Correlation scales of chorus emissions observed by THEMIS Vitalii - - PowerPoint PPT Presentation

Introduction Data selection Bw distribution Chorus spatial correlation scales Chorus temporal correlation scales Conclusions

Correlation scales of chorus emissions observed by THEMIS

Vitalii Shastun1, Vladimir Krasnoselskikh1, Oleksiy Agapitov2

1Laboratoire de Physique et Chimie de l’Environnement et de l’Espace 2Space Science Laboratory, the University of California

vitalii.shastun@cnrs-orleans.fr

November 16th 2016

Vitalii Shastun, Vladimir Krasnoselskikh, Oleksiy Agapitov LPC2E, CNRS ELF/VLF correlation properties

Introduction Data selection Bw distribution Chorus spatial correlation scales Chorus temporal correlation scales Conclusions

Radiation Belts

Figure: Two radiation belts around Earth. Image Credit: NASA Figure: Positions of geostationary, GPS, GLONASS, Galileo, and orbits, with the Van Allen radiation belts and the Earth to scale

Vitalii Shastun, Vladimir Krasnoselskikh, Oleksiy Agapitov LPC2E, CNRS ELF/VLF correlation properties

Introduction Data selection Bw distribution Chorus spatial correlation scales Chorus temporal correlation scales Conclusions

Dynamics of Radiation Belts

Favoured mechanisms for driving in-situ acceleration/scattering of charged particles in radiation belts: Chorus/hiss waves EMIC waves Magnetosonic waves Nonlinear time-domain structures

Figure: Energy flow in plasma turbulence

Vitalii Shastun, Vladimir Krasnoselskikh, Oleksiy Agapitov LPC2E, CNRS ELF/VLF correlation properties

Introduction Data selection Bw distribution Chorus spatial correlation scales Chorus temporal correlation scales Conclusions

Chorus Active Region Structure

Figure: Schematic illustration of Bw magnetic field perturbation structure in a vicinity of the chorus wave source.

Vitalii Shastun, Vladimir Krasnoselskikh, Oleksiy Agapitov LPC2E, CNRS ELF/VLF correlation properties

Introduction Data selection Bw distribution Chorus spatial correlation scales Chorus temporal correlation scales Conclusions

Themis Mission

Figure: The individual orbits of THEMIS spacecraft

Orbit parameters: Perigee: 470 km Apogee: 87330 km Inclination: 16◦ Period: 1870 min

Vitalii Shastun, Vladimir Krasnoselskikh, Oleksiy Agapitov LPC2E, CNRS ELF/VLF correlation properties

Introduction Data selection Bw distribution Chorus spatial correlation scales Chorus temporal correlation scales Conclusions

Data Selection

Data source Frequency range Sampling rate Data used SCM waveforms 0.1 - 8000 Hz 8192 S/s 2007 - 2008 Filter bank (FBK) 80 - 6000 Hz 4 S/s 2008 - 2015

Table: Instrument summary

Vitalii Shastun, Vladimir Krasnoselskikh, Oleksiy Agapitov LPC2E, CNRS ELF/VLF correlation properties

Introduction Data selection Bw distribution Chorus spatial correlation scales Chorus temporal correlation scales Conclusions

Magnetic Field Spectrograms

Figure: Time-frequency power spectrograms of the wave magnetic field (a) calculated from waveformes and (b) obtained from FBK (17th July 2007).

Vitalii Shastun, Vladimir Krasnoselskikh, Oleksiy Agapitov LPC2E, CNRS ELF/VLF correlation properties

Introduction Data selection Bw distribution Chorus spatial correlation scales Chorus temporal correlation scales Conclusions

Bw distributions

Figure: Occurrence rate of chorus emissions and RMS values of magnetic component of chorus waves for different levels of geomagnetic activities.

Vitalii Shastun, Vladimir Krasnoselskikh, Oleksiy Agapitov LPC2E, CNRS ELF/VLF correlation properties

Introduction Data selection Bw distribution Chorus spatial correlation scales Chorus temporal correlation scales Conclusions

Spatial Correlation Scales

Figure: Cumulative PDF of cross-correlation values of whistler wave measurements.

ρBa

w,Bb w = ρ(Ba

w(t), Bb w(t+dt))

a, b ∈ {THA, THD, THE}

Figure: Computation scheme

Vitalii Shastun, Vladimir Krasnoselskikh, Oleksiy Agapitov LPC2E, CNRS ELF/VLF correlation properties

Introduction Data selection Bw distribution Chorus spatial correlation scales Chorus temporal correlation scales Conclusions

Correlation Time Distribution

Figure: Occurence rate of whistler waves with cross-correlation value between two adjacent THEMIS s/c greater than 0.5 in L-shell/MLT (left)

• domain. Panels a), b), and c) correspond to frequency ranges 80-227 Hz,

316-904 Hz, and 1390-5994 Hz.

Vitalii Shastun, Vladimir Krasnoselskikh, Oleksiy Agapitov LPC2E, CNRS ELF/VLF correlation properties

Introduction Data selection Bw distribution Chorus spatial correlation scales Chorus temporal correlation scales Conclusions

Correlation Time Computation Scheme

f (x) = c1Gs(0, σ1) + c2Gs(µ2, σ2) Gs - Gaussian function µ2 - position of the centre of gaussian function σ1, σ2 - width of the “bell” σ1 - characteristic correlation time of low-intensity noise µ2 - characteristic correlation time of high-intensity chorus emissions

Vitalii Shastun, Vladimir Krasnoselskikh, Oleksiy Agapitov LPC2E, CNRS ELF/VLF correlation properties

Introduction Data selection Bw distribution Chorus spatial correlation scales Chorus temporal correlation scales Conclusions

Correlation Time Distribution

Figure: Whistler wave correlation time distribution at four different regions of the equatorial magnetosphere registered by THA during 2008-2014.

Vitalii Shastun, Vladimir Krasnoselskikh, Oleksiy Agapitov LPC2E, CNRS ELF/VLF correlation properties

Introduction Data selection Bw distribution Chorus spatial correlation scales Chorus temporal correlation scales Conclusions

Figure: (a) Distribution of chorus wave correlation times at different radial distances of equatorial magnetosphere registered by THA during 2008-2014. (b) Chorus emission characteristic correlation time dependency on L-shell.

Vitalii Shastun, Vladimir Krasnoselskikh, Oleksiy Agapitov LPC2E, CNRS ELF/VLF correlation properties

Introduction Data selection Bw distribution Chorus spatial correlation scales Chorus temporal correlation scales Conclusions

Conclusions

The distributions of chorus wave occurrence rate and amplitude, as well as spatial correlation scales and temporal extents of active chorus regions were examined statistically using multi-spacecraft measurements of the THEMIS project during 2008-2014. Based on THEMIS FBK waves spectral power data collected during 2008-2014, the correlation scales of chorus wave packets in the

• uter radiation belt (4 < L < 9) has been found to be ∼ 500 km.

The statistics of temporal correlation of chorus wave amplitudes distinguished two regimes depending upon the wave amplitude (actually presence of chorus waves), when tcorr is about 200-300 s (with strong dependence on L-shell) provided the characteristic time scale for the chorus region; and noise-like signal with tcorr ≤ 50 s.

Vitalii Shastun, Vladimir Krasnoselskikh, Oleksiy Agapitov LPC2E, CNRS ELF/VLF correlation properties