Double Star TC-1 Research Articles

Collisionless Plasma Processes at Magnetospheric Boundaries: Role of Strong Nonlinear Wave Interactions

The sunward Poynting flux throughout the magnetosheath and foreshock (directly measured by INERBALL-1, CLUSTER-4, and DOUBLE STAR TC1) and its correlation and bi-correlation with the dynamic pressure of the solar plasma flow have been analyzed. It has been demonstrated for the first time that perturbations caused by resonances in the magnetospheric boundary layers propagate upstream towards the bow shock as the short impulses of the sunward Poynting flux, which excite the strongest three-wave resonances. They are initiated in the foreshock and regulate the bow shock surface oscillations. Another interaction zone near the magnetopause assists plasma flow extra deflection and acceleration around the magnetopause. At the outer boundary of stagnant cusp the turbulent barrier can separate the flowing and stagnant plasmas namely by the three-wave cascades. Therefore, both experiment and magnetohydrodynamic simulation demonstrate the leading role of the discovered waves and nonlinear processes in the collisionless interaction of the plasma flow and magnetic barrier.

БЕССТОЛКНОВИТЕЛЬНОЕ ВЗАИМОДЕЙСТВИЕ В ПЛАЗМЕ: КАК МАГНИТОПАУЗА ВЗАИМОДЕЙСТВУЕТ С УДАРНОЙ ВОЛНОЙ?

Our analysis of a sunward Poynting flux throughout magnetosheath and foreshock (directly measured byINTERBALL-1, CLUSTER-4 and DOUBLE STAR TC1), for the first time clearly demonstrates, how the resonances in the magnetospheric boundary layers are transmitted back wards the bow shock: the short pulses of the sunward Poynting flux initiate the strongest (>80%!) 3-wave interactions with the incident dynamic pressure. They start in the foreshock, regulate the bow shock position and oscillations, and then another near- magnetopause 3-wave strong interactions assist plasma flow extra deflections and acceleration downstream the magnetopause.

Global Model of Plasmaspheric Hiss From Multiple Satellite Observations

AbstractWe present a global model of plasmaspheric hiss, using data from eight satellites, extending the coverage and improving the statistics of existing models. We use geomagnetic activity dependent templates to separate plasmaspheric hiss from chorus. In the region 22–14 magnetic local time (MLT) the boundary between plasmaspheric hiss and chorus moves to lower values with increasing geomagnetic activity. The average wave intensity of plasmaspheric hiss is largest on the dayside and increases with increasing geomagnetic activity from midnight through dawn to dusk. Plasmaspheric hiss is most intense and spatially extended in the 200 to 500 Hz frequency band during active conditions, 400 750 nT, with an average intensity of 1,128 pT in the region 05–17 MLT from 1.5 . In the prenoon sector, waves in the 100 to 200 Hz frequency band peak near the magnetic equator and decrease in intensity with increasing magnetic latitude, inconsistent with a source from chorus outside the plasmapause, but more consistent with local amplification by substorm‐injected electrons. At higher frequencies the average wave intensities in this sector exhibit two peaks, one near the magnetic equator and one at high latitudes, 45° °, with a minimum at intermediate latitudes, 30° °, consistent with a source from chorus outside the plasmapause. In the premidnight sector, the intensity of plasmaspheric hiss in the frequency range 50 < f < 1,000 Hz decreases with increasing geomagnetic activity. The source of this weak premidnight plasmaspheric hiss is likely to be chorus at larger in the postnoon sector that enters that plasmasphere in the postnoon sector and subsequently propagates eastward in MLT.

Quasi-continuous reconnection accompanied by FTEs during IMF Bz ≈ 0 nT observed by Double Star TC-1 at the dawnside magnetopause

During a one-hour interval of interplanetary magnetic field (IMF) Bz≈0nT, the equatorial spacecraft Double Star TC-1 encountered the dawn flank magnetopause many times at the magnetic local time (MLT) of about 08:00 and the latitude of about −27°. During each encounter, reconnection jets were observed with their velocities up to more than 500km/s, significantly higher than the background flow in the magnetosheath. The fast flows match the theoretical prediction of Alfvénic acceleration well. The medium temperature and density of ions in the boundary layer indicate the open magnetic field topology inside this layer. The mainly southward and tailward flows of the plasma jets alongside with the negative slopes of the Walén test indicate that the spacecraft was located south of the reconnection site, consistent with both anti-parallel and component reconnection models. The accelerated flows were observed lasting for about one hour, with some modulations by the oscillations of the magnetopause, but no reversals in the direction of Vz were found during the interval. The significantly enhanced flows in the boundary layer compared to the adjacent magnetosheath indicate that the reconnection was quasi-continuously active at the magnetopause northward of the spacecraft under such IMF conditions. At the same time, the bipolar signatures in BN with enhancements of the magnetic field indicate the occurrence of the Flux Transfer Events (FTEs). The observed reconnection was quasi-continuous, whereas the simultaneously accompanied FTEs were time-dependent under the IMF Bz≈0nT. For this event, however, it is not possible to identify whether the reconnection was anti-parallel or component because the TC-1 was far away from the reconnection site.

Statistical study of chorus wave distributions in the inner magnetosphere using Ae and solar wind parameters

AbstractEnergetic electrons within the Earth's radiation belts represent a serious hazard to geostationary satellites. The interactions of electrons with chorus waves play an important role in both the acceleration and loss of radiation belt electrons. The common approach is to present model wave distributions in the inner magnetosphere under different values of geomagnetic activity as expressed by the geomagnetic indices. However, it has been shown that only around 50% of geomagnetic storms increase flux of relativistic electrons at geostationary orbit while 20% causes a decrease and the remaining 30% has relatively no effect. This emphasizes the importance of including solar wind parameters such as bulk velocity (V), density (n), flow pressure (P), and the vertical interplanetary magnetic field component (Bz) that are known to be predominately effective in the control of high energy fluxes at the geostationary orbit. Therefore, in the present study the set of parameters of the wave distributions is expanded to include the solar wind parameters in addition to the geomagnetic activity. The present study examines almost 4 years (1 January 2004 to 29 September 2007) of Spatio‐Temporal Analysis of Field Fluctuation data from Double Star TC1 combined with geomagnetic indices and solar wind parameters from OMNI database in order to present a comprehensive model of wave magnetic field intensities for the chorus waves as a function of magnetic local time, L shell (L), magnetic latitude (λm), geomagnetic activity, and solar wind parameters. Generally, the results indicate that the intensity of chorus emission is not only dependent upon geomagnetic activity but also dependent on solar wind parameters with velocity and southward interplanetary magnetic field Bs (Bz < 0), evidently the most influential solar wind parameters. The largest peak chorus intensities in the order of 50 pT are observed during active conditions, high solar wind velocities, low solar wind densities, high pressures, and high Bs. The average chorus intensities are more extensive and stronger for lower band chorus than the corresponding upper band chorus.

MHD and kinetic analysis of flow bursts in the Earth’s plasma sheet

In an attempt to study the flow bursts in the Earth’s plasma sheet we select an event that took place on August 7, 2004 in the expansion phase of a substorm, using data from the geomagnetic index, solar wind data, plasma and magnetic field observations from C1 Cluster satellite (the Cluster mission has 4 satellites) and from Double Star TC-1 satellite. In MHD approach, TC-1 firstly observed the tailward flow, then the earthward, and finally the flow alternated in two directions. C1 firstly observed the earthward plasma flow, and then the tailward plasma flow. Before flow bursts are observed by TC-1 and C1, there are disturbances in local entropy with their tailward local entropy larger than those of the earthward. The kinetic features of the plasma flow observed by C1 are similar to those in MHD. However, kinetic characteristics of the plasma flow observed by TC-1 are far more than the description in MHD. The inadequacy mainly exists in two cases: (i) the firstly enhanced tailward flows given in MHD are found without significant increase of the energetic tailward flux; (ii) the almost stagnant flow in MHD is composed of the enhanced energetic ion flux in both earthward and tailward directions. The earthward flow burst observed by TC-1 might be multiple overshoots and rebounds. The earthward flow burst observed by C1 might be simply rebounded in the near-Earth. The pulsation observed by C1 is earlier than that observed by TC-1 with the former intensity less than that of the latter. After the energetic ion flux in the tailward direction is significantly enhanced, the power spectrum intensity of the ULF wave commences to increase obviously, which may suggest that the stream instability is closely correlated with ULF pulsations.

SuperDARN CUTLASS Finland radar observations of high-latitude magnetic reconnections under northward interplanetary magnetic field (IMF) conditions

A number of backscatter power enhancement events with “equatorward-moving radar auroral forms” in the high-latitude ionosphere were observed by SuperDARN CUTLASS Finland radar when the IMF was northward during 09:00–10:00 UT on 26 March 2004. These events were also associated with sunward flow enhancements at each location in the Northern Hemisphere which were shown in ionospheric convections measured by the SuperDARN radars. These are typical features of high-latitude (lobe) magnetic reconnections. The durations of the velocity enhancements imply that the evolution time of the lobe reconnections is about 8–16 min from their origin at the reconnection site to their addition to the magnetotail lobe again. In additional, the Double Star TC-1 spacecraft was moving from magnetosheath into magnetosphere, and crossing the magnetopause near the subsolar region during this interval, and observed typical low-latitude magnetic reconnection signatures. This infers that the dayside high- and low-latitude reconnections may occur simultaneously.

Multi-spacecraft observations of earthward flow bursts

On the basis of the plasma, electric and magnetic fields jointly observed by Cluster and the Double Star TC-1 spacecraft in the Earth’s magnetotail, we have investigated the earthward flow bursts by introducing the momentum equation in the X-direction in the ideal conditions of magneto hydrodynamics (MHD). One earthward flow burst with a peak in excess of 500 km/s was selected, when the four spacecraft of Cluster were located around −16 RE and TC-1 was located around −10 RE in the X-direction. The inter-spacecraft distances in Y and Z directions were smaller than the statistical spatial scales of the bursty bulk flows. When the Y components of E and −V×B were compared, there was no clear breakdown of the frozen-in condition during the earthward flow burst. With the measured plasma and magnetic parameters from two spacecraft at different positions in the magnetotail, the X component of the pressure gradient was calculated. Magnetic tension was calculated using the magnetic field measured at four points, which could be compared with the assumed constant in the past research with single satellite. When the pressure gradient and the magnetic tension were put into the MHD momentum equation, some samples of the earthward flow bursts were accelerated and some were decelerated. The braking process of the earthward flow burst was more complicated than what the past results had shown. The accelerated samples accounted for about one third of the whole earthward flow bursts and discontinuously located among the decelerated elements. The original single earthward flow burst event might be split into several short flow bursts when it was moving to the Earth. Our results may partly illustrate that the duration of fast flows during three phases of substorm becomes short near the Earth. The results are consistent with the past results that fast flows intrude to places earthward the typical braking region.

Coordinated Cluster/Double Star and ground-based observations of dayside reconnection signatures on 11 February 2004

Abstract. A number of flux transfer events (FTEs) were observed between 09:00 and 12:00 UT on 11 February 2004, during southward and dawnward IMF, while the Cluster spacecraft array moved outbound through the northern, high-altitude cusp and dayside high-latitude boundary layer, and the Double Star TC-1 spacecraft was crossing the dayside low-latitude magnetopause into the magnetosheath south of the ecliptic plane. The Cluster array grazed the equatorial cusp boundary, observing reconnection-like mixing of magnetosheath and magnetospheric plasma populations. In an adjacent interval, TC-1 sampled a series of sometimes none standard FTEs, but also with mixed magnetosheath and magnetospheric plasma populations, near the magnetopause crossing and later showed additional (possibly turbulent) activity not characteristic of FTEs when it was situated deeper in the magnetosheath. The motion of these FTEs are analyzed in some detail to compare to simultaneous, poleward-moving plasma concentration enhancements recorded by EISCAT Svalbard Radar (ESR) and "poleward-moving radar auroral forms" (PMRAFs) on the CUTLASS Finland and Kerguelen Super Dual Auroral Radar Network (SuperDARN) radar measurements. Conjugate SuperDARN observations show a predominantly two-cell convection pattern in the Northern and Southern Hemispheres. The results are consistent with the expected motion of reconnected magnetic flux tubes, arising from a predominantly sub-solar reconnection site. Here, we are able to track north and south in closely adjacent intervals as well as to map to the corresponding ionospheric footprints of the implied flux tubes and demonstrate these are temporally correlated with clear ionospheric velocity enhancements, having northward (southward) and eastward (westward) convected flow components in the Northern (Southern) Hemisphere. The durations of these enhancements might imply that the evolution time of the FTEs is about 18–22 min from their origin on magnetopause (at reconnection site) to their addition to the magnetotail lobe. However, the ionospheric response time in the Northern Hemisphere is about 2–4 min longer than the response time in the Southern Hemisphere.

Locations of boundaries of outer and inner radiation belts as observed by Cluster and Double Star

Cluster CIS ion spectrograms measured during the period of the recent solar minimum between April 2007 and June 2009, when Cluster was deep in the radiation belts with its perigee as close as L = 2, are analyzed. The analysis is complemented by Double Star TC-1 satellite data from HIA ion spectrograms on perigee passes during the period of May 15, 2007 to September 28, 2007. We demonstrate how the background counts produced by energetic particles of the radiation belts in Cluster CIS and Double Star HIA instruments can be interpreted to obtain the locations of the boundaries of the outer and inner belts. The obtained L-MLT distribution of boundaries reflects the general structure of the radiation belts. Closer examination of the time-dependent L locations of the boundaries reveals several dips to lower L-shells (from L = 6 to L = 4) in the outer boundary location. The importance of the solar wind pressure increases for the Earthward shift of the outer boundary of the outer belt is discussed. The location and thickness of the slot region are studied using the determined inner boundaries of the outer belt and the outer boundaries of the inner belt. It was found that during intervals of low activity in the solar wind parameters, the slot region widens, which is consistent with weaker inward radial diffusion, and also with weaker local acceleration that can occur only at higher L-shells outside the plasmasphere. We conclude that boundaries of radiation belts determined from background measurements on the instruments with energy ranges that do not cover the radiation belts' energies provide valuable additional information that is useful for radiation belts' model development and validation.

Conjunction of anti-parallel and component reconnection at the dayside MP: Cluster and Double Star coordinated observation on 6 April 2004

Previous theoretical and simulation studies have suggested that the anti-parallel and component reconnection can occur simultaneously on the dayside magnetopause. Certain observations have also been reported to support global conjunct pattern of magnetic reconnection. Here, we show direct evidence for the conjunction of anti-parallel and component MR using coordinated observations of Double Star TC-1 and Cluster under the same IMF condition on 6 April, 2004. The global MR X-line configuration constructed is in good agreement with the S-shape model. Citation: Wang, J., Z. Y. Pu, S. Y. Fu, X. G. Wang, C. J. Xiao, M. W. Dunlop, Y. Wei, Y. V. Bogdanova, Q. G. Zong, and L. Xie (2011), Conjunction of anti-parallel and component reconnection at the dayside MP: Cluster and Double Star coordinated observation on 6 April 2004, Geophys. Res. Lett., 38, L10105, doi:10.1029/2011GL047125.

TC-1 observations of a flux rope: Generation by multiple X line reconnection

[1] On 29 December 2004 the Double Star TC-1 satellite most probably stays close to a reconnection line for about 20 min. The direction of the X line can be evaluated according to the component merging model. During the time of observations, TC-1 also detects a flux transfer event (FTE). It is found that the FTE axis is parallel to such an X line. This observation is more in favor of the single X line and the multiple X lines FTE models, rather than the original Russell and Elphic model. Moreover, particular features of the ion distribution functions and the plasma behavior near the FTE seem to be more consistent with a multiple X line generation mechanism. The period under study is characterized by a large and negative Earth's dipole tilt, and the reconnection line close to TC-1 is found to follow the magnetic equator, passing northward of the subsolar/stagnation point. These facts lead to speculate that the FTE is generated when a secondary X line, probably passing through the subsolar/stagnation point and with approximately the same orientation of the X line near TC-1, is activated southward of TC-1.

The large-scale magnetospheric electric field observed by Double Star TC-1

Abstract. The relationship between the average structure of the inner magnetospheric large-scale electric field and geomagnetic activity levels has been investigated by Double Star TC-1 data for radial distances ρ between 4.5 RE and 12.5 RE and MLT between 18:00 h and 06:00 h from July to October in 2004 and 2005. The sunward component of the electric field decreases monotonically as ρ increases and approaches zero as the distance off the Earth is greater than 10 RE. The dawn-dusk component is always duskward. It decreases at about 6 RE where the ring current is typically observed to be the strongest and shows strong asymmetry with respect to the magnetic local time. Surprisingly, the average electric field obtained from TC-1 for low activity is almost comparable to that observed during moderate activity, which is always duskward at the magnetotail (8 RE~12 RE).

Simultaneous FAST and Double Star TC1 observations of broadband electrons during a storm time substorm

Broadband electrons (BBEs) exhibit remarkable electron flux enhancements over a broad energy range (0.03–30 keV) near the equatorward edge of the auroral oval during geomagnetic storms. Here, we report a BBE event observed by the Fast Auroral Snapshot (FAST) satellite at 1355–1359 UT, ∼61°–66° invariant latitudes, ∼0600 magnetic local time (MLT), and ∼3800 km altitude during a storm on 25 July 2004. The Double Star (DS) TC1 satellite was located near the magnetic equator at L = 5.7, close to the same local time as FAST. We investigate the acceleration process of BBEs from the inner magnetosphere to near the ionosphere by comparing electron data obtained by FAST and DS TC1. We also investigate both plasma and field variations in the inner magnetosphere associated with substorm onset using DS TC1 data to examine the relationship between the BBEs and the storm time substorm. Ground geomagnetic field data show a positive H‐bay at ∼1349 UT at ∼0600 MLT, indicating that a storm time substorm started just before the appearance of the BBEs. At ∼1350 UT, a tailward ion flow was observed by DS TC1. Then, DS TC1 observed a local dipolarization and a drastic ion density enhancement at ∼1351 UT, indicating that particle heating associated with the substorm was occurring in the inner magnetosphere. From ∼1352 UT, electron fluxes were isotropically enhanced at energies above ∼0.5 keV as observed by DS TC1. On the other hand, the pitch angle distribution of BBEs at the FAST altitude showed field‐aligned lower‐energy electrons below ∼0.5 keV and isotropic higher‐energy electrons above ∼0.5 keV. From these data, it was inferred that the BBEs might consist of two energy components due to the acceleration or heating of electrons at different altitudes in association with the storm time substorm.

Interplanetary shock transmitted into the Earth's magnetosheath: Cluster and Double Star observations

Abstract. On day 7 May 2005, the plasma instruments on board Double Star TC1 and Cluster SC3 spacecraft register inside the magnetosheath, at 19:15:12 and 19:16:20 UT, respectively, a strong pressure pulse due to the impact of an interplanetary shock wave (IS) on the terrestrial bow shock. The analysis of this event provides clear and quantitative evidences confirming and strengthening some results given by past simulations and observational studies. In fact, here we show that the transmitted shock is slowed down with respect to the incident IS (in the Earth's reference frame) and that, besides the transmitted shock, the IS – bow shock interaction generates a second discontinuity. Moreover, supported also by a special set three-dimensional magnetohydrodynamic simulation, we discuss, as further effects of the interaction of the IS with the magnetosphere, other two interesting aspects of the present event, that is: the TC1 double crossing of the bow shock (observed few minutes after the impact of the IS) and the presence, only in the SC3 data, of a third discontinuity produced inside the magnetosheath.

Mirror waves and mode transition observed in the magnetosheath by Double Star TC-1

Abstract. The Double Star TC-1 magnetosheath pass on 26 February 2004 is used to investigate magnetic field fluctuations. Strong compressional signatures which last for more than an hour have been found near the magnetopause behind a quasi-perpendicular bow shock. These compressional structures are most likely mirror mode waves. There is a clear wave transition in the magnetosheath which probably results from the change of the interplanetary magnetic field (IMF) cone angle. The wave characteristics in the magnetosheath are strongly controlled by the type of the upstream bow shock.

Deformation and evolution of solar wind discontinuities through their interactions with the Earth's bow shock

The present study examines the interaction of solar wind discontinuities with the Earth's bow shock, using multipoint observations in the magnetosheath by Time History of Events and Macroscale Interactions During Substorms (THEMIS), Cluster, and Double Star TC1. We focus on the deformation and evolution of two discontinuities observed on 21 June 2007, one of which involves a density increase and a magnetic field decrease, while the other is accompanied by a density decrease and a magnetic field increase. In the magnetosheath, the discontinuities are deformed into a concave shape; that is, the normal is inclined toward dusk (dawn) on the dawnside (duskside). The density‐increase (‐decrease) discontinuity is being compressed (expanded) as it propagates in the magnetosheath. We conclude that the compression (expansion) is due to antisunward (sunward) motion of the bow shock which is initiated or enhanced by the impact of the discontinuity on the bow shock. The steepening of Bz reversal followed by an overshoot of the total magnetic field, which appears at the trailing edge of the density‐decrease discontinuity, is also discussed.

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.

Low-frequency fluctuations in the magnetosheath: Double Star TC-1 and Cluster observations

The magnetic field variations are analyzed in the range of time periods from 4 s to 240 s in the magnetosheath observed by the Double Star TC-1 and Cluster in 2004. The characteristics of the magnetic field fluctuations are strongly controlled by the angle between the upstream interplanetary magnetic field (IMF) and the normal of the bow shock. Generally speaking, the magnetic field fluctuations in the quasi-parallel magnetosheath are more intense than those in the quasi-perpendicular ones. Almost purely compressional waves are found in the quasi-perpendicular magnetosheath. With the increase of the local plasma β, both the magnitude and direction of the magnetic field fluctuate more intensely. There exists an inverse correlation between the local temperature anisotropy T⊥/T∥ and the plasma β.

Ultra low frequency waves observed by Double Star TC-1 in the plasmasphere boundary layer

The characteristic and properties of ULF waves in the plasmasphere boundary layer during two very quiet periods are present. The ULF waves were detected by Double Star TC-1 when the spacecraft passed through the plasmasphere in an outbound and inbound trajectories, respectively. A clear association between the ULF waves and periodic variations of energetic ions fluxes was observed. The observations showed that the wave frequency was higher inside the plasmasphere than outside. The mechanism generating these ULF waves and possible diagnosing of the “classical plasmapause” location with the ULF wave were discussed.