Publications (41)20.18 Total impact
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Article: Wind Spacecraft Observations of Solar Impulsive Electron Events Associated with Solar Type III Radio Bursts
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ABSTRACT: We present Wind spacecraft observations of solar impulsive electron events associated with locally generated Langmuir waves during solar type III radio bursts. The solar impulsive electrons had energies from ~600 eV to greater than 300 keV. Local Langmuir emissions associated with these fluxes generally coincided with the arrival of 2-12 keV electrons. A survey of 27 events over 1 yr shows that there were few occurrences of electron distributions (~96 s averaged) that were unstable to Langmuir waves and none that had a substantial growth rate (>3 × 10-2 s-1) or endured for more than 96 s. Intense solar impulsive electron events that occurred on 1995 April 2 are studied in detail. Marginally stable (plateaued) distributions occasionally coincided with a periods of local Langmuir emissions, but the electron distributions were otherwise stable. These observations suggest that kinetic processes were modifying the electron distribution but also suggest that processes other than one-dimensional quasilinear relaxation were involved. We find that solar impulsive electron distributions were often unstable to oblique waves, such as quasi-electrostatic whistler waves or electromagnetic ion cyclotron waves, suggesting that competition between Langmuir and oblique emissions may be important. There are several other features in the Wind spacecraft solar impulsive electron observations that are noteworthy. Nondispersive flux modulations were visible in many of the events (also visible in the published ISEE 3 data) in ~1-4 keV electrons, suggesting that a local hydromagnetic instability may have accompanied the lowest energy solar impulsive electron fluxes. The Wind data differ from the ISEE 3 data in the energy spectra of the electron events. ISEE 3 recorded few events with only high-energy (>10 keV) electron fluxes, whereas a survey of the Wind events shows a substantially higher ratio of high-energy events. The high-energy events were often associated with solar flares that could not have been magnetically well connected with the satellite.The Astrophysical Journal 01/2009; 503(1):435. · 6.02 Impact Factor -
Article: Kinetic signatures during a quasi-continuous lobe reconnection event: Cluster Ion Spectrometer (CIS) observations
Journal of Geophysical Research (Space Physics). 09/2006; 111:9212. -
Article: Energetic magnetospheric oxygen in the magnetosheath and its response to IMF orientation: Cluster observations
Journal of Geophysical Research (Space Physics). 07/2004; 109:7203. -
Article: Bow shock specularly reflected ions in the presence of low-frequency electromagnetic waves: a case study
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ABSTRACT: An energetic ion ( E =40) event observed by the CLUSTER/CIS experiment upstream of the Earth's bow shock is studied in detail. The ion event is observed in association with quasi-monochromatic ULF MHD-like waves, which we show modulate the ion fluxes. According to three statistical bow shock position models, the Cluster spacecrafts are located at ~0.5 R<sub>e</sub> from the shock and the averaged bow shock ?<sub> Bn0 </sub> is about ~30°. The analysis of the three-dimensional angular distribution indicates that ions propagating roughly along the magnetic field direction are observed at the onset of the event. Later on, the angular distribution is gyrophase-bunched and the pitch-angle distribution is peaked at a<sub>0</sub>~?<sub> Bn0 </sub>, consistent with the specular reflection production mechanism. The analysis of the waves shows that they are left-handed in the spacecraft frame of reference (right-handed in the solar wind frame) and propagate roughly along the ambient magnetic field; we have found that they are in cyclotron-resonance with the field-aligned beam observed just upstream. Using properties of the waves and particles, we explain the observed particle flux-modulation in the context of ?<sub> Bn </sub> changes at the shock caused by the convected ULF waves. We have found that the high count rates coincide with particles leaving the shock when ?<sub> Bn </sub> angles are less than ~40°, consistent with the specular reflection hypothesis as the production mechanism of ions.01/2004; -
Article: Case studies of the dynamics of ionospheric ions in the Earth's magnetotail
Journal of Geophysical Research (Space Physics). 01/2004; 109:1212. -
Article: Bow Shock Specular Reflected Ions in Presence of Low Frequency Electromagnetic Waves: a Case Study
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ABSTRACT: An energetic ion event observed by CLUSTER CIS experiment upstream of the Earth's bow shock is studied in detail. The ion event is observed in association with quasi-monochromatic ULF MHD-like waves which modulate the ion fluxes. According to three statistical bow shock position models, the Cluster spacecraft are located at about .5 RE from the shock and the averaged bow shock θBN is about 30°. The analysis of the three-dimensional angular distribution indicates that ions propagating roughly along the magnetic field direction are observed at the onset of the event. Later on the angular distribution is gyrophase-bunched and the pitch-angle distribution is peaked at α0 ~ θBN consistent with the specular reflection production mechanism. The analysis of the waves shows that they are left-handed in the spacecraft frame and propagate roughly along the ambient magnetic field; we have found that they are in cyclotron resonance with the field-aligned beam observed just upstream. Using the waves and particles properties we explain the observed particle flux-modulation in term of θBN changes at the shock due to the low frequency waves and therefore consistent with the specular reflection hypothesis as the source of ions.AGU Fall Meeting Abstracts. 11/2002; -1:0550. -
Article: Turbulence in the solar wind as seen by Cluster CIS experiment: preliminary results on intermittency and scaling laws
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ABSTRACT: One of the most interesting features of solar wind turbulence is the intermittent character of its velocity fluctuations. A direct consequence of this would imply that small eddies are less and less space filling if turbulence is looked at in the framework of a classical Richardson's cascade. This phenomenon would cause solar wind turbulence to be intermittently distributed in space. In other words, the global scale invariance required in the K41 theory would release towards a local scale invariance where different fractal sets characterized by different scaling exponents can be found. The first solar wind plasma measurements made by the CIS experiment onboard Cluster spacecraft reveal the existence of some differences of the intermittent character of the fluctuations as observed by two different spacecraft. Although these findings are based on a preliminary analysis and expect to be confirmed by a similar analysis performed on magnetic field data, our study fully confirms previous findings reported in literature that ascribe to the presence of the border between adjacent flux tubes an important role in the intermittency of solar wind fluctuations.02/2002; 477:361-364. -
Article: Multi-spacecraft observations of the CPS and PSBL using the CIS instruments on CLUSTER
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ABSTRACT: We present multi-spacecraft observations of the Central Plasma Sheet (CPS) and the Plasma Sheet Boundary Layer (PSBL) as observed by the CIS-CODIF instrument on CLUSTER. During these passes the spacecraft have apogee (XGSE ~20 Re) in the midnight region. The CIS-CODIF instrument measured ion distribution functions of the major species, H+, He++, He+ and O+ over the energy range 20 eV - 40 keV. In this study we focus in the presence of earthward and tailward ion beams and flows in the CPS and PSBL where two types of ion populations were observed. Earthward ion flows at energies 1 keV - 10 keV and low energy (< ~100 eV) field aligned ions coming from the Earth with the O+ ions appearing predominately as field aligned tailward beams. The composition and directional information will be used to infer the source of the CPS and PSBL plasma. During the comissioning phase (September 2000) the spacecraft crossed the night side plasma sheet with a separation of ~600 km, while the current (September 2001) separation is ~2000 km. This bigger separation seems to be necessary (in contrast to the smaller separation) for the distinction between spatial and temporal structures.AGU Fall Meeting Abstracts. 11/2001; -1:0812. -
Article: Comparison of plasma sheet dynamics during pseudobreakups and expansive aurorae
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ABSTRACT: Global auroral images and plasma sheet ion distributions and magnetic field data are examined for two intervals when the Ultraviolet Imager (UVI) onboard the Polar spacecraft was imaging the entire northern auroral oval and, at the same time, the Wind spacecraft was passing through the near-Earth plasma sheet. On 26 July 1997, UVI recorded a series of brief, localized auroral brightenings known as pseudobreakups. On 27 March 1996, UVI observed several global expansions of auroral activity. Large variations in the magnetic field were observed by the Wind magnetometer, large velocity moments were derived from Wind ion measurements, and ions were accelerated to mega-electron-volt energies during both types of activity. The plasma sheet dynamics appear very similar during these two different types of auroral activities. Closer inspection of the ion distribution functions and energy spectra indicate that the plasma sheet dynamics need to be characterized kinetically. © 2001 American Institute of Physics.Physics of Plasmas 03/2001; 8(4):1127-1132. · 2.15 Impact Factor -
Article: Kinetic Characterization of Plasma Sheet Dynamics
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ABSTRACT: The Wind spacecraft made 26 perigee passes through the near-earth plasma sheet region during 1994 to 1997. Nearly all of these passes obtained plasma data from substorms and bursty bulk flow (BBF) events. New features of ion distributions have been observed in both the plasma sheet boundary layer (PSBL) and the central plasma sheet (CPS) in the vicinity of the current sheet that are relevant for understanding the structure of the PSBL and the mechanisms of particle acceleration to MeV energies associated with the BBF events. Kinetic processes are key to understanding these new observations that are not adequately explained by existing magnetohydrodynamics (MHD) models and theories. This article will feature the phase space distribution functions as the primary data product. The main purpose of this article is to establish an observational framework for new improved models and theories. The new observations should challenge modelers and theorists.Space Science Reviews 12/2000; 95(1):237-255. · 3.61 Impact Factor -
Article: Plasma Behavior during Pseudobreakup and Expansive Aurorae
06/2000; 443:235. -
Article: Evidence for interplanetary magnetic field B-y controlled large-scale reconnection at the dayside magnetopause
Journal of Geophysical Research-Space Physics. 01/2000; 105(A12):27497-27507. -
Article: Observations of Substorms from the Auroral Ionosphere to the Distant Plasma Sheet
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ABSTRACT: We have been studying how substorms work by examining the global polar Ultraviolet Imager (UVI) images in correlation with observations from the ground, interplanetary space and the geomagnetic tail between 10-20 earth radii. One of the objectives of our study is to better understand the connection among many complex phenomena going on close to Earth and those in the distant plasma sheet. We have studied, for example, how the aurora[ and polar cap boundaries at different local times behave in relation to variations observed in the solar wind and plasma sheet during substorms. Preliminary results indicate that the polar cap and auroral oval boundaries expand and contract in a complicated but systematic way. These variations are correlated to solar wind parameters, and thinning and recovery phenomena in the plasma sheet. These results will be presented and interpreted in terms of directly driven and/or unloading substorm processes.02/1998; -
Article: Does the UVI on Polar Detect Cosmic Snowballs?
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ABSTRACT: Frank and Sigwarth [1997a] claim that the dark pixels observed in dayglow images obtained by the Earth sensor of the Visible Imaging System (VIS) are due to bombardment of Earth by 20 to 40 ton cosmic snowballs. We have independently studied the same one hour of VIS data Frank and Sigwarth used and have performed detailed statistical analysis of the dark pixels. The characteristics of the dark pixels from the VIS images have been compared to those obtained from the overlapping images from the Ultraviolet Imager (UVI). We find the occurrence distributions of the dark pixels, single and multiple, from VIS and UVI are nearly identical. This result cannot be explained by a -eophysical source since the two cameras have different pixel resolutions: A search for evidence of of spacecraft "wobble" motion, whose presence would indicate that the source is external to the camera, has found that pairs of dark pixel clusters are uniformly distributed in an-le and no preference is observed in the wobble direction. Instrument artifacts as the source of the dark pixels is the most likely explanation for these results. Probability estimates for the occurrence of dark pixel clusters lead us to expect coincident events of instrumental origin to occur frequently in the two cameras. The conclusion of this study is that neither VIS nor UVI provide any scientific evidence that the origin of dark pixels is geophysical.02/1998; -
Article: Understanding Substorms from the Auroral Ionosphere to the Distant Plasma Sheet
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ABSTRACT: The global polar UVI images have been correlated with observations from the ground, ionosphere, geomagnetic tail between 10-20 earth radii and the interplanetary space. One of the objectives of our study is to better understand the connection among many complex phenomena occurring close to Earth and those in the near--earth plasma sheet. We have examined the details of how the auroral and polar cap boundaries at different local times behave in relation to variations occurring in the solar wind, ionosphere and plasma sheet during substorms. We have also compared locations of boundaries deduced from images to electron flux "boundaries" observed by polar orbiting spacecraft. Our results indicate that the ionospheric dynamics is important and polar cap and auroral oval boundaries expand and contract in a complicated but systematic way. These variations are correlated to solar wind parameters and growth and recovery phenomena in the plasma sheet. These results can be interpreted in terms of directly driven and/or unloading substorm processes.02/1998; -
Article: The Relationship of Ion Beams and Fast Flows in the Plasma Sheet Boundary Layer
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ABSTRACT: We report new findings on the behavior of plasmas in the vicinity of the plasma sheet boundary layer (PSBL). A large geometrical factor detector on WIND (3D plasma experiment) has discovered a unidirectional ion beam streaming in the tailward direction missed by previous observations. This tailward beam is as intense as the earthward streaming beam and it is found just inside the outer edge of the PSBL where earthward streaming beams are observed. The region where this tailward beam is observed includes an isotropic plasma component which is absent in the outer edge where earthward streaming beams are found. When these different distributions are convolved to calculate the velocity moments, fast flows (greater than 400 km/s) result in the earthward direction and much slower flows (less than 200 km/s) in the tailward direction. These new findings are substantially different from previous observations. Thus, the interpretation of fast flows and earthward and counterstreaming ion beams in terms of a neutral line model must be reexamined.02/1998; -
Article: Does the Ultraviolet Imager on Polar Detect Cometesimals?
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ABSTRACT: The Earth's dayglow images obtained by the Ultraviolet Imager (UVI) on Polar should show darkened pixels if cometesimals bombard Earth. This darkening occurs because the UV emissions are absorbed by water between the altitude where the dayglow emissions are produced and the Polar spacecraft. We have asked: (1) Does the UVI detect darkened pixels? (2) If so, what are their characteristics? (3) What can the UVI say about the presence/absence of cometesimals? The UVI does see dark pixels, which tend to be clustered. But the calibration data obtained from the same instrument just before the instrument was launched show similarly darkened pixel clusters. After a though statistical analysis of these images, we conclude that the darkened pixels are instrumental artifacts. Therefore, the UVI does not provide evidence for the existence of the cometesimals.02/1997; -
Article: THE CLUSTER ION SPECTROMETRY (CIS) EXPERIMENT
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ABSTRACT: The Cluster Ion Spectrometry (CIS) experiment is a comprehensive ionic plasma spectrometry package on-board the four Cluster spacecraft capable of obtaining full three-dimensional ion distributions with good time resolution (one spacecraft spin) with mass per charge composition determination. The requirements to cover the scientific objectives cannot be met with a single instrument. The CIS package therefore consists of two different instruments, a Hot Ion Analyser (HIA) and a time-of-flight ion COmposition and DIstribution Function analyser (CODIF), plus a sophisticated dual-processor-based instrument-control and Data-Processing System (DPS), which permits extensive on-board data-processing. Both analysers use symmetric optics resulting in continuous, uniform, and well-characterised phase space coverage. CODIF measures the distributions of the major ions (H+, He+, He++, and O+) with energies from ~0 to 40 keV/e with medium (22.5) angular resolution and two different sensitivities. HIA does not offer mass resolution but, also having two different sensitivities, increases the dynamic range, and has an angular resolution capability (5.6 5.6) adequate for ion-beam and solar-wind measurements.Space Science Reviews 12/1996; 79(1):303-350. · 3.61 Impact Factor -
Article: Observations of the 3-D distribution of interplanetary electrons and ions from solar wind plasma to low energy cosmic rays
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ABSTRACT: The 3-D Plasma and Energetic Particle instrument on the GGS Wind spacecraft (launched November 1, 1994) is designed to make measurements of the full three-dimensional distribution of suprathermal electrons and ions from solar wind plasma to low energy cosmic rays, with high sensitivity, wide dynamic range, good energy and angular resolution, and high time resolution. Three pairs of double-ended telescopes, each with two or three closely sandwiched passivated ion implanted silicon detectors measure electrons and ions from approximately 20 keV to greater than or equal to 300 keV. Four top-hat symmetrical spherical section electrostatic analyzers with microchannel plate detectors, a large and a small geometric factor analyzer for electrons and a similar pair for ions, cover from approximately 3 eV to 30 keV. We present preliminary observations of the electron and ion distributions in the absence of obvious solar impulsive events and upstream particles. The quiet time electron energy spectrum shows a smooth approximately power law fall-off extending from the halo population at a few hundred eV to well above approximately 100 keV The quiet time ion energy spectrum also shows significant fluxes over this energy range. Detailed 3-D distributions and their temporal variations will be presented.07/1995; -
Article: A three-dimensional plasma and energetic particle investigation for the wind spacecraft
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ABSTRACT: This instrument is designed to make measurements of the full three-dimensional distribution of suprathermal electrons and ions from solar wind plasma to low energy cosmic rays, with high sensitivity, wide dynamic range, good energy and angular resolution, and high time resolution. The primary scientific goals are to explore the suprathermal particle population between the solar wind and low energy cosmic rays, to study particle accleration and transport and wave-particle interactions, and to monitor particle input to and output from the Earth's magnetosphere.Three arrays, each consisting of a pair of double-ended semi-conductor telescopes each with two or three closely sandwiched passivated ion implanted silicon detectors, measure electrons and ions above 20 keV. One side of each telescope is covered with a thin foil which absorbs ions below 400 keV, while on the other side the incoming 1 MeV) and ions (up to 11 MeV) are identified by the two double-ended telescopes which have a third detector. The telescopes provide energy resolution of E/E0.3 and angular resolution of 22.536, and full 4 steradian coverage in one spin (3 s).Top-hat symmetrical spherical section electrostatic analyzers with microchannel plate detectors are used to measure ions and electrons from 3 eV to 30 keV. All these analyzers have either 180 or 360 fields of view in a plane, E/E0.2, and angular resolution varying from 5.6 (near the ecliptic) to 22.5. Full 4 steradian coverage can be obtained in one-half or one spin. A large and a small geometric factor analyzer measure ions over the wide flux range from quiet-time suprathermal levels to intense solar wind fluxes. Similarly two analyzers are used to cover the wide range of electron fluxes. Moments of the electron and ion distributions are computed on board.In addition, a Fast Particle Correlator combines electron data from the high sensitivity electron analyzer with plasma wave data from the WAVE experiment (Bougeretet al., in this volume) to study wave-particle interactions on fast time scales. The large geometric factor electron analyzer has electrostatic deflectors to steer the field of view and follow the magnetic field to enhance the correlation measurements.Space Science Reviews 01/1995; 71(1):125-153. · 3.61 Impact Factor
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Institutions
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2001–2009
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University of Washington Seattle
- Department of Earth and Space Sciences
Seattle, WA, USA
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