HAL (Le Centre pour la Communication Scientifique Directe), Oct 7, 2019
International audienceNatural emissions of whistler-mode electromagnetic waves, especially chorus... more International audienceNatural emissions of whistler-mode electromagnetic waves, especially chorus and hiss, can influence the dynamics of the Van Allen radiation belts via quasi-linear or nonlinear wave particle interactions. They can play a role in complex processes of the energy transfer between different electron populations. To separate temporal and spatial variations of their characteristics, measurements at different points in space are necessary. We show initial results of measurements of the Cluster space fleet during the period of close separations between Cluster 3 and Cluster 4 from September to December 2018. As the separations of these spacecraft decrease down to 3 km in the equatorial source region of chorus we can perform systematic phase measurements of nonlinear wave packets of chorus. The embedded fine structure of sub-packets is particularly interesting in this context because their spatio-temporal scales have been shown to be much shorter compared to scales of the chorus wave packets. We use detailed waveform measurements of the WBD instruments onboard Cluster 3 and Cluster 4 close to the equator, with Cluster 1 and/or Cluster 2 located at much larger separations at higher latitudes. These detailed measurements are put in the context of overall wave propagation and polarization patterns by multi-component data of the STAFF-SA instruments onboard all the 4 Cluster spacecraft, with the FGM instruments used to define the magnetic field-aligned coordinate system and to normalize the measured frequencies by the electron cyclotron frequency
Identification of natural plasma emissions observed close to the plasmapause by the Cluster-Whisp... more Identification of natural plasma emissions observed close to the plasmapause by the Cluster-Whisper relaxation sounder
The Whisper instruments on Cluster frequently observe the electromagnetic contin- uum radiation i... more The Whisper instruments on Cluster frequently observe the electromagnetic contin- uum radiation in the frequency range 2-80 kHz. The high sensitivity and time resolu- tion of Whisper allow observations of the fine structures and polarization of the emis- sions, which are detected up to the plasmapause that is a known source region. We use here the polarization and directivity information combined from the four Whisper instruments, as well as the clear relationship between the electrostatic waves seen at the plasmapause and the escaping electromagnetic radiation to provide further indica- tions on its generation mechanism. The diagnostic capabilities offered by the active resonances triggered by the Whisper relaxation sounder strongly suggest that a sig- nificant part of the emissions is coming from electrostatic emissions generated at the zero group velocity of the Bernstein modes (Fq frequency)
ABSTRACT Gyroresonant wave particle interactions with whistler mode chorus play a fundamental rol... more ABSTRACT Gyroresonant wave particle interactions with whistler mode chorus play a fundamental role in the dynamics of the Earth's radiation belts and inner magnetosphere, affecting both the acceleration and loss of radiation belt electrons. Knowledge of the variability of chorus wave power as a function of both spatial location and geomagnetic activity, required for the computation of pitch angle and energy diffusion rates, is thus a critical input for global radiation belt models. Here we present a global model of lower band (0.1fce < f < 0.5fce) and upper band (0.5fce < f < fce) chorus, where fce is the local electron gyrofrequency, using plasma wave data from DE1, CRRES, Cluster 1, Double Star TC1 and THEMIS, extending the coverage and improving the statistics of existing models. The chorus emissions extend from the plasmapause out to L* = 10 and are found to be largely substorm dependent with the largest intensities being seen during active conditions. Equatorial lower band chorus is strongest during active conditions with peak intensities of the order 2000 pT2 in the region 4 < L* < 9 between 2300 and 1200 MLT. Equatorial upper band chorus is both weaker and less extensive with peak intensities of the order a few hundred pT2 during active conditions between 2300 and 1100 MLT from L* = 3 to L* = 7. Moving away from the equator mid-latitude chorus is strongest in the lower band during active conditions with peak intensities of the order 2000 pT2 in the region 4 < L* < 9 but is restricted to the dayside between 0700 and 1400 MLT. The results suggest that including wave particle interactions beyond geostationary orbit could be very important for global radiation belt models.
International audienceThe main target of the Cluster inner magnetosphere campaign (July-October 2... more International audienceThe main target of the Cluster inner magnetosphere campaign (July-October 2013) is to identify linear and nonlinear processes that affect EMIC, equatorial magnetosonic and chorus waves. The present study examines equatorial magnetosonic waves that are regularly observed under the arch of the plasmasphere, due to the formation of a natural waveguide like structure. These waves are usually observed in the frequency range from a few tens to hundreds of Hz. The spectrum exhibits a banded structure whose spacing is of the order of the ion gyrofrequency in the source region. This fine structure results in complications for the identification of the wave dispersion using data from multispacecraft separated by distances of around 10-100 km. It is shown how this complication can be resolved. The resulting dispersion of the observed waves is presented and compared with analytical solutions
Intense kHz waves generated by electron cyclotron resonance are often observed by the STAFF instr... more Intense kHz waves generated by electron cyclotron resonance are often observed by the STAFF instrument on the TC-1 Double Star spacecraft These electromagnetic waves with frequencies below fce are thought to be associated with the diffuse aurora together with higher frequency electrostatic electron cyclotron harmonic waves As part of the DWP instrumentation on board the Double Star Equator TC-1 spacecraft
Plasma emissions, electromagnetic or electrostatic, are very good tracers of the phenomena occuri... more Plasma emissions, electromagnetic or electrostatic, are very good tracers of the phenomena occuring in space plasma. The Whisper instruments on board each of the Cluster spacecraft regularly monitor the plasma waves related to the plasma dynamics in the various regions of the magnetosphere such as the cusp, entry layer, magnetosheath, magnetopause, plasmasheet and its boundary layer, or plasmapause. Although most of these signatures have already been observed by past missions, the good sensitivity, time and frequency resolution of Whisper, combined with the vantage of the four viewpoints, allow new insight into the plasma mechanisms at their origin, locally or remotely. The most significant observations collected so far by Whisper, with supporting data from other wave instruments, both at close (100 km) and large (above 2000 km) spacecraft separations will be presented and discussed.
Journal of Geophysical Research: Space Physics, 2010
Broadband electrons (BBEs) exhibit remarkable electron flux enhancements over a broad energy rang... more Broadband electrons (BBEs) exhibit remarkable electron flux enhancements over a broad energy range (0.03–30 keV) near the equatorward edge of the auroral oval during geomagnetic storms. Here, we report a BBE event observed by the Fast Auroral Snapshot (FAST) satellite at 1355–1359 UT, ∼61°–66° invariant latitudes, ∼0600 magnetic local time (MLT), and ∼3800 km altitude during a storm on 25 July 2004. The Double Star (DS) TC1 satellite was located near the magnetic equator at L = 5.7, close to the same local time as FAST. We investigate the acceleration process of BBEs from the inner magnetosphere to near the ionosphere by comparing electron data obtained by FAST and DS TC1. We also investigate both plasma and field variations in the inner magnetosphere associated with substorm onset using DS TC1 data to examine the relationship between the BBEs and the storm time substorm. Ground geomagnetic field data show a positive H‐bay at ∼1349 UT at ∼0600 MLT, indicating that a storm time subst...
HAL (Le Centre pour la Communication Scientifique Directe), Oct 7, 2019
International audienceNatural emissions of whistler-mode electromagnetic waves, especially chorus... more International audienceNatural emissions of whistler-mode electromagnetic waves, especially chorus and hiss, can influence the dynamics of the Van Allen radiation belts via quasi-linear or nonlinear wave particle interactions. They can play a role in complex processes of the energy transfer between different electron populations. To separate temporal and spatial variations of their characteristics, measurements at different points in space are necessary. We show initial results of measurements of the Cluster space fleet during the period of close separations between Cluster 3 and Cluster 4 from September to December 2018. As the separations of these spacecraft decrease down to 3 km in the equatorial source region of chorus we can perform systematic phase measurements of nonlinear wave packets of chorus. The embedded fine structure of sub-packets is particularly interesting in this context because their spatio-temporal scales have been shown to be much shorter compared to scales of the chorus wave packets. We use detailed waveform measurements of the WBD instruments onboard Cluster 3 and Cluster 4 close to the equator, with Cluster 1 and/or Cluster 2 located at much larger separations at higher latitudes. These detailed measurements are put in the context of overall wave propagation and polarization patterns by multi-component data of the STAFF-SA instruments onboard all the 4 Cluster spacecraft, with the FGM instruments used to define the magnetic field-aligned coordinate system and to normalize the measured frequencies by the electron cyclotron frequency
Identification of natural plasma emissions observed close to the plasmapause by the Cluster-Whisp... more Identification of natural plasma emissions observed close to the plasmapause by the Cluster-Whisper relaxation sounder
The Whisper instruments on Cluster frequently observe the electromagnetic contin- uum radiation i... more The Whisper instruments on Cluster frequently observe the electromagnetic contin- uum radiation in the frequency range 2-80 kHz. The high sensitivity and time resolu- tion of Whisper allow observations of the fine structures and polarization of the emis- sions, which are detected up to the plasmapause that is a known source region. We use here the polarization and directivity information combined from the four Whisper instruments, as well as the clear relationship between the electrostatic waves seen at the plasmapause and the escaping electromagnetic radiation to provide further indica- tions on its generation mechanism. The diagnostic capabilities offered by the active resonances triggered by the Whisper relaxation sounder strongly suggest that a sig- nificant part of the emissions is coming from electrostatic emissions generated at the zero group velocity of the Bernstein modes (Fq frequency)
ABSTRACT Gyroresonant wave particle interactions with whistler mode chorus play a fundamental rol... more ABSTRACT Gyroresonant wave particle interactions with whistler mode chorus play a fundamental role in the dynamics of the Earth's radiation belts and inner magnetosphere, affecting both the acceleration and loss of radiation belt electrons. Knowledge of the variability of chorus wave power as a function of both spatial location and geomagnetic activity, required for the computation of pitch angle and energy diffusion rates, is thus a critical input for global radiation belt models. Here we present a global model of lower band (0.1fce < f < 0.5fce) and upper band (0.5fce < f < fce) chorus, where fce is the local electron gyrofrequency, using plasma wave data from DE1, CRRES, Cluster 1, Double Star TC1 and THEMIS, extending the coverage and improving the statistics of existing models. The chorus emissions extend from the plasmapause out to L* = 10 and are found to be largely substorm dependent with the largest intensities being seen during active conditions. Equatorial lower band chorus is strongest during active conditions with peak intensities of the order 2000 pT2 in the region 4 < L* < 9 between 2300 and 1200 MLT. Equatorial upper band chorus is both weaker and less extensive with peak intensities of the order a few hundred pT2 during active conditions between 2300 and 1100 MLT from L* = 3 to L* = 7. Moving away from the equator mid-latitude chorus is strongest in the lower band during active conditions with peak intensities of the order 2000 pT2 in the region 4 < L* < 9 but is restricted to the dayside between 0700 and 1400 MLT. The results suggest that including wave particle interactions beyond geostationary orbit could be very important for global radiation belt models.
International audienceThe main target of the Cluster inner magnetosphere campaign (July-October 2... more International audienceThe main target of the Cluster inner magnetosphere campaign (July-October 2013) is to identify linear and nonlinear processes that affect EMIC, equatorial magnetosonic and chorus waves. The present study examines equatorial magnetosonic waves that are regularly observed under the arch of the plasmasphere, due to the formation of a natural waveguide like structure. These waves are usually observed in the frequency range from a few tens to hundreds of Hz. The spectrum exhibits a banded structure whose spacing is of the order of the ion gyrofrequency in the source region. This fine structure results in complications for the identification of the wave dispersion using data from multispacecraft separated by distances of around 10-100 km. It is shown how this complication can be resolved. The resulting dispersion of the observed waves is presented and compared with analytical solutions
Intense kHz waves generated by electron cyclotron resonance are often observed by the STAFF instr... more Intense kHz waves generated by electron cyclotron resonance are often observed by the STAFF instrument on the TC-1 Double Star spacecraft These electromagnetic waves with frequencies below fce are thought to be associated with the diffuse aurora together with higher frequency electrostatic electron cyclotron harmonic waves As part of the DWP instrumentation on board the Double Star Equator TC-1 spacecraft
Plasma emissions, electromagnetic or electrostatic, are very good tracers of the phenomena occuri... more Plasma emissions, electromagnetic or electrostatic, are very good tracers of the phenomena occuring in space plasma. The Whisper instruments on board each of the Cluster spacecraft regularly monitor the plasma waves related to the plasma dynamics in the various regions of the magnetosphere such as the cusp, entry layer, magnetosheath, magnetopause, plasmasheet and its boundary layer, or plasmapause. Although most of these signatures have already been observed by past missions, the good sensitivity, time and frequency resolution of Whisper, combined with the vantage of the four viewpoints, allow new insight into the plasma mechanisms at their origin, locally or remotely. The most significant observations collected so far by Whisper, with supporting data from other wave instruments, both at close (100 km) and large (above 2000 km) spacecraft separations will be presented and discussed.
Journal of Geophysical Research: Space Physics, 2010
Broadband electrons (BBEs) exhibit remarkable electron flux enhancements over a broad energy rang... more Broadband electrons (BBEs) exhibit remarkable electron flux enhancements over a broad energy range (0.03–30 keV) near the equatorward edge of the auroral oval during geomagnetic storms. Here, we report a BBE event observed by the Fast Auroral Snapshot (FAST) satellite at 1355–1359 UT, ∼61°–66° invariant latitudes, ∼0600 magnetic local time (MLT), and ∼3800 km altitude during a storm on 25 July 2004. The Double Star (DS) TC1 satellite was located near the magnetic equator at L = 5.7, close to the same local time as FAST. We investigate the acceleration process of BBEs from the inner magnetosphere to near the ionosphere by comparing electron data obtained by FAST and DS TC1. We also investigate both plasma and field variations in the inner magnetosphere associated with substorm onset using DS TC1 data to examine the relationship between the BBEs and the storm time substorm. Ground geomagnetic field data show a positive H‐bay at ∼1349 UT at ∼0600 MLT, indicating that a storm time subst...
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Papers by K. Yearby