Publication archive

Publication archive

In the book "The Cluster Active Archive - Studying the Earth's Space Plasma Environment", Astrophysics and Space Science Proceedings, H. Laakso et al. (eds.), ISBN 978-90-481-3498-4 (Print) 978-90-481-3499-1 (Online), Springer, 2010

The Chinese National Space Agency (CNSA) Double Star (DSP) spacecraft, TC-1 and TC-2 were launched in December 2003 and July 2004 into near equatorial and polar orbits respectively. During more than 3 years of operations they have maintained a close phasing with the ESA four-spacecraft mission to produce the first, well coordinated multi-scale measurements, sampling phenomena with five and six spacecraft. In this short paper we give a brief review of the DSP mission and show its joint capability with Cluster by showing examples of use of some early and more recent analysis techniques and their application to (more than) four spacecraft. We highlight a selection of some co-ordinated events, focussing on dayside phenomena, but also with a brief discussion of a tail event. Other reviews in this special issue will deal more completely with coverage of the other regions of the magnetosphere.

Published: 04 December 2009
In the book "The Cluster Active Archive - Studying the Earth's Space Plasma Environment", Astrophysics and Space Science Proceedings, H. Laakso et al. (eds.), ISBN 978-90-481-3498-4 (Print) 978-90-481-3499-1 (Online), Springer, 2010

Part of original abstract follows:
At the time of writing, Cluster is approaching 8 years of successful operation and continues to fulfill, if not exceed its scientific objectives. After a nominal mission lifetime of 2 years Cluster currently in its extended mission phase, up to June 2009, with a further extension request submitted for a further 3.5 years. The primary goals of the Cluster mission include three-dimensional studies of small-scale plasma structures and turbulence in the key plasma regions in the Earth's environment: solar wind and bow shock, magnetopause, polar cusps, magnetotail, and auroral zone. During the course of the mission, the relative distance between the four spacecraft is being varied to form a nearly perfect tetrahedral configuration at 100, 250, 600, 2,000, 5,000 and 10,000 km inter-spacecraft separation targeted to study scientifically interesting regions at different scales. In the last few years, the constellation strategy has moved towards a multi-scale concept, enabling two scale sizes to be investigated at the same time. In these cases, three spacecraft are separated by 10,000 km with the last spacecraft separated from this plane by varying distances from 16 km up to several 1,000 km. In this paper, we provide a brief overview of the mission concept and implementation and highlight a number of Cluster's latest science results, which include: the first observation of three dimensional (3-D) surface waves on the bow shock, the first 3-D analysis of turbulence in the magnetosheath, the discovery of magnetosonic waves accelerating electrons to MeV energies in the radiation belts, along with a number of discoveries involving magnetic reconnection.

Published: 04 December 2009
In the book "The Cluster Active Archive - Studying the Earth's Space Plasma Environment", Astrophysics and Space Science Proceedings, H. Laakso et al. (eds.), ISBN 978-90-481-3498-4 (Print) 978-90-481-3499-1 (Online), Springer, 2010

The four-satellite Cluster mission investigates the small-scale structures and physical processes related to interaction between the solar wind and the magnetospheric plasma. The Cluster Active Archive (CAA) (URL: http://caa.estec.esa.int) will contain the entire set of Cluster high-resolution data and other allied products in a standard format and with a complete set of metadata in machine readable format. The total amount of the data files in compressed format is expected to exceed 50 TB. The data archive is publicly accessible and suitable for science use and publication by the world-wide scientific community. The CAA aims to provide user-friendly services for searching and accessing these data and ancillary products. The CAA became operational in February 2006 and as of Summer 2008 has data from most of the Cluster instruments for at least the first 5 years of operations (2001-2005). The coverage and range of products are being continually improved with more than 200 datasets available from each spacecraft, including high-resolution magnetic and electric DC fields and wave spectra; full three-dimensional electron and ion distribution functions from a few eV to hundreds of keV; and various ancillary and browse products to help with spacecraft and event location. The CAA is continuing to extend and improve the online capabilities of the system and the quality of the existing data. It will add new data files for years 2006-2009 and is preparing for the long-term archive with complete coverage after the completion of the Cluster mission.

Published: 04 December 2009
We examine traversals on 20 November 2001 of the equatorial magnetopause boundary layer simultaneously at ~1500 magnetic local time (MLT) by the Geotail spacecraft and at ~1900 MLT by the Cluster spacecraft, which detected rolled-up MHD-scale vortices generated by the Kelvin-Helmholtz instability (KHI) under prolonged northward interplanetary magnetic field conditions. Our purpose is to address the excitation process of the KHI, MHD-scale and ion-scale structures of the vortices, and the formation mechanism of the low-latitude boundary layer (LLBL). The observed KH wavelength (>4 x 104 km) is considerably longer than predicted by the linear theory from the thickness (~1000 km) of the dayside velocity shear layer. Our analyses suggest that the KHI excitation is facilitated by combined effects of the formation of the LLBL presumably through high-latitude magnetopause reconnection and compressional magnetosheath fluctuations on the dayside, and that breakup and/or coalescence of the vortices are beginning around 1900 MLT. Current layers of thickness a few times ion inertia length ~100 km and of magnetic shear ~60° existed at the trailing edges of the vortices. Identified in one such current sheet were signatures of local reconnection: Alfvénic outflow jet within a bifurcated current sheet, nonzero magnetic field component normal to the sheet, and field-aligned beam of accelerated electrons. Because of its incipient nature, however, this reconnection process is unlikely to lead to the observed dusk-flank LLBL. It is thus inferred that the flank LLBL resulted from other mechanisms, namely, diffusion and/or remote reconnection unidentified by Cluster.
Published: 04 December 2009
On 16 March 2005, the Cluster spacecraft crossed a shock almost at the transition between the quasi-perpendicular and quasi-parallel regimes (ThetaBn = 46°) preceded by an upstream low-frequency (~0.02 Hz in the spacecraft frame) wave train observed for more than 10 mn. The wave semicycle nearest to the shock was found to grow in time, steepen and reflect an increasing fraction of the incoming ions. This gives strong indication that this pulsation is becoming a new shock front, standing ~5lambdap upstream of the main front and growing to shock-like amplitude on a timescale of ~35 Omegap. Downstream of the main shock transition, remnants of an older front are found indicating that the reformation is cyclic. This provides a unique example where the dynamics of shock reformation can be sequentially followed. The process shares many characteristics with simulations of reforming quasi-parallel shocks.
Published: 25 November 2009
The variability of energetic electron fluxes (>40 keV) within the plasma sheet is explored using measurements from the Cluster spacecraft from 2001 through 2005. Only cases where the spacecraft remains inside the plasma sheet throughout the event are considered. Interesting cases were found using a combination of automated methods and visual inspection. Events are classified into 4 main types: (1) plasma sheet empty of energetic electrons; (2) decreasing plasma sheet energetic electron fluxes; (3) increasing plasma sheet energetic electron fluxes; and (4) sharp (rising and falling) variations in plasma sheet energetic electron fluxes during a single plasma sheet crossing. Case studies are presented for each type of event. The time it takes to fill/empty the plasma sheet of energetic electrons is quantified based on these events. Extreme events, most of which are associated with enhanced geomagnetic activity, showed that energetic electrons in the plasma sheet can vary up to several orders of magnitude. Interestingly, the energetic electron fluxes inside the plasma sheet can still undergo rapid variations when the solar wind is calm and geomagnetic activity is low.
Published: 18 November 2009
The numerical simulations of the model equation governing the nonlinear dynamics of kinetic Alfvén waves in the intermediate-beta plasmas are performed. When the nonlinearity arises due to the ponderomotive force driven density perturbations of kinetic Alfvén waves, the model equation turns out to be a modified nonlinear Schrödinger equation. This has been solved numerically by using appropriate boundary conditions. The coherent, damped magnetic filaments with turbulent spectra have been observed. Our results reveal the interesting change in spectral index because of the damping effect. The steeper power spectra follow ~k-3.4 scaling. Using the Fokker-Planck equation with the new velocity space diffusion coefficient, we find the distribution function of energetic electrons in these turbulent structures. These turbulent structures can be responsible for plasma heating in Earth's magnetosphere.
Published: 28 October 2009
To investigate the universality of magnetic turbulence in space plasmas, we analyze seven time periods in the free solar wind under different plasma conditions. Three instruments on Cluster spacecraft operating in different frequency ranges give us the possibility to resolve spectra up to 300 Hz. We show that the spectra form a quasiuniversal spectrum following the Kolmogorov's law ~k-5/3 at MHD scales, a ~k-2.8 power law at ion scales, and an exponential ~exp[-sqrt(k rhoe)] at scales k rhoe~[0.1,1], where rhoe is the electron gyroradius. This is the first observation of an exponential magnetic spectrum in space plasmas that may indicate the onset of dissipation. We distinguish for the first time between the role of different spatial kinetic plasma scales and show that the electron Larmor radius plays the role of a dissipation scale in space plasma turbulence.
Published: 15 October 2009
Strong interplanetary shock interactions with the Earth's magnetosphere have great impacts on energetic particle dynamics in the magnetosphere. An interplanetary shock on 7 November 2004 (with the maximum solar wind dynamic pressure of ~70 nPa) was observed by the Cluster constellation to induce significant ULF waves in the plasmasphere boundary, and energetic electrons (up to 2 MeV) were almost simultaneously accelerated when the interplanetary shock impinged upon the magnetosphere. In this paper, the relationship between the energetic electron bursts and the large shock-induced ULF waves is studied. It is shown that the energetic electrons could be accelerated and decelerated by the observed ULF wave electric fields, and the distinct wave number of the poloidal and toroidal waves at different locations also indicates the different energy ranges of electrons resonating with these waves. For comparison, a rather weak interplanetary shock on 30 August 2001 (dynamic pressure ~2.7 nPa) is also investigated. It is found that interplanetary shocks or solar wind pressure pulses with even small dynamic pressure change can have a nonnegligible role in the radiation belt dynamics.
Published: 11 October 2009
The nonlinear kinetic theory is presented for the ion acoustic perturbations at the foot of the Earth's quasiperpendicular bow shock, that is characterized by weakly magnetized electrons and unmagnetized ions. The streaming ions, due to the reflection of the solar wind ions from the shock, provide the free energy source for the linear instability of the acoustic wave. In the fully nonlinear regime, a coherent localized solution is found in the form of a stationary ion hump, which is traveling with the velocity close to the phase velocity of the linear mode. The structure is supported by the nonlinearities coming from the increased population of the resonant beam ions, trapped in the self-consistent potential. As their size in the direction perpendicular to the local magnetic field is somewhat smaller that the electron Larmor radius and much larger that the Debye length, their spatial properties are determined by the effects of the magnetic field on weakly magnetized electrons. These coherent structures provide a theoretical explanation for the bipolar electric pulses, observed upstream of the shock by Polar and Cluster satellite missions.
Published: 06 October 2009
The Earth's magnetosphere is populated by particles originating from the solar wind and the terrestrial ionosphere. A substantial fraction of the plasma from these sources are convected through the magnetotail lobes. In this paper, we present a statistical study of convective plasma transport through the Earth's magnetotail lobes for various geomagnetic conditions. The results are based on a combination of density measurements from the Electric Field and Waves Experiment (EFW) and convection velocities from the Electron Drift Instrument (EDI) on board the Cluster spacecraft. The results show that variations in the plasma flow is primarily attributed to changes in the convection velocity, whereas the plasma density remains fairly constant and shows little correlation with geomagnetic activity. During disturbed conditions there is also an increased abundance of heavier ions, which combined with enhanced convection, cause an accentuation of the mass flow. The convective transport is much slower than the field aligned transport. A substantial amount of plasma therefore escape downtail without ever reaching the central plasma sheet.
Published: 29 September 2009
Some studies over the last decade have indicated that the instability responsible for substorm expansion phase onset may require an external trigger such as a northward turning of the interplanetary magnetic field (IMF). Statistical investigations have lead to contrasting interpretations regarding the relationship between proposed solar wind triggers and substorm onsets identified from geomagnetic data. We therefore present the results of a study into the possible triggering of 260 substorms between 2001-2005, exploiting data from the Cluster and IMAGE satellite missions. We find that only a small fraction (<25%) of the substorms studied are associated with northward turnings of the IMF. However, the majority of the observed onsets are associated with a growth phase characterised using a subset of the criteria employed to define northward-turning IMF triggers. Based upon a case-by-case investigation and the results of an analysis using the statistics of point processes, we conclude that northward-turning structures in the IMF, while sometimes coinciding with the initial phase of individual substorms, are not required to trigger the magnetospheric instability associated with substorm expansion phase onset.
Published: 26 September 2009
Electrostatic solitary waves (ESWs) have been observed in the Earth's magnetosheath region by Cluster. A mechanism for the generation of these structures in terms of electron-acoustic solitons and double layers is discussed. The model simulates the magnetosheath plasma by a four-component plasma system consisting of core electrons, two counterstreaming electron beams, and one type of ions. The analysis is based on the fluid equations and the Poisson equation, and employs the Sagdeev pseudopotential techniques to investigate the solitary waves. The electric field amplitudes, the time durations, and the propagation speeds of the solitary structures predicted by the model are in good agreement with the observed electric fields, pulse widths, and speeds of the electrostatic bipolar pulses.
Published: 25 September 2009
Darrouzet, F., De Keyser, J., Pierrard, V. (Eds.) 2009, IV, 296 pages, 100 illus., 60 in colour, Hardcover. ISBN: 978-1-4419-1322-7 (Print), 978-1-4419-1323-4 (Online) Reprinted from Space Science Reviews journal, Vol. 145/1-2, 2009. This book reviews the state of the art in plasmaspheric science based on the modern observations provided by ESA's Cluster and NASA's IMAGE spacecraft. The plasmasphere, discovered at the beginning of the space age, has remained largely unexplored territory. Now, with innovative observational techniques, new light is being shed on this key region of the magnetosphere. This book sketches the emerging overall picture of a highly structured plasma, sculpted by the ever-changing electromagnetic fields that result from the interaction of the solar wind with the magnetosphere. The Earth's Plasmasphere, written by an international group of scientists representative of the world-wide community, is aimed at researchers and graduate students with an interest in magnetospheric physics, space plasma physics and geophysics. Table of Contents Preface (J. L. Burch & C. P. Escoubet) Foreword (F. Darrouzet, J. De Keyser, & V. Pierrard) CLUSTER and IMAGE: New Ways to Study the Earth's Plasmasphere (J. De Keyser, et al.) Plasmaspheric Density Structures and Dynamics: Properties Observed by the CLUSTER and IMAGE Missions (F. Darrouzet, et al.) Electric Fields and Magnetic Fields in the Plasmasphere: A Perspective from CLUSTER and IMAGE (H. Matsui, et al.) Advances in Plasmaspheric Wave Research with CLUSTER and IMAGE Observations (A. Masson, et al.) Recent Progress in Physics-Based Models of the Plasmasphere (V. Pierrard, et al.) Augmented Empirical Models of Plasmaspheric Density and Electric Field Using IMAGE and CLUSTER Data (B. W. Reinisch, et al.)
Published: 22 August 2009
A higher-order multiscale analysis of the dissipation range of collisionless plasma turbulence is presented using in situ high-frequency magnetic field measurements from the Cluster spacecraft in a stationary interval of fast ambient solar wind. The observations, spanning five decades in temporal scales, show a crossover from multifractal intermittent turbulence in the inertial range to non-Gaussian monoscaling in the dissipation range. This presents a strong observational constraint on theories of dissipation mechanisms in turbulent collisionless plasmas.
Published: 15 August 2009
In the present paper, we first examine some interplanetary directional discontinuities with very small Bn /B (<0.1) using intraspacecraft timing method. It is found that the velocity and magnetic field fluctuations of these directional discontinuities satisfy the Walén relation. We suggest that these directional discontinuities are rotational discontinuities. In addition, we investigate the stability of interplanetary rotational discontinuities using one-dimensional hybrid simulations and found that rotational discontinuities with all values of Bn /B can stably exist in the solar wind. In one simulation run, we find that the rotational discontinuity (RD) is still stable when the ratio, Bn /B, equals 0.0001. Finally, from one-dimensional hybrid simulation, we further find that the ratio is significantly reduced after interaction with interplanetary fast shocks. There are a few mechanisms for generation of RDs. Among them, two mechanisms are well accepted. One is nonlinear evolution of Alfvén waves in the solar wind, and another is magnetic reconnection near the solar surface. For magnetic reconnection, the reconnection rate, V1n /VA1(= Bn /B), in the magnetosphere and solar wind, is usually <0.2. Therefore the generated RDs also have Bn /B < 0.2. On the other hand, the nonlinear evolution of Alfvén waves in the solar wind can generate RDs at all values of Bn /B, which contradicts to the Cluster results. We suggest that interplanetary RDs with small Bn /B are likely been generated through magnetic reconnection.
Published: 12 August 2009
In this article, we study the velocity distribution, density, duration, and energy transport of earthward flow bursts in the inner plasma sheet (IPS) during three substorm phases using the data of Cluster in 2001 and 2002. The mean peak velocity of earthward flow bursts in recovery phases (390 km/s) is smaller than those in growth and expansion phases (490 and 520 km/s). The super earthward flow bursts (V > 1000 km/s) appear more frequently in the expansion phase. The average ion density of earthward flow bursts in the recovery phase is 0.14 cm-3, much smaller than those in growth and expansion phases (0.28 and 0.21 cm-3), indicating that lobe reconnections most likely occur in the recovery phase. The average durations of earthward flow bursts in recovery phase are 48 s, smaller than those in growth and expansion phases (99 and 103 s), suggesting that the reconnections occurring in recovery phase are rather short-lived. The earthward flow bursts in the expansion phase have largest capability of the transport of energy, about 7 times that in the recovery phase. Thus the earthward flow bursts in the expansion phase can produce largest impact effects to the inner magnetosphere.
Published: 17 July 2009
The number and complexity of systems that control Space Science Missions continues to increase. As a result, it is desirable to improve the efficiency of these systems and, in particular, their performance and their productivity. In this paper, we set out a strategy to achieve this goal. In order to talk about improving the Performance and Productivity of a system we need to discuss the functional architecture of the system. In order to make progress, our strategy is to develop a generic methodology that decomposes the functional architecture of a Space Science Mission System and uses this decomposition to identify areas where improvements can be made. This paper concentrates on the decomposition of one specific component, namely the Plan Management System. The purpose of the Plan Management System is to produce an operation plan that contains the directives that will operate the various nodes, i.e. physical parts, of the system such as the ground stations, the spacecraft, the instruments, or even human beings (when these are following specific instructions). In order to be generic, the decomposition of the Plan Management System must make no assumptions about the purpose and implementation choices that must ultimately be made. In order to describe a functional architecture, it must also make no assumptions about the nature and purpose of the nodes that the system will operate or the nodes on which it will run. In particular, it makes no assumptions as to whether the execution of the Plan Management System components is manual or automated or whether the functions will be executed on the ground or in space. -- Remainder of abstract is truncated --
Published: 02 June 2009
In proceedings of the International Conference 'Future perspectives of space plasma and particle instrumentation and international collaborations', held 1-3 November 2006 in Tokyo, Japan.

Using electron and magnetic field data obtained from the Cluster satellites, we identify the spatial distribution of highly accelerated electron distributions up to 10 keV. They are generally isotropic and form flat-top distributions in the phase space. These distributions are observed in the vicinity of the X line associated with the quadrupole-like magnetic field and energetic ions, throughout the plasma sheet. In some cases, these distributions are quasi-stable, continuously observed for a few minutes with a stable Bz polarity and low current density in the center of the plasma sheet.

Published: 17 June 2009
In proceedings of the International Conference 'Future perspectives of space plasma and particle instrumentation and international collaborations', held 1-3 November 2006 in Tokyo, Japan.

With Cluster observations in the magnetotail, we study the dynamics of plasma sheet thinning and stretching in a typical growth phase event of September 12, 2001. The thinning and stretching proceed in parallel, with transient variations. The pre-onset value is Bz~1.5 nT, J~8 nA/m2. The current density increase is not accompanied with a corresponding number density increase. A large (>5 nT) guide field along the cross-tail current direction was registered. An embedded current sheet structure was detected and, therefore, caution is required if making thickness estimations.

Published: 17 June 2009
28-Mar-2020 21:20 UT

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