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1.
  • Carter, J. A., et al. (author)
  • Ground-based and additional science support for SMILE
  • 2024
  • In: Earth and Planetary Physics. - : Science Press. - 2096-3955. ; 8:1, s. 275-298
  • Journal article (peer-reviewed)abstract
    • The joint European Space Agency and Chinese Academy of Sciences Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) mission will explore global dynamics of the magnetosphere under varying solar wind and interplanetary magnetic field conditions, and simultaneously monitor the auroral response of the Northern Hemisphere ionosphere. Combining these large-scale responses with medium and fine-scale measurements at a variety of cadences by additional ground-based and space-based instruments will enable a much greater scientific impact beyond the original goals of the SMILE mission. Here, we describe current community efforts to prepare for SMILE, and the benefits and context various experiments that have explicitly expressed support for SMILE can offer. A dedicated group of international scientists representing many different experiment types and geographical locations, the Ground-based and Additional Science Working Group, is facilitating these efforts. Preparations include constructing an online SMILE Data Fusion Facility, the discussion of particular or special modes for experiments such as coherent and incoherent scatter radar, and the consideration of particular observing strategies and spacecraft conjunctions. We anticipate growing interest and community engagement with the SMILE mission, and we welcome novel ideas and insights from the solar-terrestrial community.
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3.
  • Lockwood, M, et al. (author)
  • Coordinated Cluster and ground-based instrument observations of transient changes in the magnetopause boundary layer during an interval of predominantly northward IMF : relation to reconnection pulses and FTE signatures
  • 2001
  • In: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 19:10-12, s. 1613-1640
  • Research review (peer-reviewed)abstract
    • We study a series of transient entries into the low-latitude boundary layer (LLBL) of all four Cluster spacecraft during an outbound pass through the mid-afternoon magnetopause ([X(GSM), Y(GSM), Z(GSM)] approximate to [2, 7, 9] R(E)). The events take place during an interval of northward IMF, as seen in the data from the ACE satellite and lagged by a propagation delay of 75 min that is well-defined by two separate studies: (1) the magnetospheric variations prior to the northward turning (Lockwood et al., 2001, this issue) and (2) the field clock angle seen by Cluster after it had emerged into the magnetosheath (Opgenoorth et al., 2001, this issue). With an additional lag of 16.5 min, the transient LLBL events cor-relate well with swings of the IMF clock angle (in GSM) to near 90degrees. Most of this additional lag is explained by ground-based observations, which reveal signatures of transient reconnection in the pre-noon sector that then take 10-15 min to propagate eastward to 15 MLT, where they are observed by Cluster. The eastward phase speed of these signatures agrees very well with the motion deduced by the cross-correlation of the signatures seen on the four Cluster spacecraft. The evidence that these events are reconnection pulses includes: transient erosion of the noon 630 nm (cusp/cleft) aurora to lower latitudes; transient and travelling enhancements of the flow into the polar cap, imaged by the AMIE technique; and poleward-moving events moving into the polar cap, seen by the EISCAT Svalbard Radar (ESR). A pass of the DMSP-F15 satellite reveals that the open field lines near noon have been opened for some time: the more recently opened field lines were found closer to dusk where the flow transient and the poleward-moving event intersected the satellite pass. The events at Cluster have ion and electron characteristics predicted and observed by Lockwood and Hapgood (1998) for a Flux Transfer Event (FTE), with allowance for magnetospheric ion reflection at Alfvenic disturbances in the magnetopause reconnection layer. Like FTEs, the events are about 1 R(E) in their direction of motion and show a rise in the magnetic field strength, but unlike FTEs, in general, they show no pressure excess in their core and hence, no characteristic bipolar signature in the boundary-normal component. However, most of the events were observed when the magnetic field was southward, i.e. on the edge of the interior magnetic cusp, or when the field was parallel to the magnetic equatorial plane. Only when the satellite begins to emerge from the exterior boundary (when the field was northward), do the events start to show a pressure excess in their core and the consequent bipolar signature. We identify the events as the first observations of FTEs at middle altitudes.
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4.
  • Oyama, S., et al. (author)
  • An Ephemeral Red Arc Appeared at 68 degrees MLat at a Pseudo Breakup During Geomagnetically Quiet Conditions
  • 2020
  • In: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 125:10
  • Journal article (peer-reviewed)abstract
    • Various subauroral optical features have been studied by analyzing data collected during periods of geomagnetic disturbances. Most events have been typically found at geomagnetic latitudes of 45-60 degrees. In this study, however, we present a red arc event found at geomagnetic 68 degrees north (L approximate to 7.1) in the Scandinavian sector during a period of geomagnetically quiet conditions within a short intermission between two high-speed solar wind events. The red arc appeared to coincide with a pseudo breakup at geomagnetic 71-72 degrees N and a rapid equatorward expansion of the polar cap. However, the red arc disappeared in approximately 7 min. Simultaneous measurements with the Swarm A/C satellites indicated the appearance of the red arc at the ionospheric trough minimum and a conspicuous enhancement of the electron temperature, suggesting the generation of the arc by heat flux. Since there are meaningful differences in the red arc features from already-known subauroral optical features such as the stable auroral red (SAR) arc, we considered that the red arc is a new phenomenon. We suggest that the ephemeral red arc may represent the moment of SAR arc birth associated with substorm particle injection, which is generally masked by bright dynamic aurorae.
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5.
  • Palin, Laurianne, et al. (author)
  • Modulation of the substorm current wedge by bursty bulk flows : 8 September 2002- Revisited
  • 2016
  • In: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 121:5, s. 4466-4482
  • Journal article (peer-reviewed)abstract
    • The ultimate formation mechanism of the substorm current wedge (SCW) remains to date unclear. In this study, we investigate its relationship to plasma flows at substorm onset and throughout the following expansion phase. We revisit the case of 8 September 2002, which has been defined as one of the best textbook examples of a substorm because of its excellent coverage by both spacecraft in the magnetotail and ground-based observatories. We found that a dense sequence of arrival of nightside flux transfer events (NFTEs; which can be understood as the lobe magnetic signature due to a bursty bulk flow travelling earthward in the central plasma sheet) in the near-Earth tail leads to a modulation (and further step-like builtup) of the SCW intensity during the substorm expansion phase. In addition, we found that small SCWs are created also during the growth phase of the event in association with another less intense sequence of NFTEs. The differences between the sequence of NFTEs in the growth and expansion phase are discussed. We conclude that the envelope of the magnetic disturbances which we typically refer to as an intense magnetic substorm is the result of a group or sequence of more intense and more frequent NFTEs.
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6.
  • Aikio, A. T., et al. (author)
  • Swarm Satellite and EISCAT Radar Observations of a Plasma Flow Channel in the Auroral Oval Near Magnetic Midnight
  • 2018
  • In: Journal of Geophysical Research - Space Physics. - : AMER GEOPHYSICAL UNION. - 2169-9380 .- 2169-9402. ; 123:6, s. 5140-5158
  • Journal article (peer-reviewed)abstract
    • We present Swarm satellite and EISCAT radar observations of electrodynamical parameters in the midnight sector at high latitudes. The most striking feature is a plasma flow channel located equatorward of the polar cap boundary within the dawn convection cell. The flow channel is 1.5 degrees wide in latitude and contains southward electric field of 150 mV/m, corresponding to eastward plasma velocities of 3,300 m/s in the F-region ionosphere. The theoretically computed ion temperature enhancement produced by the observed ion velocity is in accordance with the measured one by the EISCAT radar. The total width of the auroral oval is about 10 degrees in latitude. While the poleward part is electric field dominant with low conductivity and the flow channel, the equatorward part is conductivity dominant with at least five auroral arcs. The main part of the westward electrojet flows in the conductivity dominant part, but it extends to the electric field dominant part. According to Kamide and Kokubun (1996), the whole midnight sector westward electrojet is expected to be conductivity dominant, so the studied event challenges the traditional view. The flow channel is observed after substorm onset. We suggest that the observed flow channel, which is associated with a 13-kV horizontal potential difference, accommodates increased nightside plasma flows during the substorm expansion phase as a result of reconnection in the near-Earth magnetotail.
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8.
  • Berthomier, M., et al. (author)
  • Alfven : magnetosphere-ionosphere connection explorers
  • 2012
  • In: Experimental astronomy. - Dordrecht : Springer. - 0922-6435 .- 1572-9508. ; 33:2-3, s. 445-489
  • Journal article (peer-reviewed)abstract
    • The aurorae are dynamic, luminous displays that grace the night skies of Earth's high latitude regions. The solar wind emanating from the Sun is their ultimate energy source, but the chain of plasma physical processes leading to auroral displays is complex. The special conditions at the interface between the solar wind-driven magnetosphere and the ionospheric environment at the top of Earth's atmosphere play a central role. In this Auroral Acceleration Region (AAR) persistent electric fields directed along the magnetic field accelerate magnetospheric electrons to the high energies needed to excite luminosity when they hit the atmosphere. The "ideal magnetohydrodynamics" description of space plasmas which is useful in much of the magnetosphere cannot be used to understand the AAR. The AAR has been studied by a small number of single spacecraft missions which revealed an environment rich in wave-particle interactions, plasma turbulence, and nonlinear acceleration processes, acting on a variety of spatio-temporal scales. The pioneering 4-spacecraft Cluster magnetospheric research mission is now fortuitously visiting the AAR, but its particle instruments are too slow to allow resolve many of the key plasma physics phenomena. The Alfv,n concept is designed specifically to take the next step in studying the aurora, by making the crucial high-time resolution, multi-scale measurements in the AAR, needed to address the key science questions of auroral plasma physics. The new knowledge that the mission will produce will find application in studies of the Sun, the processes that accelerate the solar wind and that produce aurora on other planets.
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9.
  • Borälv, E., et al. (author)
  • Correlation between ground-based observations of substorm signatures and magnetotail dynamics
  • 2005
  • In: Annales Geophysicae. - 0992-7689 .- 1432-0576. ; 23, s. 997-1011
  • Journal article (peer-reviewed)abstract
    • We present a substorm event study combining Cluster and ground-based instrumentation. For this event ground-based magnetograms show a substorm onset and two separate substorm intensifications over Scandinavia, at the time located in the pre-midnight sector. During the substorm Cluster is located in the southern plasma sheet at a downtail distance of 18.5 Re. For all the substorm signatures seen on ground, corresponding plasma sheet drop-outs and re-entries of all or individual spacecraft of the Cluster constellation are observed. In general, plasma sheet drop-outs are assumed to be due to plasma sheet thinning/thickening and/or to magnetotail flapping. However, in the literature there has been some disagreement on both spatial and temporal characteristics of plasma sheet thinning and thickening during substorms. We therefore investigate the causes for the plasma sheet drop-outs for this event, which at first glance appears to show plasma sheet thinning at substorm onset, contradictory to the present standpoint in the literature.
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11.
  • Janhunen, P, et al. (author)
  • Characteristics of a stable arc based on FAST and MIRACLE observations
  • 2000
  • In: ANNALES GEOPHYSICAE-ATMOSPHERES HYDROSPHERES AND SPACE SCIENCES. - : SPRINGER VERLAG. - 0992-7689. ; 18:2, s. 152-160
  • Journal article (peer-reviewed)abstract
    • A stable evening sector are is studied using observations from the FAST satellite at 1250 km altitude and the MIRACLE ground-based network, which contains all-sky cameras, coherent radars (STARE), and magnetometers. Both FAST and STARE observe a northward
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12.
  • Karlsson, SBP, et al. (author)
  • Solar wind control of magnetospheric energy content: Substorm quenching and multiple onsets
  • 2000
  • In: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS. - : AMER GEOPHYSICAL UNION. - 0148-0227. ; 105:A3, s. 5335-5356
  • Journal article (peer-reviewed)abstract
    • In this paper we report coordinated multispacecraft and ground-based observations of a double substorm onset close to Scandinavia on November 17, 1996. The Wind and the Geotail spacecraft, which were located in the solar wind and the subsolar magnetosheat
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13.
  • KAURISTIE, K, et al. (author)
  • ANALYSIS OF THE SUBSTORM TRIGGER PHASE USING MULTIPLE GROUND-BASED INSTRUMENTATION
  • 1995
  • In: GEOPHYSICAL RESEARCH LETTERS. - : AMER GEOPHYSICAL UNION. - 0094-8276. ; 22:15, s. 2065-2068
  • Journal article (other academic/artistic)abstract
    • During the substorm trigger phase, i.e. during the last few minutes before the onset, the slowly and linearly developing growth phase features strengthen exponentially. Often the enhanced auroral activity fades abruptly during a couple of minutes just pri
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14.
  • Kauristie, K, et al. (author)
  • Auroral precipitation fading before and at substorm onset: ionospheric and geostationary signatures
  • 1997
  • In: ANNALES GEOPHYSICAE-ATMOSPHERES HYDROSPHERES AND SPACE SCIENCES. - : SPRINGER VERLAG. - 0992-7689. ; 15:8, s. 967-983
  • Journal article (other academic/artistic)abstract
    • Rapid fading of auroral activity a few minutes before substorm breakup has earlier been analyzed in case-studies. Here we report on a study in which all-sky camera (ASC) and magnetic data over 3 years were examined to find breakups that were accompanied b
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16.
  • Kauristie, K., et al. (author)
  • On the Usage of Geomagnetic Indices for Data Selection in Internal Field Modelling
  • 2017
  • In: Space Science Reviews. - : SPRINGER. - 0038-6308 .- 1572-9672. ; 206:1-4, s. 61-90
  • Research review (peer-reviewed)abstract
    • We present a review on geomagnetic indices describing global geomagnetic storm activity (Kp, am, Dst and dDst/dt) and on indices designed to characterize high latitude currents and substorms (PC and AE-indices and their variants). The focus in our discussion is in main field modelling, where indices are primarily used in data selection criteria for weak magnetic activity. The publicly available extensive data bases of index values are used to derive joint conditional Probability Distribution Functions (PDFs) for different pairs of indices in order to investigate their mutual consistency in describing quiet conditions. This exercise reveals that Dst and its time derivative yield a similar picture as Kp on quiet conditions as determined with the conditions typically used in internal field modelling. Magnetic quiescence at high latitudes is typically searched with the help of Merging Electric Field (MEF) as derived from solar wind observations. We use in our PDF analysis the PC-index as a proxy for MEF and estimate the magnetic activity level at auroral latitudes with the AL-index. With these boundary conditions we conclude that the quiet time conditions that are typically used in main field modelling (, and ) correspond to weak auroral electrojet activity quite well: Standard size substorms are unlikely to happen, but other types of activations (e.g. pseudo breakups ) can take place, when these criteria prevail. Although AE-indices have been designed to probe electrojet activity only in average conditions and thus their performance is not optimal during weak activity, we note that careful data selection with advanced AE-variants may appear to be the most practical way to lower the elevated RMS-values which still exist in the residuals between modeled and observed values at high latitudes. Recent initiatives to upgrade the AE-indices, either with a better coverage of observing stations and improved baseline corrections (the SuperMAG concept) or with higher accuracy in pinpointing substorm activity (the Midlatitude Positive Bay-index) will most likely be helpful in these efforts.
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17.
  • Kauristie, K, et al. (author)
  • What can we tell about global auroral electrojet activity from a single meridional magnetometer chain?
  • 1996
  • In: ANNALES GEOPHYSICAE-ATMOSPHERES HYDROSPHERES AND SPACE SCIENCES. - : SPRINGER VERLAG. - 0992-7689. ; 14:11, s. 1177-1185
  • Journal article (other academic/artistic)abstract
    • The AE indices are generally used for monitoring the level of magnetic activity in the auroral oval region. In some cases, however, the oval is either so expanded or contracted that the latitudinal coverage of the AE magnetometer chain is not adequate. Th
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  • PELLINEN, RJ, et al. (author)
  • THE TRIGGER PHASE OF MAGNETOSPHERIC SUBSTORMS
  • 1994
  • In: GEOMAGNETIZM I AERONOMIYA. - : MEZHDUNARODNAYA KNIGA. - 0016-7940. ; 34:6, s. 1-8
  • Journal article (other academic/artistic)abstract
    • The last few minutes of the substorm growth phase before the auroral breakup show features distinct both from the gradual growth phase development and from the rapidly evolving expansion phase. During this time the optical auroras fade, energetic particle
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20.
  • Sergeev, V. A., et al. (author)
  • Substorm-Related Near-Earth Reconnection Surge : Combining Telescopic and Microscopic Views
  • 2019
  • In: Geophysical Research Letters. - : Blackwell Publishing. - 0094-8276 .- 1944-8007. ; 46:12, s. 6239-6247
  • Journal article (peer-reviewed)abstract
    • A strong ~11-min-long surge of the lobe reconnection was observed during a substorm on the tailward side of the near-Earth neutral line. In the southern lobe near the reconnection separatrix the MMS spacecraft observed short-duration earthward electron beams providing the local Hall current, tailward propagating Alfven wave (AW) bursts with Poynting flux up to 10−4 W/m2, and large-amplitude E field spikes (e-holes) and low hybrid waves. The reconnection surge was accompanied by substorm current wedge formation and fast poleward expansion of auroral bulge-related westward electrojet in the conjugate ionosphere. During its meridional crossing above the expanding bulge the Metop-2 spacecraft observed an intense energetic precipitation spike near the expected X line foot point and confirmed the dipolarized character of magnetic field lines inside of the bulge. Globally the observed average reconnection rate (<Ey > ~3.3 mV/m) was sufficient to produce the magnetic flux increase in the bulge, associated with observed fast poleward expansion (about 6° latitude in 5 min).
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21.
  • Syrjäsuo, M., Pulkkinen, T.I., Pellinen, R.P., Janhunen, P., Kauristie, K., Viljanen, A., Opgenoorth, H.J., Karllson, P., Wallman, S., Eglitis, P., Nielsen, E. and Thomas, C. (author)
  • Observations of substorm electrodynamics using the miracle network.
  • 2001
  • In: The 4th International Conference on Substorms, ICS4. - : Terra Scient. Publ. Comp. Tokyo, Japan. Kaje Hamana, Japan.
  • Conference paper (other academic/artistic)
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