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Global Positioning System (GPS) L1 amplitude data, obtained using the Canadian High Arctic Ionospheric Network (CHAIN) during the period 2008–2018, is used to study the seasonal and solar cycle dependence of high‐latitude amplitude... more
Global Positioning System (GPS) L1 amplitude data, obtained using the Canadian High Arctic Ionospheric Network (CHAIN) during the period 2008–2018, is used to study the seasonal and solar cycle dependence of high‐latitude amplitude scintillation. The occurrence of amplitude scintillation is predominantly confined to the 10–18 magnetic local time (MLT) and 72–87° Altitude‐Adjusted Corrected Geomagnetic (AACGM) sector and is a winter and equinoctial phenomenon. The occurrence of amplitude scintillation shows a clear seasonal and solar cycle dependence with a maximum value of ∼11% during the high solar activity early winter periods, and a secondary maximum in equinoctial months, and almost no occurrence during summer months. This pattern in occurrence suggests that amplitude scintillation is a phenomenon that is closely associated with the presence of patches and particle precipitation events.
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Electron velocity distributions in Mars's magnetosheath show a systematic erosion of the energy spectrum with distance downstream from the bow shock. Previous attempts to model this erosion invoked assumptions to promote electron... more
Electron velocity distributions in Mars's magnetosheath show a systematic erosion of the energy spectrum with distance downstream from the bow shock. Previous attempts to model this erosion invoked assumptions to promote electron ionization impact collisions with Mars's neutral hydrogen exosphere. We show that the near collision‐free magnetosheath requires a kinetic description; the population of electrons at any location is a convolution of electrons arriving from more distant regions that ultimately map directly to the solar wind. We construct a simple model that captures all the essential physics. The model demonstrates how the erosion of the electron distributions is the result of the trapping, escape, and replacement of electrons that traverse the global bow shock; some are temporarily confined to the expanding cavity formed by the cross‐shock electrostatic potential. The model also has implications for the ability of solar wind electrons to reach altitudes below the pi...
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Backstreaming electrons emanating from the bow shock of Mars reported from the Mars Atmosphere and Volatile EvolutioN/Solar Wind Electron Analyzer observations show a flux fall off with the distance from the shock. This feature is not... more
Backstreaming electrons emanating from the bow shock of Mars reported from the Mars Atmosphere and Volatile EvolutioN/Solar Wind Electron Analyzer observations show a flux fall off with the distance from the shock. This feature is not observed at the terrestrial foreshock. The flux decay is observed only for electron energy E ≥ 29 eV. A reported recent study indicates that Mars foreshock electrons are produced at the shock in a mirror reflection of a portion of the solar wind electrons. In this context, and given that the electrons are sufficiently energetic to not be affected by the interplanetary magnetic field fluctuations, the observed flux decrease appears problematic. We investigate the possibility that the flux fall off with distance results from the impact of backstreaming electrons with Mars exospheric neutral hydrogen. We demonstrate that the flux fall off is consistent with the electron‐atomic hydrogen impact cross section for a large range of energy. A better agreement i...
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Different types of backstreaming ion distributions have been reported in the region upstream from the Earth's bow shock and magnetically connected to it (ion foreshock): field-aligned beams (FABs), gyrating ion and diffuse ion... more
Different types of backstreaming ion distributions have been reported in the region upstream from the Earth's bow shock and magnetically connected to it (ion foreshock): field-aligned beams (FABs), gyrating ion and diffuse ion distributions. Contrary to the first type, the two others are always associated with ULF waves. Among them, gyrating ions with well-defined pitch-angle and gyrophase organization around the local magnetic field have been frequently observed in association with large amplitude quasi-monochromatic right-hand mode waves. These waves reveal the existence of coherent wave-particle interaction which is an efficient process to dissipate the energy of the particles reflected at the collisionless bow shock. It has been shown recently from a large data set from multi-spacecraft observations by Cluster that the gyrophase-bunched ion distributions are mainly produced by such a process from cyclotron-resonant FABs observed just both at the edge of the gyrating ions region and the boundary of ULF waves.
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ABSTRACT
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We report an observation by Cluster-CIS of an energetic (2--30~keV) upstream ion event presenting a clear double-peak spectrum. The lower-energy (E ˜~3.5~keV) peak is associated with an ion beam propagating along the magnetic field... more
We report an observation by Cluster-CIS of an energetic (2--30~keV) upstream ion event presenting a clear double-peak spectrum. The lower-energy (E ˜~3.5~keV) peak is associated with an ion beam propagating along the magnetic field direction, while the higher-energy peak is associated with gyrating ions. Our analysis indicates that the gyrating ions had guiding centers on field lines downstream of the field-aligned component, but that both populations could be sampled simultaneously due to gyroradius effect. We find that downstream limit of the field-aligned beams is populated with protons having a speed 1.5 times the solar wind velocity, which is inconsistent with any known shock-related emission mechanisms. The spatial boundary separating the field-aligned beams from the gyrating ion guiding centers corresponds well with the ULF and intermediate ion foreshock boundary reported in previous studies. Like the field-aligned beams, the gyrating ions reported here have streaming speeds ...
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New features of Earth's bow shock structure have been observed by the HIA ion experiment on the first Chinese scientific satellite, Double Star. At times of coincident apogee, the Cluster spacecraft served as monitors of the upstream... more
New features of Earth's bow shock structure have been observed by the HIA ion experiment on the first Chinese scientific satellite, Double Star. At times of coincident apogee, the Cluster spacecraft served as monitors of the upstream condition providing information from nearly identical instruments. The combination of the orbit with an apogee approximately at 13.5 Re and data obtained in high time resolution (4s) has permitted observations of the shock structure with unprecendented detail. We present examples of laminar and turbulent shocks observed in late February and early March (2004) when the Double Star apogee was located on the sunward side skimming the shock boundary. This talk will discuss (1) evolutionary features of ion distributions of the solar wind slowdown converting almost the entire flow energy into thermal energy, (2) microscopic features that could be signifying kinetic processes at work and (3) ordering of density, bulk velocity and temperature to show the d...
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... The solar wind velocity was ~ 620 km/s. A CIR event which began at 06:35 UT [Mason et al., 1997], had filled the interplanetary medium at ~1 AU ... T| -T|u.) where T| is the ratio of the shock velocity Vs to particle velocity V, and... more
... The solar wind velocity was ~ 620 km/s. A CIR event which began at 06:35 UT [Mason et al., 1997], had filled the interplanetary medium at ~1 AU ... T| -T|u.) where T| is the ratio of the shock velocity Vs to particle velocity V, and p. the cosine of the particle pitch-angle [Decker, 1983 ...
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We report on gyrophase‐restricted ion beams with energies extending from ∼100 keV up to ∼2 MeV, observed by Wind in the Earth's distant (∼65 RE) foreshock. The ion gyrophases seen were nearly constant during periods when the distance... more
We report on gyrophase‐restricted ion beams with energies extending from ∼100 keV up to ∼2 MeV, observed by Wind in the Earth's distant (∼65 RE) foreshock. The ion gyrophases seen were nearly constant during periods when the distance to the shock contact point could be expected to vary by several RE, when there was no significant wave activity. At times the distributions had two peaks ∼180° apart in gyrophase. These were consistent with a remotely‐sensed energetic ion foreshock region having a thickness <2 gyroradii (∼1.5 RE for 0.5 MeV protons with pitch‐angle α = 30°). In this picture, gaps in phase space would correspond to particles with guiding centers outside of the energetic foreshock region. Similar observations over a decade of energies (100 keV–2 MeV) suggest that the region thickness scales with gyroradius. According to this interpretation, we have determined a rough range of geometries for which energetic particle production is favored. (Eg., θBn ∼70–80° for 500 k...
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Foreshock density holes in the context of known upstream plasma structures
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ABSTRACT
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Detailed particle distributions of backstreaming ions observed upstream of the Earth's bow shock by the Cluster Spacecraft are examined. A recent study found that the characteristics of both parallel and perpendicular particle... more
Detailed particle distributions of backstreaming ions observed upstream of the Earth's bow shock by the Cluster Spacecraft are examined. A recent study found that the characteristics of both parallel and perpendicular particle distribution function profiles of field-aligned beams (FABs) are geometry-dependent [Meziane et al., 2007]. FABs observed at oblique shocks have reduced particle distribution functions that exhibit high-energy tails, in contrast to FABs observed at quasi-perpendicular shocks. Gyrating ion as well as diffuse ion populations also show evidence of high energy tails in the reduced distributions. Usually, these tails are satisfactorily fit with a stretched exponential function. It is not clear whether the tails associated with the different populations are related. The existence of these high energy tails raise interesting issues regarding their origin and how they fit with our current outstanding of of backstreaming ions. It is now accepted that the probabilit...
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... on Field-Aligned Beam Distributions K. Meziane, AM Hamza, M. Wilber, MA Lee, C. Mazelle, EA Lucek, T. Hada, and A. Markowitch Abstract We address the unsolved question of how foreshock field-aligned beam (FAB) parallel temperatures... more
... on Field-Aligned Beam Distributions K. Meziane, AM Hamza, M. Wilber, MA Lee, C. Mazelle, EA Lucek, T. Hada, and A. Markowitch Abstract We address the unsolved question of how foreshock field-aligned beam (FAB) parallel temperatures are produced. ...
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Research Interests: Physics and Geophysical
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We present Cluster ion observations obtained at 18 RE in the magnetotail on 1 October 2001. According to a recent analysis, the quartet encountered a reconnection region and a tailward-moving neutral line. We examine in detail selected... more
We present Cluster ion observations obtained at 18 RE in the magnetotail on 1 October 2001. According to a recent analysis, the quartet encountered a reconnection region and a tailward-moving neutral line. We examine in detail selected 3-D ion distributions, which through much of the hour following 0925 UT were non-gyrotropic. B-perpendicular slices of velocity space showed crescent-shaped regions. Occupied