Blar i utgivelsesdato Artikler, rapporter og annet (fysikk og teknologi)

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    • Frequencies of wave packets of whistler-mode chorus inside its source region : a case study 

      Santolik, O.; Kozelov, Boris V; Macusova, E.; Titova, E. E.; Gurnett, D.; Pickett, J. S.; Trakhtengerts, V. Y.; Demekhov, A. G. (Journal article; Tidsskriftartikkel; Peer reviewed, 2008)

    • A study of fine structure of diffuse aurora with ALIS-FAST measurements 

      Gustavsson, Björn Johan; Sergienko, T; Sandahl, Ingrid; Andersson, Laila; Brändström, B. U. E.; Steen, Å (Journal article; Tidsskriftartikkel; Peer reviewed, 2008)
      We present results of an investigation of the fine structure of the night sector diffuse auroral zone, observed simultaneously with optical instruments (ALIS) from the ground and the FAST electron spectrometer from space 16 February 1997. Both the optical and particle data show that the diffuse auroral zone consisted of two regions. The equatorward part of the diffuse aurora was occupied by a pattern ...

    • Estimation of atmospheric temperature and humidity profiles from MODIS data and radiosond data using artificial neural network 

      Akbari, Vahid; Amini, Jalal; Saradjian, Mohammad Reza; Motagh, Mahdi (Journal article; Tidsskriftartikkel; Peer reviewed, 2008)
      The aim of this study is to test the quality of the neural network for retrieving the temperature and humidity by comparison with the radiosond values and a linear regression method. Remote sensed images give useful information about the atmosphere. In this article, MODIS data is used to retrieve temperature and humidity profiles of the atmosphere. Two methods of linear regression and artificial ...

    • The pulsation modes of the pre-white dwarf PG 1159-035 

      Costa, J. E. S.; Solheim, Jan Erik; Kepler, S. O.; Winget, D. E.; O’Brien, M. S.; Kawaler, S. D.; Costa, A. F. M.; Giovannini, O.; Kanaan, A.; Mukadam, A. S.; Mullally, F.; Nitta, A.; Provenc, J. L.; Shipman, H.; Wood, M. A.; Ahrens, T. J.; Grauer, A.; Kilic, M.; Bradley, P. A.; Sekiguchi, K.; Crowe, R.; Jiang, X. J.; Sullivan, D.; Sullivan, T.; Rosen, R.; Clemens, J. C.; Janulis, R.; O’Donoghue, D.; Ogloza, W.; Baran, A.; Silvotti, R.; Marinoni, S.; Vauclair, G.; Dolez, N.; Chevreton, M.; Dreizler, S.; Schuh, S.; Deetjen, J.; Nagel, T.; Gonzalez Perez, J. M.; Ulla, A.; Barstow, Martin; Burleigh, M.; Good, S.; Metcalfe, T.S.; Kim, S.-L.; Lee, H.; Sergeev, A.; Akan, M.C.; Çakırlı, Ö.; Paparo, M.; Viraghalmy, G.; Ashoka, B. N.; Handler, G.; Hürkal, Özlem; Johannessen, F.; Kleinman, S. J.; Kalytis, R.; Krzesinski, J.; Klumpe, E.; Larrison, J.; Lawrence, T.; Meištas, E.; Martinez, P.; Nather, R. E.; Fu, J.-N.; Pakštienė, E.; Rosen, R.; Romero-Colmenero, E.; Riddle, R.; Seetha, S.; Silvestri, N. M.; Vučković, M.; Warner, B.; Zola, S.; Althaus, L. G.; Córsico, A. H.; Montgomery, M. H. (Journal article; Tidsskriftartikkel; Peer reviewed, 2008)
      Context. PG 1159-035, a pre-white dwarf with Teff ≃ 140 000 K, is the prototype of both two classes: the PG 1159 spectroscopic class and the DOV pulsating class. Previous studies of PG 1159-035 photometric data obtained with the Whole Earth Telescope (WET) showed a rich frequency spectrum allowing the identification of 122 pulsation modes. Analyzing the periods of pulsation, it is possible to ...

    • Multi-instrument observations of a large scale Pc4 pulsation 

      Behlke, Rico; Clausen, L. B. N.; Yeoman, T. K.; Lucek, E. A. (Journal article; Tidsskriftartikkel; Peer reviewed, 2008)

    • Ion-dispersion and rapid electron fluctuations in the cusp : a case study 

      Buchert, Stephan C; Lunde, June; Ogawa, Yasunobu; Hirahara, Masafumi; Seki, Kanako; Ebihara, Yuusuke; Sakanoi, Takeshi; Asamura, Kazushi; Okada, Masaki; Raita, Tero; Häggström, Ingemar (Journal article; Tidsskriftartikkel; Peer reviewed, 2008)

    • Scale-free vortex cascade emerging from random forcing in a strongly coupled system 

      Rypdal, Kristoffer; Ratynskaia, Svetlana; Kozelov, Boris; Klumov, Boris; Knapek, Christina (Working paper; Arbeidsnotat, 2008-03-04)
      The notions of self-organised criticality (SOC) and turbulence are traditionally considered to be applicable to disjoint classes of phenomena. Nevertheless, scale-free burst statistics is a feature shared by turbulent as well as self-organised critical dynamics. It has also been suggested that another shared feature is universal non-gaussian probability density functions (PDFs) of global fluctuations. ...

    • Evidence of low-dimensional chaos in magnetized plasma turbulence 

      Živkovic, Tatjana; Rypdal, Kristoffer (Working paper; Arbeidsnotat, 2008-03-10)
      We analyze probe data obtained from a toroidal magnetized plasma configuration suitable for studies of low-frequency gradient-driven instabilities. These instabilities give rise to field-aligned convection rolls analogous to Rayleigh-Benard cells in neutral fluids, and may theoretically develop similar routes to chaos. When using mean-field dimension analysis, we observe low dimensionality, but ...

    • Generation of the lower-thermospheric vertical wind estimated with the EISCAT KST radar at high latitudes during periods of moderate geomagnetic disturbance 

      Brekke, Asgeir; Oyama, S; Watkins, B. J.; Maeda, S.; Shinagawa, H.; Nozawa, S.; Ogawa, Y.; Lathuillere, C.; Kofman, W. (Journal article; Tidsskriftartikkel; Peer reviewed, 2008-06-11)
      Lower-thermospheric winds at high latitudes during moderately-disturbed geomagnetic conditions were studied using data obtained with the European Incoherent Scatter (EISCAT) Kiruna-Sodankylä-Tromsø (KST) ultrahigh frequency (UHF) radar system on 9–10 September 2004. The antenna-beam configuration was newly designed to minimize the estimated measurement error of the vertical neutralwind speed in the ...

    • Modeling temporal fluctuations in avalanching system 

      Rypdal, Martin; Rypdal, Kristoffer (Working paper; Arbeidsnotat, 2008-07-22)
      We demonstrate how to model the toppling activity in avalanching systems by stochastic differential equations (SDEs). The theory is developed as a generalization of the classical mean field approach to sandpile dynamics by formulating it as a generalization of Itoh’s SDE. This equation contains a fractional Gaussian noise term representing the branching of an avalanche into small active clusters, ...

    • A stochastic theory for temporal fluctuations in self-organized critical systems 

      Rypdal, Martin; Rypdal, Kristoffer (Working paper; Arbeidsnotat, 2008-07-22)
      A stochastic theory for the toppling activity in sandpile models is developed, based on a simple mean-field assumption about the toppling process. The theory describes the process as an anti-persistent Gaussian walk, where the diffusion coefficient is proportional to the activity. It is formulated as a generalization of the Itˆo stochastic differential equation with an anti-persistent fractional ...

    • Remote Oxygen Sensing by Ionospheric Excitation (ROSIE) 

      Kalogerakis, K. S.; Gustavsson, Björn Johan; Slanger, T. G.; Rietveld, Michael T; Kendall, E. A.; Pedersen, T. R.; Kosch, M. J. (Journal article; Tidsskriftartikkel; Peer reviewed, 2009)

    • Mesospheric dust and its secondary effects as observed by the ESPRIT payload 

      Havnes, Ove; Surdal, L. H.; Philbrick, C. R. (Journal article; Tidsskriftartikkel; Peer reviewed, 2009)

    • Particle precipitation during NEIAL events : simultaneous ground based nighttime observations at Svalbard 

      Lunde, June; Løvhaug, Unni Pia; Gustavsson, Björn Johan (Journal article; Tidsskriftartikkel; Peer reviewed, 2009)

    • First simultaneous measurements of waves generated at the bow shock in the solar wind, the magnetosphere and on the ground 

      Clausen, L. B. N.; Behlke, Rico; Yeoman, T. K.; Fear, R. C.; Lucek, E. A.; Engebretson, M. J. (Journal article; Tidsskriftartikkel; Peer reviewed, 2009)

    • A novel code for numerical 3-D MHD studies of CME expansion 

      Kleimann, Jens; Kopp, A.; Fichtner, H.; Grauer, R. (Journal article; Tidsskriftartikkel; Peer reviewed, 2009)

    • F-region electron heating by X-mode radiowaves in underdense conditions 

      Gustavsson, Björn Johan; Löfås, H.; Ivchenko, N.; Rietveld, Michael T; Leyser, T. B. (Journal article; Tidsskriftartikkel; Peer reviewed, 2009)

    • Longitudinal development of a substorm brightening arc 

      Aslaksen, Torsten; Shiokawa, K.; Ieda, A.; Nakajima, A.; Sakaguchi, K.; Nomura, R.; Greffen, M.; Spanswick, E.; Donovan, E.; Mende, S. B.; McFadden, J.; Glassmeier, K. H.; Angelopoulos, V.; Miyashita, Y. (Journal article; Tidsskriftartikkel; Peer reviewed, 2009)

    • Phenomena induced by powerful HF pumping towards magnetic zenith with a frequency near the F-region critical frequency and the third electron gyro harmonic frequency 

      Brekke, Asgeir; Blagoveshchenskaya, N. F.; Carlson, H. C.; Kornienko, V. A.; Borisova, T. D.; Rietveld, M. T.; Yeoman, T. K. (Journal article; Tidsskriftartikkel; Peer reviewed, 2009-01-08)
      Multi-instrument observational data from an experiment on 13 October 2006 at the EISCAT/HEATING facility at Tromsø, Norway are analysed. The experiment was carried out in the evening hours when the electron density in the F-region dropped, and the HF pump frequency fH was near and then above the critical frequency of the F2 layer. The distinctive feature of this experiment is that the pump frequency ...

    • On the relationship between auroral absorption, electrojet currents and plasma convection 

      Hansen, Truls Lynne; Kellerman, A. C.; Makarevich, R. A.; Honary, F. (Journal article; Tidsskriftartikkel; Peer reviewed, 2009-02-02)
      In this study, the relationship between auroral absorption, electrojet currents, and ionospheric plasma convection velocity is investigated using a series of new methods where temporal correlations are calculated and analysed for different events and MLT sectors. We employ cosmic noise absorption (CNA) observations obtained by the Imaging Riometer for Ionospheric Studies (IRIS) system in ...