Papers by Pierrette Decreau
HAL (Le Centre pour la Communication Scientifique Directe), Apr 20, 2005
We briefly present observations of nonthermal continuum (NTC) radiations obtained close to the so... more We briefly present observations of nonthermal continuum (NTC) radiations obtained close to the sources at the plasmapause by the Whisper instruments on Cluster. The examples considered illustrate the variety of the characteristics of the NTC such as the overall bandwidth of the emissions. The omnipresent multiple narrow bandwidth components are further evidence that the emissions could be generated from multiple, closely spaced, short scale regions (a few 10 km).
HAL (Le Centre pour la Communication Scientifique Directe), Aug 21, 2016
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
HAL (Le Centre pour la Communication Scientifique Directe), Sep 1, 2005
Intense and localized burst of electrostatic emissions have been observed by the Whisper instrume... more Intense and localized burst of electrostatic emissions have been observed by the Whisper instrument on Cluster at frequency close to the electron plasma frequency, in the magnetopause boundary layer. The good time resolution of Whisper when in burst mode telemetry as well as the combination of the observations performed by the four Cluster spacecraft at short separation distance (~100 km) have allowed to determine in one case the dimension of these structure, typically a few tens of kilometers, close to the electron scale. We browse Whisper data in search for such events and present here some examples of their observations. We present the main characteristics of the spectra and power profile of the emissions.
Annales Geophysicae, Nov 29, 2007
We use whistler waves observed close to the magnetopause as an instrument to investigate the inte... more We use whistler waves observed close to the magnetopause as an instrument to investigate the internal structure of the magnetopause-magnetosheath boundary layer. We find that this region is characterized by tube-like structures with dimensions less than or comparable with an ion inertial length in the direction perpendicular to the ambient magnetic field. The tubes are revealed as they constitute regions where whistler waves are generated and propagate. We believe that the region containing tube-like structures extend several Earth radii along the magnetopause in the boundary layer. Within the presumed wave generating regions we find current structures moving at the whistler wave group velocity in the same direction as the waves.
Nonlinear Processes in Geophysics, Aug 10, 2006
We study plasma transport at a thin magnetopause (MP), described hereafter as a thin current shee... more We study plasma transport at a thin magnetopause (MP), described hereafter as a thin current sheet (TCS), observed by Cluster at the southern cusp on 13 February 2001 around 20:01 UT. The Cluster observations generally agree with the predictions of the Gas Dynamic Convection Field (GDCF) model in the magnetosheath (MSH) up to the MSH boundary layer, where significant differences are seen. We find for the MP a normal roughly along the GSE xaxis, which implies a clear departure from the local average MP normal, a ∼90 km thickness and an outward speed of 35 km/s. Two populations are identified in the MSH boundary layer: the first one roughly perpendicular to the MSH magnetic field, which we interpret as the "incident" MSH plasma, the second one mostly parallel to B. Just after the MP crossing a velocity jet is observed with a peak speed of 240 km/s, perpendicular to B, with M A =3 and β>10 (peak value 23). The magnetic field clock angle rotates by 70 • across the MP. E x is the main electric field component on both sides of the MP, displaying a bipolar signature, positive on the MSH side and negative on the opposite side, corresponding to a ∼300 V electric potential jump across the TCS. The E×B velocity generally coincides with the perpendicular velocity measured by CIS; however, in the speed jet a difference between the two is observed, which suggests the need for an extra flow source. We propose that the MP TCS can act locally as an obstacle for low-energy ions (<350 eV),
Nonlinear Processes in Geophysics, Aug 10, 2006
Proceeding with the analysis of Amata et al. (2005), we suggest that the general feature for the ... more Proceeding with the analysis of Amata et al. (2005), we suggest that the general feature for the local transport at a thin magnetopause (MP) consists of the penetration of ions from the magnetosheath with gyroradius larger than the MP width, and that, in crossing it, the transverse potential difference at the thin current sheet (TCS) is acquired by these ions, providing a field-particle energy exchange without parallel electric fields. It is suggested that a part of the surface charge is self-consistently produced by deflection of ions in the course of inertial drift in the nonuniform electric field at MP. Consideration of the partial moments of ions with different energies demonstrates that the protons having gyroradii of roughly the same size or larger than the MP width carry fluxes normal to MP that are about 20% of the total flow in the plasma jet under MP. This is close to the excess of the ion transverse velocity over the cross-field drift speed in the plasma flow just inside MP (Amata et al., 2005), which conforms to the contribution of the finite-gyroradius inflow across MP. A linkage through the TCS between different plasmas results from the momentum conservation of the
Annales Geophysicae, Dec 23, 2005
Whistler emissions close to the magnetopause on the magnetospheric side are investigated using th... more Whistler emissions close to the magnetopause on the magnetospheric side are investigated using the four Cluster spacecraft. The waves are found to be generated in thin (electron-scale) sheets moving with the plasma drift velocity. A feature in the electron data coincides with the waves; hot magnetospheric electrons disappear for a few satellite spins. This produces or enhances a temperature anisotropy, which is found to be responsible for the generation of the whistler mode waves. The high energy electrons are thought to be lost through the magnetopause and we suggest that the field lines, on which the waves are generated, are directly connected to a reconnection diffusion region at the magnetopause.
Annales Geophysicae, Nov 6, 2007
The interaction of the solar wind with the Earth magnetosphere generates a broad variety of plasm... more The interaction of the solar wind with the Earth magnetosphere generates a broad variety of plasma waves through different mechanisms. The four Cluster spacecraft allow one to determine the regions where these waves are generated and their propagation directions. One of the tools which takes full advantage of the multi-point capabilities of the Cluster mission is the wave telescope technique which provides the wave vector using a plane wave representation. In order to determine the distance to the wave sources, the source locator-a generalization of the wave telescope to spherical waves-has been recently developed. We are applying the source locator to magnetic field data from a typical traversal of Cluster from the cusp region and the outer magnetosphere into the magnetosheath and the near Earth solar wind. We find a high concentration of low frequency wave sources in the electron foreshock and in the cusp region. To a lower extent, low frequency wave sources are also found in other magnetospheric regions.
Journal Of Geophysical Research: Space Physics, Mar 1, 2021
• We have applied self-learning methods to predict the key plasma regions crossed by the 10 CLUST... more • We have applied self-learning methods to predict the key plasma regions crossed by the 10 CLUSTER-II spacecraft in the Earth magnetosphere using the WHISPER instrument 11 • The extraction of the thermal electron density from WHISPER active (sounding mode) 12 and natural (passive mode) electric field spectra is automatically done in the free so-13 lar wind, in the magnetosheath region and in the plasmasphere 14 • Such automatic procedure could be used for future data processing of electric field ex-15 periments onboard space missions (for instance AM 2 P onboard BepiColombo or MIME 16 onboard JUICE)
Journal of Geophysical Research, Jul 1, 2009
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific r... more HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. NonThermal Continuum Radiation Observed from the CLUSTER Fleet Pierrette Décréau, S. Grimald, Michel Parrot, O. Randriamboarison, Jean-Louis Rauch, Jean-Gabriel Trotignon, X. Vallieres, P. Canu, N. Cornilleau, J. Pickett, et al.
AIP Conference Proceedings, 2007
Larmor size transient structures with depletions as large as 99% of ambient solar wind density le... more Larmor size transient structures with depletions as large as 99% of ambient solar wind density levels occur commonly upstream of Earth's coUisionless bow shock. These "density holes" have a mean duration of-17.9 ± 10.4s but holes as short as 4s have been observed. The average fractional density depletion (5n/n) inside the holes is-0.68 ± 0.14. The density of the upstream edge moving in the sunward direction can be enhanced by five or more times the solar wind density. Particle distributions show the steepened edge can behave like a shock, and measured local field geometries and Mach number support this view. Similarly shaped magnetic holes accompany the density holes indicating strong coupling between fields and particles. The density holes are only observed with upstream particles, suggesting that back-streaming particles interacting with the solar wind are important.
Space Sciences Series of ISSI, 2005
A mechanism of chorus generation was suggested by V. Yu. Trakhtengerts (1999) on the basis of the... more A mechanism of chorus generation was suggested by V. Yu. Trakhtengerts (1999) on the basis of the backward wave oscillator (BWO) regime of magnetospheric cyclotron maser. According to this mechanism, a succession of whistler wave packets is generated in a small near equatorial region owing to the absolute instability of whistler-mode waves in the presence of a step-like distribution function
Nonlinear Processes in Geophysics, 2005
Nonlinear Processes in Geophysics, 2004
We report on recent measurements of solitary waves made by the Wideband Plasma Wave Receiver loca... more We report on recent measurements of solitary waves made by the Wideband Plasma Wave Receiver located on each of the four Cluster spacecraft at 4.5-6.5 R E (well above the auroral acceleration region) as they cross field lines that map to the auroral zones. These solitary waves are observed in the Wideband data as isolated bipolar and tripolar waveforms. Examples of the two types of pulses are provided. The time durations of the majority of both types of solitary waves observed in this region range from about 0.3 up to 5 ms. Their peak-to-peak amplitudes range from about 0.05 up to 20 mV/m, with a few reaching up to almost 70 mV/m. There is essentially no potential change across the bipolar pulses. There appears to be a small, measurable potential change, up to 0.5 V, across the tripolar pulses, which is consistent with weak or hybrid double layers. A limited cross-spacecraft correlation study was carried out in order to identify the same solitary wave on more than one spacecraft. We found no convincing correlations of the bipolar solitary waves. In the two cases of possible correlation of the tripolar pulses, we found that the solitary waves are propagating at several hundred to a few thousand km/s and that they are possibly evolving (growing, decaying) as they propagate from one spacecraft to the next. Further, they have a perpendicular (to the magnetic field) width of 50 km or greater and a parallel width of about 2-5 km. We conclude, in general,
Nonlinear Processes in Geophysics, 2009
Electrostatic Solitary Waves (ESWs) have been observed by several spacecraft in the current layer... more Electrostatic Solitary Waves (ESWs) have been observed by several spacecraft in the current layers of Earth's magnetosphere since 1982. ESWs are manifested as isolated pulses (one wave period) in the high time resolution waveform data obtained on these spacecraft. They are thus nonlinear structures generated out of nonlinear instabilities and processes. We report the first observations of ESWs associated with the onset of a super-substorm that occurred on 24 August 2005 while the Cluster spacecraft were located in the magnetotail at around 18-19 R E and moving northward from the plasma sheet to the lobes. These ESWs were detected in the waveform data of the WBD plasma wave receiver on three of the Cluster spacecraft. The majority of the ESWs were detected about 5 min after the super-substorm onset during which time 1) the PEACE electron instrument
Journal of Geophysical Research: Space Physics, 1993
Data acquired during several multiday periods in 1982 at ground stations Siple, Halley, and Kergu... more Data acquired during several multiday periods in 1982 at ground stations Siple, Halley, and Kerguelen and on satellites DE 1, ISEE 1, and GEOS 2 have been used to investigate thermal plasma structure and dynamics in the duskside plasmasphere bulge region of the Earth. The distribution of thermal plasma in the dusk bulge sector is difficult to describe realistically, in part because of the time integral manner in which the thermal plasma distribution depends upon the effects of bulk cross-B flow and interchange plasma flows along B. While relatively simple MHD models can be useful for qualitatively predicting certain effects of enhanced convection on a quiet plasmasphere, such as an initial sunward entrainment of the outer regions, they are of limited value in predicting the duskside thermal plasma structures that are observed. Furthermore, use of such models can be misleading if one fails to realize that they do not address the question of the formation of the steep plasmapause profile or provide for a possible role of instabilities or other irreversible processes in plasmapause formation. Our specific findings, which are based both upon the present case studies and upon earlier work, include the following: (1) during active periods the plasmasphere appears to become divided into two entities, a main plasmasphere and a duskside bulge region. The latter consists of outlying or outward extending plasmas that are the products of erosion of the main plasmasphere; (2) in the aftermath of an increase in convection activity, the main plasmasphere tends (from a statistical point of view) to become roughly circular in equatorial cross section, with only a slight bulge at dusk; (3) the abrupt westward edge of the duskside bulge observed from whistlers represents a state in the evolution of sunward extending streamers; (4) in the aftermath of a weak magnetic storm, 10 to 30% of the plasma "removed" from the outer plasmasphere appears to remain in the afternoon-dusk sector beyond the main plasmasphere. This suggests that plasma flow from the afternoon-dusk magnetosphere into the boundary layers is to some extent impeded, possibly through a mechanism that partially decouples the high altitude and ionospheric-level flow regimes; (5) outlying dense plasma structures may circulate in the outer duskside magnetosphere for many days following an increase in convection, unless there is extremely deep quieting; (6) a day-night plasmatrough boundary may be identified in equatorial satellite data; (7) factor-of-2-to-10 density irregularities appear near the plasmapause in the postdusk sector in the aftermath of weak magnetic storms; (8) during the refilling of the plasmatrough from the ionosphere at oe = 4.6, predominantly bidirectional field aligned and equatorially trapped light ion pitch angle distributions give way to a predominantly isotropic distribution (as seen by DE 1) when the plasma density reaches a level a factor of about 3 below the saturated plasmasphere level; (9) some outlying dense plasma structures are effectively detached from the main plasmasphere, while others appear to be connected to that body. eastward flow (in a stationary frame) to predominantly westward et al., 1992]. The distribution of magnetospheric plasmas at any time is dependent upon the convection activity, the instabilities, flow. And by analogy to the midlatitude trough, the bulge may and the magnetosphere-ionosphere interchange fluxes to which the contain adjacent plasma regions whose preceding flow histories individual plasma packets have previously been exposed. This differ widely. The duskside bulge region is considered to be geoperspective seems of particular importance in studies of the dusk-physically important because of its apparent involvement in the side bulge region of the plasmasphere, a region that today remains erosion of the plasmasphere by the action of enhanced convection electric fields [e.g., Chappell, 1972] and because of interactions
Journal of Geophysical Research: Space Physics, 2012
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
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Papers by Pierrette Decreau