Now showing items 21-40 of 566

    • On the influence of neutral turbulence on ambipolar diffusivities deduced from meteor trail expansion. 

      Hall, Chris (Journal article; Peer reviewed; Tidsskriftartikkel, 2002)
      By measuring fading times of radar echoes from underdense meteor trails, it is possible to deduce the ambipolar diffusivities of the ions responsible for these radar echoes. It could be anticipated that these diffusivities increase monotonically with height akin to neutral viscosity. In practice, this is not always the case. Here, we investigate the capability of neutral turbulence to affect ...
    • The WSO, a world-class observatory for the ultraviolet 

      Solheim, Jan Erik; Barstow, M.A.; Binette, L.; Brosch, N.; Cheng, F-Z.; Dennefeld, M.; Gomez de Castro, A.I.; Haubold, H.; van der Hucht, K.A.; Kappelmann, N.; Martinez, P.; Ribak, E.N.; Moisheev, A.; Pagano, I.; Sahade, J.; Wamsteker, W.; Werner, K.; Becker-Ross, H.; Florek, S.; Shustov, B. (Conference object; Konferansebidrag, 2002-09-17)
      The World Space Observatory is an unconventional space project proceeding via distributed studies. The present design, verified for feasibilty, consists of a 1.7-meter telescope operating at the second Largangian point of the Earth-Sun system. The focal plane instruments consist of three UV spectrometers covering the spectral band from Lyman alpha to the atmospheric cutoff with R~55,000 and offering ...
    • WSO/UV: World Space Observatory/Ultraviolet 

      Solheim, Jan Erik; Hernanza, M.; González-Riestra, R.; Wamsteker, W.; Shustov, B.; Barstow, M.; Brosch, N.; Fu-Zhen, C.; Dennefeld, M.; Dopita, M.; Gómez de Castro, A.I.; Kappelmannc, N.l.; Pagano, I.; Sahade, J.; Haubold, H.; Solheim, J.-E.; Martínezc, P. (Journal article; Tidsskriftartikkel, 2002-11-05)
      We summarize the capabilities of the World Space Observatory (UV) Project (WSO/UV). An example of the importance of this project (with a planned launch date of 2007/8) for the study of Novae is given.
    • The Everchanging Pulsating White Dwarf GD358 

      Kepler, S.O.; Solheim, Jan Erik; Nather, R. Edward; Gonzalez Perez, Jose M.; Johannessen, Frank; Winget, Don E.; Nitta, Atsuko; Kleinman, S. J.; Metcalfe, Travis; Sekiguchi, Kazuhiro; Xiaojun, Jiang; Sullivan, Denis; Sullivan, Tiri; Janulis, Rimvydas; Meistas, Edmund; Kalytis, Romualdas; Krzesinski, Jurek; Ogloza, Waldemar; O’Donoghue, Darragh; Romero-Colmenero, Encarni; Martinez, Peter; Dreizler, Stefan; Deetjen, Jochen; Nagel, Thorsten; Schuh, Sonja L.; Vauclair, Gerard; Ning, Fu Jian; Chevreton, Michel; Kanaan, Antonio; Costa, Jos´e Eduardo; Costa, Alex Fabiano Murillo; Wood, Matt A.; Silvestri, Nicole; Ahrens, T.J.; Jones, Aaron Kyle; Collins, Ansley E.; Boyer, Martha; Mukadam, Anjum; Klumpe, Eric W.; Larrison, Jesse; Kawaler, Steve; Riddle, Reed; Ulla, Ana; Bradley, Paul (Journal article; Tidsskriftartikkel; Peer reviewed, 2003-01-23)
      We report 323 hours of nearly uninterrupted time series photometric observations of the DBV star GD 358 acquired with the Whole Earth Telescope (WET) during May 23rd to June 8th, 2000. We acquired more than 232 000 independent measurements. We also report on 48 hours of time-series photometric observations in Aug 1996. We detected the non-radial g-modes consistent with degree ℓ = 1 and radial ...
    • Mesopause dynamics from the scandinavian triangle of radars within the PSMOS-DATAR Project. 

      Hall, Chris; Manson, A.H.; Meek, C.E.; Nozawa, S.; Mitchell, N.J.; Pancheva, D.; Singer, W.; Hoffmann, P. (Journal article; Peer reviewed; Tidsskriftartikkel, 2004-01-01)
      The "Scandinavian Triangle" is a unique trio of radars within the DATAR Project (Dynamics and Temperatures from the Arctic MLT (60–97km) region): Andenes MF radar (69°N, 16°E); Tromsø MF radar (70°N, 19°E) and Esrange "Meteor" radar (68°N, 21°E). The radar-spacings range from 125-270km, making it unique for studies of wind variability associated with small-scale waves, comparisons of large-scale ...
    • Interferometric radar observations of filamented structures due to plasma instabilities and their relation to dynamic auroral rays. 

      Grydeland, Tom; Hagfors, T.; Trondsen, T.S.; Blixt, Erik Mårten; Løvhaug, Unni Pia; La Hoz, Cesar (Journal article; Peer reviewed; Tidsskriftartikkel, 2004-04-02)
      Several explanations have been proposed for Naturally Enhanced ion-acoustic Echoes observed at midand high-latitude Incoherent Scatter observatories. A decisive measure for distinguishing between these explanations is whether or not simultaneously observed up- and downshifted enhancement occur simultaneously, or if they are the result of temporal and/or spatial averaging. The EISCAT Svalbard ...
    • Studies of DC biasing of internal ring on plasma rotation and transport in a toroidal geometry 

      Riccardi, Claudia; Fredriksen, Åshild; Magni, Simone (Conference object; Konferansebidrag, 2004-10)
      We report results from experiments performed to study how a DC bias with respect to the plasma potential is affecting the plasma states in the toroidal geometry of the Blaamann device in Tromso. In the experiments discussed here, a ring with smaller diameter than the limiter was centered inside the bulk of the plasma and its bias varied with respect to the plasma potential. In the electron ...
    • Monthly mean climatology of the prevailing winds and tides in the Arctic mesosphere/lower thermosphere. 

      Hall, Chris; Portnyagin, Y.I.; Solovjova, T.V.; Makarov, N.A.; Merzlyakov, E.G.; Manson, A.H.; Meek, C.E.; Hocking, W.; Pancheva, D.; Hoffmann, P.; Singer, W.; Murayama, Y.; Igarashi, K.; Forbes, J.M.; Palo, S.; Nozawa, S.; Mitchell, N. (Journal article; Peer reviewed; Tidsskriftartikkel, 2004-11-03)
      The Arctic MLT wind regime parameters measured at the ground-based network of MF and meteor radar stations (Andenes 69° N, Tromsø 70° N, Esrange 68° N, Dixon 73.5° N, Poker Flat 65° N and Resolute Bay 75° N) are discussed and compared with those observed in the mid-latitudes. The network of the ground-based MF and meteor radars for measuring winds in the Arctic upper mesosphere and lower thermosphere ...
    • Self-similar transport processes in a two-dimensional realization of multiscale magnetic field turbulence 

      Chiaravalloti, Francesco; Milovanov, Alexander V.; Zimbardo, Gaetano (Journal article; Tidsskriftartikkel; Peer reviewed, 2004-12-14)
      We present the results of a numerical investigation of charged-particle transport across a synthesized magnetic configuration composed of a constant homogeneous background field and a multiscale perturbation component simulating an effect of turbulence on the microscopic particle dynamics. Our main goal is to analyze the dispersion of ideal test particles faced to diverse conditions in the turbulent ...
    • Velocity distribution of Gold nanoparticles trapped on an optical waveguide 

      Hole, JP; Grujic, Katarina; Wilkinson, JS; Hellesø, Olav Gaute (Journal article; Tidsskriftartikkel; Peer reviewed, 2005)
    • Sorting of polystyrene microspheres using a Y-branched optical waveguide 

      Grujic, Katarina; Hole, JP; Wilkinson, JS; Hellesø, Olav Gaute (Journal article; Tidsskriftartikkel; Peer reviewed, 2005)
    • An imaging interferometry capability for the EISCAT Svalbard Radar. 

      Chau, J.L.; Grydeland, Tom; La Hoz, C.; Brekke, Asgeir (Journal article; Peer reviewed; Tidsskriftartikkel, 2005-01-31)
      Interferometric imaging (aperture synthesis imaging) is a technique used by radio astronomers to achieve angular resolution that far surpasses what is possible with a single large aperture. A similar technique has been used for radar imaging studies of equatorial ionospheric phenomena at the Jicamarca Radio Observatory. We present plans for adding an interferometric imaging capability to the ...
    • An interferometer experiment to explore the aspect angle dependence of stimulated electromagnetic emission spectra. 

      Isham, B.; Rietveld, Michael T.; Belyey, Vasyl; Hagfors, T.; Khudukon, B.; La Hoz, Cesar; Brekke, Asgeir; Yurik, R.Yu; Tereshchenko, E.D.; Grill, M.; Heinselman, C. (Journal article; Peer reviewed; Tidsskriftartikkel, 2005-01-31)
      When the Earth's ionosphere is irradiated by a radiofrequency (RF) electromagnetic wave of sufficiently high power density and tuned to match a natural E- or F-region plasma frequency, ionospheric magnetoionic wave modes may be excited and may generate RF electromagnetic sideband waves via nonlinear interactions. These secondary emissions, which may then escape from the ionosphere, have been termed ...
    • A procedure to correct the effects of a relative delay between the quadrature components of radar signals at base band. 

      Westman, A.; Grydeland, Tom; Belyey, Vasyl; La Hoz, Cesar (Journal article; Peer reviewed; Tidsskriftartikkel, 2005-01-31)
      The real and imaginary parts of baseband signals are obtained from a real narrow–band signal by quadrature mixing, i.e. by mixing with cosine and sine signals at the narrow band’s selected center frequency. We address the consequences of a delay between the outputs of the quadrature mixer, which arise when digital samples of the quadrature baseband signals are not synchronised, i.e. when ...
    • Software Radar signal processing. 

      Lind, F.D.; Grydeland, Tom; Holt, J.M.; Erickson, P.J. (Journal article; Peer reviewed; Tidsskriftartikkel, 2005-01-31)
      Software infrastructure is a growing part of modern radio science systems. As part of developing a generic infrastructure for implementing Software Radar systems, we have developed a set of reusable signal processing components. These components are generic softwarebased implementations for use on general purpose computing systems. The components allow for the implementation of signal processing ...
    • Dynamic rayed aurora and enhanced ion-acoustic radar echoes 

      Ivchenko, N.; Blixt, Erik Mårten; Grydeland, Tom; Hagfors, T.; Trondsen, T.S.; La Hoz, Cesar; Lanchester, B.S.; Løvhaug, Unni Pia (Journal article; Peer reviewed; Tidsskriftartikkel, 2005-01-31)
      The generation mechanism for naturally enhanced ion-acoustic echoes is still debated. One important issue is how these enhancements are related to auroral activity. All events of enhanced ion-acoustic echoes observed simultaneously with the EISCAT Svalbard Radar (ESR) and with high-resolution narrow field-of-view auroral imagers have been collected and studied. Characteristic of all the ...
    • The red-sky enigma over Svalbard in December 2002 

      Sigernes, F.; Shumilov, N.; Lloyd, N.; Havnes, O.; Lorentzen, D.A.; Neuber, R.; Hoppe, Ulf-Peter; Degenstein, D.; Moen, J.; Gjessing, Y.; Skartveit, A.; Raustein, E.; Ørbæk, J.B.; Deehr, C.S. (Journal article; Peer reviewed; Tidsskriftartikkel, 2005-07-27)
      On 6 December 2002, during winter darkness, an extraordinary event occurred in the sky, as viewed from Longyearbyen (78° N, 15° E), Svalbard, Norway. At 07:30 UT the southeast sky was surprisingly lit up in a deep red colour. The light increased in intensity and spread out across the sky, and at 10:00 UT the illumination was observed to reach the zenith. The event died out at about 12:30 UT. Spectral ...
    • Relative drift between black aurora and the ionospheric plasma. 

      Kosch, M.J.; Blixt, Erik Mårten; Semeter, J. (Journal article; Tidsskriftartikkel, 2005-07-27)
      Black auroras are recognized as spatially well-defined regions within uniform diffuse aurora where the optical emission is significantly reduced. Although a well studied phenomenon, there is no generally accepted theory for black auroras. One theory suggests that black regions are formed when energetic magnetospheric electrons no longer have access to the loss cone. If this blocking mechanism drifts ...
    • The electron energy distribution during HF pumping, a picture painted with all colors. 

      Gustavsson, B.; Rietveld, Michael T.; Grydeland, Tom; Sergienko, T.; Kosch, M.J.; La Hoz, Cesar; Brändström, B.U.E.; Leyser, T.B.; Isham, B.; Gallop, P.; Aso, T.; Ejiri, M.; Steen, A.; Kaila, K.; Jussila, J.; Holma, H. (Journal article; Peer reviewed; Tidsskriftartikkel, 2005-07-28)
      The shape of the electron energy distribution has long been a central question in the field of highfrequency radio-induced optical emission experiments. This report presents estimates of the electron energy distribution function, fe(E), from 0 to 60 eV, based on optical multiwavelength (6300, 5577, 8446, 4278 A° ) data and 930-MHz incoherent scatter radar measurements of ion temperature, electron ...
    • Solar Wind from Coronal Funnels and Transition Region Lyalpha 

      Esser, Ruth; Lie-Svendsen, Øystein; Janse, Åse Marit; Killie, Mari Anne (Journal article; Tidsskriftartikkel; Peer reviewed, 2005-08-10)
      Using a newly developed gyrotropic solar wind model that extends continuously from the mid-chromosphere to 1 AU and that accounts for radiative losses in the transition region, we have studied the difference between the fast solar wind emanating from a funnel geometry and a ``traditional'' rapidly expanding wind. The main aim is to determine whether or not observations of the Lyalpha intensity in ...