Double Star Spacecraft Research Articles

Bandwidths and amplitudes of chorus‐like banded emissions measured by the TC‐1 Double Star spacecraft

AbstractCharacteristics of banded whistler‐mode emissions are derived from a database of chorus‐like events obtained from the complete data set of the wave measurements provided by the Spatio‐Temporal Analysis of Field Fluctuation‐Digital Wave Processing (STAFF‐DWP) wave instrument on board the TC‐1 Double Star spacecraft. Our study covers the full operational period of this spacecraft (almost 4 years). Our entire data set has been collected within 30° of geomagnetic latitude at L shells between 2 and 12 and below 4 kHz. All events have been processed automatically to accurately determine their power spectral density (PSD), bandwidth, and amplitude. We found most cases of chorus‐like banded emissions at L≤10 on the dawnside and dayside. The upper band emissions (above one half of the equatorial electron cyclotron frequency) occur almost 20 times less often than the lower band, and their average amplitude is almost 3 times smaller than for the lower band. Intense upper band emissions cover smaller L shell, magnetic local time (MLT), and magnetic latitudes regions than intense lower band emissions. The intense nightside and dawnside chorus‐like banded emissions were observed at low magnetic latitudes, while the intense dayside and duskside emissions were mostly found at higher magnetic latitudes. The amplitudes of dayside lower band waves slightly increase as they propagate away from the geomagnetic equator and are smaller than chorus amplitudes on nightside and dawnside. The PSD, the amplitude of the lower band, its frequency bandwidth, and its occurrence rate significantly increase with increasing geomagnetic activity, while all these parameters for the upper band are not so strongly dependent on the geomagnetic activity.

Single‐event upsets in the Cluster and Double Star Digital Wave Processor instruments

AbstractRadiation‐induced upsets are an important issue for electronic circuits operating in space. Upsets due to solar protons, trapped protons, and galactic cosmic rays are frequently observed. Modeling the expected frequency of upsets is a necessary part of the design process for space hardware. The Cluster and Double Star spacecraft were respectively European and Chinese missions dedicated to the study of the wave and particle environment in the Earth's magnetosphere. All four Cluster spacecraft and one Double Star spacecraft included a Digital Wave Processor (DWP) instrument. The primary purpose of this instrument was as the central controller of the Wave Experiment Consortium. This paper investigates the occurrence of radiation‐induced single‐event upsets in these DWP instruments. The memory devices used in the DWP were not specifically radiation‐hardened parts and so are relatively sensitive to single‐event effects. We present the experience gained during the first 11 years of operation of the Cluster mission and the nearly 4 year lifetime of the Double Star TC‐1 spacecraft and compare with models of the radiation environment.

A study of the changes of the near‐Earth plasma sheet and lobe driven by multiple substorms: Comparison with a full particle simulation of reconnection

Comparisons of multispacecraft observations and full‐particle simulations are used to understand magnetotail changes during substorms and the related cross‐tail current disruptions/reductions. We first show that the electric field accompanying current disruptions can be measured in the tail lobe from the drift velocity of oxygen beams. A stormy period is studied here with a fleet of spacecraft including the four Cluster spacecraft and the Double Star spacecraft TC‐1 in the tail, ACE and Geotail respectively in the solar wind and magnetosheath, and five LANL geostationary satellites, thus allowing the determination of the direction of propagation of the substorm disturbances. Each substorm here corresponds to an energy‐loading period followed by a dipolarization of the magnetic field seen from 11 to 18 RE. Plasma sheet thinning inside 12 RE occurs during energy loading and is enhanced at the onset of strong dissipations of magnetic energy, which precede by several minutes particle injections at 6.6 RE. Dipolarizations coincide with an increase of the lobe electric field, up to several mV/m. This study shows that the onset of the magnetic energy conversion occurs at about ∼10–11 RE and that once initiated, the perturbation propagates both toward the Earth and toward the distant tail. Comparisons of the measurements with recently published 2D full particle simulations of the reconnection process by Oka et al. (2008) indicate a good agreement between data and simulated magnetic lobe signatures. This suggests that the lobe magnetic changes are the signature of a tailward retreating neutral line, with its associated current disruption/reduction.

Observations and simulations of a highly structured plasma sheet during northward IMF

We investigated a highly structured plasma sheet populated by counterstreaming beams observed by the Cluster and Double Star spacecraft on October 10, 2005, during an extended interval of northward interplanetary magnetic field (IMF). We used Wind spacecraft observations as input into our global magnetohydrodynamic (MHD) simulation of the event, and launched ions from the low‐latitude boundary layer, determined to be the source of the observed ions, in our large‐scale kinetic (LSK) particle tracing calculation that used the time‐dependent global fields from the MHD simulation. We found that a highly structured plasma sheet was formed in which the dawn and dusk halves were temporarily decoupled because of the presence of flux ropes in the center of the tail, possibly the result of localized near‐Earth reconnection. Our LSK simulation results showed good agreement with observed spectrograms and velocity distribution functions. On the dawn side, the ions launched in our simulation first formed a plasma sheet boundary layer (PSBL). Subsequent interactions of these ions with the current sheet scattered them and formed the central plasma sheet (CPS). On the dusk side, however, the topology of the magnetotail, including the formation of highly stretched field lines in the dusk flank and of a flux rope on open field lines in the center of the tail resulted in a structured plasma sheet, with counterstreaming beams present throughout the plasma sheet, including its center portion. This is very different from the classical picture of the PSBL in which layered counterstreaming beams exist only at the outer edges of the plasma sheet and do not penetrate the CPS.

Energetic ion dynamics of the inner magnetosphere revealed in coordinated Cluster‐Double Star observations

Since early 2004 the Chinese spacecraft Tan Ce 1 (TC‐1), first component of the Double Star (DSP) mission, has been on an equatorial elliptical orbit (13.4 RE apogee), allowing the study of the dynamics of the Earth's magnetosphere in conjunction with the four European Cluster spacecraft (19.6 RE apogee). The Cluster and Double Star spacecraft orbits are such that the spacecraft are almost in the same meridian, allowing conjugate studies. The four Cluster spacecraft highly eccentric polar orbit at 4 RE perigee permits them to sample the ring current, the radiation belts, and the outer plasmasphere from south to north, almost following the same magnetic flux tube (latitudinal profile), whereas TC‐1, with its very low‐perigee equatorial orbit, gives the plasma profile across L shells. Coordinated ion measurements provided by the Cluster Ion Spectrometry and Hot Ion Analyzer instruments onboard Cluster and TC‐1, respectively, obtained during quiet conditions, disturbed geomagnetic conditions, and an intense storm, are used to analyze crossings of the plasmasphere and the ring current region. Multiple narrow ion energy bands (“nose‐like” structures) are simultaneously observed by both Cluster and TC‐1. These observations reveal the large‐scale character of these structures and pose a challenge for the simulation and modeling of the inner magnetosphere populations.

Magnetosphere response to the 2005 and 2006 extreme solar events as observed by the Cluster and Double Star spacecraft

The four identical Cluster spacecraft, launched in 2000, orbit the Earth in a tetrahedral configuration and on a highly eccentric polar orbit (4–19.6 R E). This allows the crossing of critical layers that develop as a result of the interaction between the solar wind and the Earth’s magnetosphere. Since 2004 the Chinese Double Star TC-1 and TC-2 spacecraft, whose payload comprise also backup models of instruments developed by European scientists for Cluster, provided two additional points of measurement, on a larger scale: the Cluster and Double Star orbits are such that the spacecraft are almost in the same meridian, allowing conjugate studies. The Cluster and Double Star observations during the 2005 and 2006 extreme solar events are presented, showing uncommon plasma parameters values in the near-Earth solar wind and in the magnetosheath. These include solar wind velocities up to ∼900 km s −1 during an ICME shock arrival, accompanied by a sudden increase in the density by a factor of ∼5 and followed by an enrichment in He ++ in the secondary front of the ICME. In the magnetosheath ion density values as high as 130 cm −3 were observed, and the plasma flow velocity there reached values even higher than the typical solar wind velocity. These resulted in unusual dayside magnetosphere compression, detection of penetrating high-energy particles in the magnetotail, and ring current development following several successive injections of energetic particles in the inner magnetosphere, which “washed out” the previously formed nose-like ion structures.

Introduction to special section on Double Star‐Cluster Coordinated Studies on Magnetospheric Dynamic Processes

[1] The Double Star Program (DSP) is not only the first Chinese scientific satellite program but also the first collaborative mission between the China National Space Administration (CNSA) and the European Space Agency (ESA) [Liu et al., 2005]. This mission consists of two spacecraft, designed to investigate magnetospheric, global dynamic processes, and their response to solar wind-forcing and interplanetary magnetic field (IMF) disturbances, in conjunction with the previously launched four-satellite ESA Cluster Mission (Figure 1). The first spacecraft of DSP, called in Chinese ‘‘Tan Ce –1’’ (TC-1–Explorer-1), was launched successfully by a Chinese Long March 2C rocket at 2006 CET on 29 December 2003, into an elliptical orbit with perigee height of 550 km and apogee of 66,970 km, and inclined at 28.5 degrees to the equator (orbital period 27.4 h). TC-2 was launched also by a Chinese Long March 2C rocket at 1515 CET on 25 July 2004 into a polar orbit, having a perigee height of 700 km and apogee height of 39,000 km, with a period of 11.7 h. [2] The orbits of the two Double Star spacecraft have been specially designed to complement the ESA Cluster mission by maximizing the time periods when both Cluster and Double Star are in the same magnetospheric regions or connected magnetically with each other. The two missions together allow simultaneous observations of the Earth magnetosphere from six points in space in a three-dimensional manner. Together with the four Cluster spacecraft, on the dayside, the TC-1 orbit enables prolonged observations of the Earth’s bow shock and simultaneous observations of magnetic reconnection near the subsolar point and near the cusp, as well as on the flanks of the magnetosphere at both high and low latitudes. On the nightside, the combined spacecraft allow Earth’s dynamic magnetotail to be investigated, simultaneously in key regions where magnetospheric substorm onset and particle acceleration are thought to occur. The TC-2 orbit design focused on physical processes taking place over the high-latitude magnetospheric region, the development of auroral substorms, and the intensification of the ring current. [3] Both Double Star satellites are cylindrical in shape with a diameter of 2.1 m, a height of 1.2 m, and a mass of 340 kg (Figure 2). The two Double Star spacecraft structures are identical and only differ in the communication booms. TC-1 carries one communication boom and TC-2 has two booms. In addition, two deployable 3.5 m booms are attached at the bottom of the spacecraft and carry the fluxgate and search coil magnetometers. The spin axis is set to lie perpendicular to the ecliptic and the spacecraft makes 15 rotations per minute (the same as Cluster) enabling the full, three-dimensional particle distribution functions to be measured every 4 s. [4] Each Double Star spacecraft carries eight scientific instruments to measure the magnetic field, waves, electron, ions of low and high energy, and energetic neutral atoms. The highlight aspect of Europe’s participation in Double Star program was to provide seven identical instruments (spares or duplicates) to those flying on the Cluster spacecraft.

Ionospheric oxygen ions dominant bursty bulk flows: Cluster and Double Star observations

Two extreme oxygen‐rich bursty bulk flows (BBFs) with predominant ionospheric O+ ions have been observed on 8 November 2004 by the Cluster and Double Star spacecraft during a strong magnetic storm time period with Dst = −373 nT. The oxygen densities in two BBFs are found to be 3–5 times larger than the hydrogen densities and the oxygen thermal pressures in the BBFs are 8 times higher than the hydrogen thermal pressure. These BBFs are associated with nested magnetic structures and are observed simultaneously by the CLUSTER and the DSP TC‐1 spacecraft. Thus, the flow braking region should be greatly pushed inside the usual pressure balance region (even inside the inner magnetosphere) since the BBF is dominated by oxygen ions. Results in this paper indicate that oxygen dominated BBFs can be formed during a strong magnetic storm time period. The observations made in this paper suggest that singly charged oxygen ions embedded in the BBFs could be carried into the ring current region by bursty flows during very intense magnetic storms.

Observation of three distinct ion populations at the Kelvin-Helmholtz-unstable magnetopause

Abstract. We report Double Star spacecraft observations of the dusk-flank magnetopause and its boundary layer under predominantly northward interplanetary magnetic field (IMF). Under such conditions the flank low-latitude boundary layers (LLBL) of the magnetosphere are known to broaden. The primary candidate processes associated with the transport of solar wind plasma into the LLBL are: (1) local diffusive plasma transport associated with the Kelvin-Helmholtz instability (KHI), (2) local plasma penetration owing to magnetic reconnection in the vicinity of the KHI-driven vortices, and (3) via a pre-existing boundary layer formed through double high-latitude reconnection on the dayside. Previous studies have shown that a cold population of solar wind origin is typically mixed with a hot population of magnetospheric origin in the LLBL. The present observations show the coexistence of three distinct ion populations in the dusk LLBL, during an interval when the magnetopause is unstable to the KHI: (1) a typical hot magnetospheric population, (2) a cold population that shows parallel temperature anisotropy, and (3) a distinct third cold population that shows perpendicular temperature anisotropy. Although no unambiguous conclusion may be drawn from this single event, we discuss the possible mechanisms at work and the origin of each population by envisaging three likely sources: hot magnetospheric plasma sheet, cold magnetosheath of solar wind origin, and cold plasma of ionospheric origin.

Simulation study of magnetic holes at the Earth's collisionless bow shock

Recent observations by the Cluster and Double Star spacecraft at the Earth's bow shock have revealed localized magnetic field and density holes in the solar wind plasma. These structures are characterized by a local depletion of the magnetic field and the plasma density, and by a strong increase of the plasma temperature inside the magnetic and density cavities. Our objective here is to report results of a hybrid-Vlasov simulations of ion-Larmor-radius sized plasma density cavities with parameters that are representative of the high-beta solar wind plasma at the Earth's bow shock. We observe the asymmetric self-steepening and shock-formation of the cavity, and a strong localized temperature increase (by a factor of 5–7) of the plasma due to reflections and shock surfing of the ions against the collisionless shock. Temperature maxima are correlated with density minima, in agreement with Cluster observations. For oblique incidence of the solar wind, we observe efficient acceleration of ions along the magnetic field lines by the shock drift acceleration process.

Modeling PSBL high speed ion beams observed by Cluster and Double Star

On October 8, 2004, the Cluster and Double Star spacecraft crossed the near-Earth (12–19 R E) magnetotail neutral sheet during the recovery phase of a small, isolated substorm. Although they were separated in distance by ∼7 R E and in time by ∼30 min, both Cluster and Double Star observed steady, but highly structured Earthward moving >1000 km/s high speed H + beams in the PSBL. This paper utilizes a global magnetohydrodynamic (MHD) simulation driven by Wind spacecraft solar wind input to model the large-scale structure of the PSBL and large-scale kinetic (LSK) particle tracing calculations to investigate the similarities and differences in the properties of the observed beams. This study finds that the large-scale shape of the PSBL is determined by the MHD configuration. On smaller scales, the LSK calculations, in good qualitative agreement with both Cluster and Double Star observations, demonstrated that the PSBL is highly structured in both time and space, on time intervals of less than 2 min, and spatial distances of the order of 0.2–0.5 R E. This picture of the PSBL is different from the ordered and structured region previously reported in observations.

The Double Star Plasma Electron and Current Experiment

Abstract. The Double Star Project is a collaboration between Chinese and European space agencies, in which two Chinese magnetospheric research spacecraft, carrying Chinese and European instruments, have been launched into equatorial (on 29 December 2003) and polar (on 25 July 2004) orbits designed to enable complementary studies with the Cluster spacecraft. The two Double Star spacecraft TC-1 and TC-2 each carry a Double Star Plasma Electron and Current Experiment (PEACE) instrument. These two instruments were based on Cluster Flight Spare equipment, but differ from Cluster instruments in two important respects. Firstly, a Double Star PEACE instrument has only a single sensor, which must be operated in a manner not originally envisaged in the Cluster context in order to sample the full range of energies. Secondly, the DPU hardware was modified and major changes of onboard software were implemented, most notably a completely different approach to data compression has been adopted for Double Star, which allows high resolution 3-dimensional distributions to be transmitted almost every spin, a significant improvement over Cluster. This paper describes these instruments, and includes examples of data collected in various magnetospheric regions encountered by the spacecraft which have been chosen to illustrate the power of combined Double Star and Cluster measurements.

The Double Star magnetic field investigation: instrument design, performance and highlights of the first year's observations

Abstract. One of the primary objectives of the Double Star mission is the accurate measurement of the magnetic field vector along the orbits of the two spacecraft. The magnetic field is an essential parameter for the understanding of space plasma processes and is also required for the effective interpretation of data from the other instruments on the spacecraft. We present the design of the magnetic field instrument onboard both of the Double Star spacecraft and an overview of the performance as measured first on-ground and then in-orbit. We also report the results of in-flight calibration of the magnetometers, and the processing methods employed to produce the final data products which are provided to Double Star investigators, and the wider community in general. Particular attention is paid to the techniques developed for removing magnetic interference generated by the solar arrays on the first (equatorial orbiting) spacecraft. Results from the first year of operations are reviewed in the context of combined observations by Double Star and Cluster, and examples given from the different regions visited by the spacecraft to date.