Introduction Data selection B w distribution Chorus spatial correlation scales Chorus temporal correlation scales Conclusions Correlation scales of chorus emissions observed by THEMIS Vitalii Shastun 1 , Vladimir Krasnoselskikh 1 , Oleksiy Agapitov 2 1 Laboratoire de Physique et Chimie de l’Environnement et de l’Espace 2 Space 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 B w distribution Chorus spatial correlation scales Chorus temporal correlation scales Conclusions Radiation Belts Figure: Positions of Figure: Two radiation belts geostationary, GPS, GLONASS, around Earth. Image Credit: Galileo, and orbits, with the Van NASA Allen radiation belts and the Earth to scale Vitalii Shastun, Vladimir Krasnoselskikh, Oleksiy Agapitov LPC2E, CNRS ELF/VLF correlation properties
Introduction Data selection B w 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 Figure: Energy flow in plasma structures turbulence Vitalii Shastun, Vladimir Krasnoselskikh, Oleksiy Agapitov LPC2E, CNRS ELF/VLF correlation properties
Introduction Data selection B w distribution Chorus spatial correlation scales Chorus temporal correlation scales Conclusions Chorus Active Region Structure Figure: Schematic illustration of B w 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 B w distribution Chorus spatial correlation scales Chorus temporal correlation scales Conclusions Themis Mission Orbit parameters: Perigee: 470 km Apogee: 87330 km Inclination: 16 ◦ Period: 1870 min Figure: The individual orbits of THEMIS spacecraft Vitalii Shastun, Vladimir Krasnoselskikh, Oleksiy Agapitov LPC2E, CNRS ELF/VLF correlation properties
Introduction Data selection B w 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 B w 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 B w distribution Chorus spatial correlation scales Chorus temporal correlation scales Conclusions B w 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 B w distribution Chorus spatial correlation scales Chorus temporal correlation scales Conclusions Spatial Correlation Scales w = ρ ( B a w ( t ) , B b w ( t + dt )) ρ B a w , B b a , b ∈ { THA , THD , THE } Figure: Computation scheme Figure: Cumulative PDF of cross-correlation values of whistler wave measurements. Vitalii Shastun, Vladimir Krasnoselskikh, Oleksiy Agapitov LPC2E, CNRS ELF/VLF correlation properties
Introduction Data selection B w 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 B w distribution Chorus spatial correlation scales Chorus temporal correlation scales Conclusions Correlation Time Computation Scheme f ( x ) = c 1 G s (0 , σ 1 ) + c 2 G s ( µ 2 , σ 2 ) G s - Gaussian function µ 2 - position of the centre of gaussian function σ 1 , σ 2 - width of the “bell” σ 1 - characteristic correlation time of low-intensity noise µ 2 - characteristic correlation time of high-intensity chorus emissions Vitalii Shastun, Vladimir Krasnoselskikh, Oleksiy Agapitov LPC2E, CNRS ELF/VLF correlation properties
Introduction Data selection B w 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 B w 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 B w 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 outer 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 t corr 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 t corr ≤ 50 s. Vitalii Shastun, Vladimir Krasnoselskikh, Oleksiy Agapitov LPC2E, CNRS ELF/VLF correlation properties
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