Blar i forfatter "Nozawa, S."

Viser treff 1-8 av 8

    • 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 ...

    • Isolated lower mesospheric echoes seen by medium frequency radar at 70º N, 19º E 

      Hall, Chris; Manson, A.H.; Meek, C.E.; Nozawa, S. (Journal article; Peer reviewed; Tidsskriftartikkel, 2006-11-23)
      We have noted sporadic instances of strong isolated reflections of medium frequency (MF) radar waves from the mesosphere from as low as 50 km altitude and have devised a set of criteria for isolating these apparently anomalous echoes from those normally occurring from progressive partial reflections in the D-region. The object of this study is to map the occurrences of such echoes facilitating ...

    • 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 ...

    • 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 ...

    • On the temporal evolution of turbopause altitude, 1996-2021, 70 N, 19 E 

      Hall, Chris; Nozawa, S. (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-06-04)
      Medium frequency radars with multiple receivers are able to track the movement of the interference pattern on the ground from echoes from irregularities in refractive index. In particular, refractive index in the mesosphere is determined by electron density – commonly known as the ionospheric D-region. Thus using this technique it is possible to determine winds in the height regime 70-90 km, ...

    • Periodicities in energy dissipation rates in the auroral mesosphere/lower thermosphere 

      Nozawa, S.; Hall, Chris; Meek, C.E.; Manson, A.H.; Luo, Yi (Journal article; Peer reviewed; Tidsskriftartikkel, 2003)
      It is possible for medium-frequency (MF) radar systems to estimate kinetic energy dissipation rates by measuring signal fading times. Here, we present approximately 5 years of such results from Tromsø (69° N, 19° E) and in particular, investigate the periodicities present at different altitudes in the regime 80 to 100 km. We detect the known annual variation in the mesosphere and the semiannual ...

    • Testing the hypothesis of the influence of neutral turbulence on the deduction of ambipolar diffusivities from meteor trail expansion 

      Hall, Chris; Aso, T.; Tsutsumi, M.; Nozawa, S.; Manson, A.H.; Meek, C.E. (Journal article; Peer reviewed; Tidsskriftartikkel, 2005-03-30)
      Fading times of radar echoes from underdense meteor trails in the upper mesosphere/lower thermosphere are commonly used to determine ambipolar diffusivities and hence ambient temperature. Diffusivities are generally expected to increase exponentially with height through the region from which the meteor trail echoes are obtained, viz., typically 70-110km altitude for a ~30-MHz radar. In practice, ...

    • Tidal signatures in mesospheric turbulence 

      Nozawa, S.; Hall, Chris; Manson, A.H.; Meek, C.E. (Journal article; Peer reviewed; Tidsskriftartikkel, 2006)
      We search for the presence of tidal signatures in high latitude mesospheric turbulence as parameterized by turbulent energy dissipation rate estimated using a medium frequency radar, quantifying our findings with the aid of correlation analyses. A diurnal periodicity is not particularly evident during the winter and spring months but is a striking feature of the summer mesopause. While semidiurnal ...