| 1. |
- Giang, Tony, et al.
(författare)
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Outflowing protons and heavy ions as a source for the sub-keV ringcurrent
- 2009
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Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 27:2, s. 839-849
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Tidskriftsartikel (refereegranskat)abstract
- Data from the Cluster CIS instrument have been used for studying proton and heavy ion (O+ and He+ ) char- acteristics of the sub-keV ring current. Thirteen events with dispersed heavy ions (O+ and He+ ) were identified out of two years (2001 and 2002) of Cluster data. Allevents took place during rather geomagnetically quiet periods. Three of those events have been investigated in detail: 21 August 2001, 26 November 2001 and 20 February 2002. These events were chosen from varying magnetic local times (MLT), and they showed different characteristics. In this article, we discuss the potential source for sub-keV ring current ions. We show that: (1) outflows of terrestrialsub-keV ions are supplied to the ring current also during quiet geomagnetic conditions; (2) the composition of the out-flow implies an origin that covers an altitude interval from the low-altitude ionosphere to the plasmasphere, and (3) terrestrial ions are moving upward along magnetic field lines, at times forming narrow collimated beams, but frequently also as broad beams. Over time, the ion beams are expected to gradually become isotropised as a result of wave-particleinteraction, eventually taking the form of isotropic drifting sub-keV ion signatures. We argue that the sub-keV energy-time dispersed signatures originate from field-aligned terrestrial ion energising and outflow, which may occur at all local times and persist also during quiet times.
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| 2. |
- Hayakawa, Hisashi, et al.
(författare)
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The extreme space weather event in 1903 october/november : An outburst from the quiet sun
- 2020
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 897:1
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Tidskriftsartikel (refereegranskat)abstract
- While the Sun is generally more eruptive during its maximum and declining phases, observational evidence shows certain cases of powerful solar eruptions during the quiet phase of solar activity. Occurring in the weak Solar Cycle 14 just after its minimum, the extreme space weather event in 1903 October-November is one of these cases. Here, we reconstruct the time series of geomagnetic activity based on contemporary observational records. With the mid-latitude magnetograms, the 1903 magnetic storm is thought to be caused by a fast coronal mass ejection (≈1500 km s-1) and is regarded as a superstorm with an estimated minimum of the equivalent disturbance storm time index (Dst') of ≈-531 nT. The reconstructed time series has been compared with the equatorward extension of auroral oval (≈44. 1 in invariant latitude) and the time series of telegraphic disturbances. This case study shows that potential threats posed by extreme space weather events exist even during weak solar cycles or near their minima.
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| 3. |
- Kataoka, Ryuho, et al.
(författare)
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Compound auroral micromorphology : ground-based high-speed imaging
- 2015
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Ingår i: EARTH PLANETS AND SPACE. - : Springer Science and Business Media LLC. - 1880-5981. ; 67
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Tidskriftsartikel (refereegranskat)abstract
- Auroral microphysics still remains partly unexplored. Cutting-edge ground-based optical observations using scientific complementary metal-oxide semiconductor (sCMOS) cameras recently enabled us to observe the fine-scale morphology of bright aurora at magnetic zenith for a variety of rapidly varying features for long uninterrupted periods. We report two interesting examples of combinations of fine-scale rapidly varying auroral features as observed by the sCMOS cameras installed at Poker Flat Research Range (PFRR), Alaska, in February 2014. The first example shows that flickering rays and pulsating modulation simultaneously appeared at the middle of a surge in the pre-midnight sector. The second example shows localized flickering aurora associated with growing eddies at the poleward edge of an arc in the midnight sector.
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| 4. |
- Schillings, Audrey, et al.
(författare)
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The fate of O+ ions observed in the plasma mantle: particle tracing modelling and cluster observations
- 2020
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Ingår i: Annales Geophysicae. - : Copernicus Publications. - 0992-7689 .- 1432-0576. ; 38:3, s. 645-656
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Tidskriftsartikel (refereegranskat)abstract
- Ion escape is of particular interest for studying the evolution of the atmosphere on geological timescales. Previously, using Cluster-CODIF data, we investigated the oxygen ion outflow from the plasma mantle for different solar wind conditions and geomagnetic activity. We found significant correlations between solar wind parameters, geomagnetic activity (Kp index), and the O+ outflow. From these studies, we suggested that O+ ions observed in the plasma mantle and cusp have enough energy and velocity to escape the magnetosphere and be lost into the solar wind or in the distant magnetotail. Thus, this study aims to investigate where the ions observed in the plasma mantle end up. In order to answer this question, we numerically calculate the trajectories of O+ ions using a tracing code to further test this assumption and determine the fate of the observed ions. Our code consists of a magnetic field model (Tsyganenko T96) and an ionospheric potential model (Weimer 2001) in which particles initiated in the plasma mantle region are launched and traced forward in time. We analysed 131 observations of plasma mantle events in Cluster data between 2001 and 2007, and for each event 200 O+ particles were launched with an initial thermal and parallel bulk velocity corresponding to the velocities observed by Cluster. After the tracing, we found that 98 % of the particles are lost into the solar wind or in the distant tail. Out of these 98 %, 20 % escape via the dayside magnetosphere.
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