristic equation of the source at the linear stage of excitation of the chorus. The values of the roots of the characteristic equation, established by analyzing the observation data of chorus, correspond to implementation of the mechanism for exciting chorus by amplifying noise electromagnetic pulses in enhanced ducts.

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About the authors

P. A. Bespalov

A.V. Gaponov-Grekhov Institute of Applied Physics of the Russian Academy of Sciences; HSE University

Author for correspondence.
Email: pbespalov@mail.ru
Russian Federation, Nizhny Novgorod; Nizhny Novgorod

O. N. Savina

HSE University

Email: onsavina@mail.ru
Russian Federation, Nizhny Novgorod

G. M. Neshchetkin

A.V. Gaponov-Grekhov Institute of Applied Physics of the Russian Academy of Sciences; HSE University

Email: gmheschetkin@edu.hse.ru
Russian Federation, Nizhny Novgorod; Nizhny Novgorod

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Supplementary files

Supplementary Files
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2. Fig. 1. Spectral shapes of a typical chorus burst with low (a) and high (b) temporal resolution. The white line shows the half of the local electron cyclotron frequency.

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3. Fig. 2. Oscillogram of the wave field, where asterisks show the results of consecutive measurements of the BU-component value.

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4. Fig. 3. Asterisks correspond to known measurements of the BU component of the wave magnetic field, peak values are marked with squares (Uk, Uk + 1) and circles (Dk), the black line is the approximation from cosine fragments based on formulas (14) that we finally constructed.

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5. Fig. 4. Reconstructed roots of the characteristic equation describing the linear stage of chorus excitation. The selection of these 12 clusters in the event matrix was based on keeping the values of γ, ω, φ in consecutive four or more rows with a spread of 10%.

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6. Fig. 5. The result of additionally checking the fulfilment of the pattern (2) for one of the found roots of the characteristic equation.

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7. Fig. 6. Roots of the characteristic equation (c), dynamic spectrum of the signal (b), distribution of roots (a, d).

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8. Fig. 7. Dependence of the frequency ωv on the longitudinal component of the wave vector kz for whistling waves with dispersion equation (12). The dashed line corresponds to the equality of the longitudinal phase and group velocities.

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9. Fig. 8. Result of numerical solution of the characteristic equation (13).

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10. Fig. 9. Background plasma concentration along the spacecraft flight path. The chorus burst shown in Fig. 1b was observed in the interval marked by vertical lines.

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