| 1. |
- Dahlgren, Hanna, 1980-, et al.
(författare)
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Relation of anomalous F region radar echoes in the high-latitude ionosphere to auroral precipitation
- 2017
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Ingår i: Annales Geophysicae. - : Copernicus Publications. - 0992-7689 .- 1432-0576. ; 35:3, s. 475-479
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Tidskriftsartikel (refereegranskat)abstract
- Non-thermal echoes in incoherent scatter radar observations are occasionally seen in the high-latitude ionosphere. Such anomalous echoes are a manifestation of plasma instabilities on spatial scales matching the radar wavelength. Here we investigate the occurrence of a class of spatially localized anomalous echoes with an enhanced zero Doppler frequency feature and their relation to auroral particle precipitation. The ionization profile of the E region is used to parametrize the precipitation, with nmE and hmE being the E region peak electron density and the altitude of the peak, respectively. We find the occurrence rate of the echoes to generally increase with nmE and decrease with hmE, thereby indicating a correlation between the echoes and high-energy flux precipitation of particles with a high characteristic energy. The highest occurrence rate of > 20 % is found for hmE = 109 km and nmE = 1011. 9 m−3, averaged over the radar observation volume.
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| 2. |
- Giono, G., et al.
(författare)
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Characterisation of the analogue read-out chain for the CCDs onboard the mesospheric airglow/aerosol tomography and spectroscopy (MATS)
- 2018
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9781510619494 ; 10698
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Konferensbidrag (refereegranskat)abstract
- The MATS satellite aims at observing airglow and noctilucent clouds in the mesosphere. The main instrument consists of a six channels limb imager in the near-ultraviolet and near-infrared. A high signal-to-noise ratio is required for detecting these mesospheric phenomena: 100 and 500 for ultraviolet and infrared, respectively. This is achieved by an optical design minimizing stray-light, but also with a dedicated design of the read-out analogue chain for the CCD on each channel. The requirements and expected light level on the imaging channels are brie y discussed before focusing on the CCD read-out analogue chain, for which the design and performances are presented.
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| 3. |
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| 4. |
- Hamrin, M, et al.
(författare)
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Inhomogeneous transverse electric fields and wave generation in the auroral region: A statistical study
- 2001
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Ingår i: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS. - : AMER GEOPHYSICAL UNION. - 0148-0227. ; 106:A6, s. 10803-10816
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Tidskriftsartikel (refereegranskat)abstract
- We use data from the Freja satellite to investigate the importance of localized transverse DC electric fields for the generation of broadband waves responsible for ion heating in the auroral region. Theoretical models indicate that shear in the plasma Row
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| 5. |
- Ivchenko, N, et al.
(författare)
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Disturbance of plasma environment in the vicinity of the Astrid-2 microsatellite
- 2001
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Ingår i: ANNALES GEOPHYSICAE. - : EUROPEAN GEOPHYSICAL SOCIETY. - 0992-7689. ; 19:6, s. 655-666
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Tidskriftsartikel (refereegranskat)abstract
- The presence of a satellite disturbs the ambient plasma. The charging of the spacecraft creates a sheath around it, and the motion of the satellite creates a wake disturbance. This modification of the plasma environment introduces difficulties in measurin
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| 6. |
- Jiroušek, Martin, et al.
(författare)
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Classification of European bog vegetation of the Oxycocco‐Sphagnetea class
- 2022
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Ingår i: Applied Vegetation Science. - : Wiley. - 1402-2001 .- 1654-109X. ; 25:1, s. 1-19
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Tidskriftsartikel (refereegranskat)abstract
- Aims: Classification of European bog vegetation (Oxycocco- Sphagnetea class); iden -tification of diagnostic species for the class and vegetation subgroups (orders and alliances); development of an expert system for automatic classification of vegetation plots; and production of distribution maps of the Oxycocco- Sphagnetea class and its alliances.Location: Europe.Methods: A data set of vegetation- plot records was compiled to include various bog types over most of the European continent. An unsupervised classification (beta- flexible linkage method, Sørensen distance measure) and detrended correspondenceanalysis (DCA) ordination were applied. Formal definitions of syntaxa based on spe -cies presence and covers, and respecting the results of the unsupervised classifica-tion, were developed and included in a classification expert system.Results: The Oxycocco- Sphagnetea class, its two orders (Sphagno- Ericetalia tetralicisand Sphagnetalia medii) and seven compositionally distinct alliances were formally de -fined. In addition to the syntaxa included in EuroVegChecklist, three new alliances were distinguished: Rubo chamaemori- Dicranion elongati (subarctic polygon and palsa mires); Erico mackaianae- Sphagnion papillosi (blanket bogs of the northwestern IberianPeninsula); and Sphagno baltici- Trichophorion cespitosi (boreal bog lawns). The latter alliance is newly described in this article.Conclusions: This first pan- European formalized classification of European bog veg -etation partially followed the system presented in EuroVegChecklist, but suggested three additional alliances. One covers palsa and polygon mires, one covers Iberian bogs with endemics and one fills the syntaxonomical gap for lawn microhabitats in boreal bogs. A classification expert system has been developed, which allows assign -ment of vegetation plots to the types described.
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| 7. |
- Khotyaintsev, Y, et al.
(författare)
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Electron Energization by Alfvén Waves: Freja and Sounding Rocket Observations
- 2000
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Ingår i: Physica Scripta. - 0281-1847. ; T84, s. 151-
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Tidskriftsartikel (refereegranskat)abstract
- An alternative form of the nonrelativistic permittivity tensor for a homogeneous magnetized plasma in thermal equilibrium is derived in the linear approximation. The derivation follows the lines of Trubnikov's derivation of the relativistic permittivity t
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| 8. |
- Mager, P. N., et al.
(författare)
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On the equatorward phase propagation of high-m ULF pulsations observed by radars
- 2009
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Ingår i: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826 .- 1879-1824. ; 71:16, s. 1677-1680
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Tidskriftsartikel (refereegranskat)abstract
- An often observed and still unexplained feature of the high-m Alfven waves in the terrestrial magnetosphere is their equatorward phase motion, in contrast with low-m waves. We suggest an explanation of this fact in terms of a model of wave excitation by an azimuthally drifting particle inhomogeneity injected during substorm activity. The azimuthal direction of the phase velocity coincides with that of the cloud. If the drift velocity increases with the radial coordinate, the particle cloud is stretched into spiral in the equatorial plane which leads to a radial component of the phase velocity directed toward Earth, that is, an equatorward phase propagation.
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| 9. |
- Marklund, G.T., Ivchenko, N., Karlsson, T., Fazakerley, A., Dunlop, M., Lindqvist, P.A., Buchert, S., Owen, C., Taylor, M., Vaivalds, A., Carter, P., Andre, M. and Balogh, A.
(författare)
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Temporal evolution of the electric field accelerating electrons away from the auroral ionosphere.
- 2001
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Ingår i: Nature. ; 414:6865, s. 724-727
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Tidskriftsartikel (refereegranskat)abstract
- The bright night-time aurorae that are visible to the unaided eye are caused by electrons accelerated towards Earth by an upward-pointing electric field(1-3). On adjacent geomagnetic field lines the reverse process occurs: a downward-pointing electric fie
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| 10. |
- Roth, Lorenz, et al.
(författare)
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Constraints on an exosphere at Ceres from Hubble Space Telescope observations
- 2016
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Ingår i: Geophysical Research Letters. - : Blackwell Publishing. - 0094-8276 .- 1944-8007. ; 43:6, s. 2465-2472
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Tidskriftsartikel (refereegranskat)abstract
- We report far ultraviolet observations of Ceres obtained with the Cosmic Origin Spectrograph (COS) of the Hubble Space Telescope in the search for atomic emissions from an exosphere. The derived brightnesses at the oxygen lines at 1304 Å and 1356 Å are consistent with zero signals within the 1σ propagated statistical uncertainties. The OI 1304 Å brightness of 0.12 ± 0.20 Rayleighs can be explained by solar resonant scattering from an atomic oxygen column density of (8.2 ± 13.4) × 1010 cm-2. Assuming that O is produced by photodissociation of H2O, we derive an upper limit for H2O abundance and compare it to previous observations. Our upper limit is well above the expected O brightness for a tenuous sublimated H2O exosphere, but it suggests that H2O production with a rate higher than 4 × 1026 molecules s-1 was not present at the time of the COS observation. Additionally, we derive an extremely low geometric albedo of ∼1% in the 1300 Å to 1400 Å range.
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