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| Larmor radius size density holes discovered in the solar wind upstream of Earth's bow shock |
| The Cluster and Double Star satellites recently observed plasma density holes upstream of Earth's collisionless bow shock to apogee distances of ~19 and 13 Earth radii, respectively. A survey of 147 isolated density holes using 4 s time resolution data shows they have a mean duration of ~17.9±10.4 s, but holes as short as 4 s are observed. The average fractional density depletion (delta n/n) inside the holes is ~0.68±0.14. The upstream edge of density holes can have enhanced densities that are five or more times the solar wind density. Particle distributions show the steepened edge can behave like a shock. Multispacecraft analyses show the density holes move with the solar wind, can have an ion gyroradius scale, and could be expanding. A small normal electric field points outward. 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 backstreaming particles interacting with the solar wind are important. |
| Publication date: 22 May 2006 |
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| Flux closure during a substorm observed by Cluster, Double Star, IMAGE FUV, SuperDARN, and Greenland magnetometers |
| We examine magnetic flux closure during an extended substorm interval on 29 August 2004 involving a two-stage onset and subsequent re-intensifications. Cluster and Double Star provide observations of magnetotail dynamics, while the corresponding auroral evolution, convection response, and substorm current wedge development are monitored by IMAGE FUV, SuperDARN, and the Greenland magnetometer chain, respectively. The first stage of onset is associated with the reconnection of closed flux in the plasma sheet; this is accompanied by a short-lived auroral intensification, a modest substorm current wedge magnetic bay, but no significant ionospheric convection enhancement. The second stage follows the progression of reconnection to the open field lines of the lobes; accompanied by prolonged auroral bulge and westward-travelling surge development, enhanced magnetic bays and convection. We find that the tail dynamics are highly influenced by ongoing dayside creation of open flux, leading to flux pile-up in the near-tail and a step-wise down-tail motion of the tail reconnection site. In all, 5 dipolarizations are observed, each associated with the closure of ~0.1 GWb of flux. Very simple calculations indicate that the X-line should progress down-tail at a speed of 20 km s-1, or 6 RE between each dipolarization. |
| Publication date: 23 Mar 2006 |
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| Double Star - First Results |
| Editors: C. P. Escoubet, Z.-X. Liu, and Z. Pu
This special issue of Annales Geophysicae presents the mission, the instruments and the first results of the Double Star programme. Double Star is the first mission in collaboration between China and ESA. Double Star has been a great opportunity for the European and Chinese scientists to enhance the knowledge of the Sun-Earth connection. Double Star, together with Cluster, brings six coordinated spacecraft to study small-, medium- and large-scale plasma processes in geospace. This is the first time that European instruments have been flown on a Chinese spacecraft as part of the payload. |
| Publication date: 08 Nov 2005 |
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| Simultaneous Double Star and Cluster FTEs observations on the dawnside flank of the magnetosphere |
| We present Cluster and Double Star-1 (TC-1) observations from a close magnetic conjunction on 8 May 2004. The five spacecraft were on the dawnside flank of the magnetosphere, with TC-1 located near the equatorial plane and Cluster at higher geographic latitudes in the Southern Hemisphere. TC-1, at its apogee, skimmed the magnetopause for almost 8h (between 08:00-16:00 UT). Flux Transfer Events (FTEs), moving southward/tailward from the reconnection site, were observed by TC-1 throughout almost all of the period. Cluster, travelling on a mainly dawn-dusk trajectory, crossed the magnetopause at around 10:30 UT in the same Magnetic Local Time (MLT) sector as TC-1 and remained close to the magnetopause boundary layer in the Southern Hemisphere. The four Cluster spacecraft observed FTEs for a period of 6.5h between 07:30 and 14:00 UT.
The very clear signatures and the finite transverse sizes of the FTEs observed by TC-1 and Cluster imply that, during this event, sporadic reconnection occurred. From the properties of these FTEs, the reconnection site was located northward of both TC-1 and Cluster on the dawn flank of the magnetosphere. Reconnection occurred between draped magnetosheath and closed magnetospheric field lines. Despite variable interplanetary magnetic field (IMF) conditions and IMF-Bz turnings, the IMF clock angle remained greater than 70° and the location site appeared to remain relatively stable in position during the whole period. This result is in agreement with previous studies which reported that the dayside reconnection remained active for an IMF clock angle greater than 70°. The simultaneous observation of FTEs at both Cluster and TC-1, separated by 2h in MLT, implies that the reconnection site on the magnetopause must have been extended over several hours in MLT. |
| Publication date: 08 Nov 2005 |
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| The Gamma-Ray Giant Flare from SGR 1806-20: Evidence of Crustal Cracking via Initial Timescales |
| Soft gamma-ray repeaters (SGRs) are neutron stars that emit short (<~1 s) and energetic (<~1042 erg s-1) bursts of soft gamma-rays. Only four of them are currently known. Occasionally, SGRs have been observed to emit much more energetic "giant flares'' (~1044-1045 erg s-1). These are exceptional and rare events. We report here on serendipitous observations of the intense gamma-ray flare from SGR 1806-20 that occurred on 2004 December 27. Unique data from the Cluster and Double Star TC-2 satellites, designed to study the Earth's magnetosphere, provide the first observational evidence of three separate timescales within the early (first 100 ms) phases of this class of events. These observations reveal that in addition to the initial very steep (<0.25 ms) X-ray onset, there is first a 4.9 ms exponential rise timescale followed by a continued exponential rise in intensity on a timescale of 70 ms. These three timescales are a prominent feature of current theoretical models, including the timescale (several milliseconds) for fracture propagation in the crust of the neutron star. |
| Publication date: 15 Jul 2005 |
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| An overview of the scientific objectives and technical configuration of the NeUtral Atom Detector Unit (NUADU) for the Chinese Double Star Mission |
| The scientific objectives of an advanced NeUtral Atom Detector Unit (NUADU) designed for the Chinese Double Star Polar Mission, which is scheduled for launch in July 2004, are described. The potential during this mission to realize, hitherto unprecedented, integrated studies of global dynamic magnetospheric processes through combining with NUADU data contemporaneous measurements made aboard the CLUSTER II, IMAGE and TWINS spacecraft is also discussed and a short technical account of NUADU provided. |
| Publication date: 15 Jan 2005 |
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| ESA SP-1276: ESA's Report to the 35th COSPAR Meeting |
Scientific editor: A. Gimenez
Editor: A. Wilson
The report for the 35th COSPAR Meeting covers, as in previous issues, the missions
of the Scientific Programme of ESA in the areas of astronomy, Solar System
exploration and fundamental physics. This year's COSPAR Meeting occurs only
weeks after the Saturn-orbit insertion of the Cassini spacecraft - carrying Europe's
Huygens probe to explore the atmosphere of Titan - and at the same time as the
launch of the second satellite of the Double Star project. |
| Publication date: 15 Jun 2004 |
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| ESA SP-1259: ESA's Report to the 34th COSPAR Meeting |
Scientific editor: B. Foing
Editor: A. Wilson
The report to the 34th COSPAR Meeting covers the missions of the Scientific Programme of ESA in the areas of astronomy, Solar System exploration and fundamental physics. |
| Publication date: 01 Oct 2002 |
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