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  • 1
    Electronic Resource
    Electronic Resource
    Vertical velocities associated with gravity waves measured in the mesosphere and lower thermosphere with the EISCAT VHF radar (1998)
    Springer
    Annales geophysicae 16 (1998), S. 1367-1379 
    Details
    ISSN: 0992-7689
    Keywords: Meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The EISCAT VHF radar (69.4°N, 19.1°E) has been used to record vertical winds at mesopause heights on a total of 31 days between June 1990 and January 1993. The data reveal a motion field dominated by quasi-monochromatic gravity waves with representative apparent periods of ∼30–40 min, amplitudes of up to ∼2.5 m s−1 and large vertical wavelength. In some instances waves appear to be ducted. Vertical profiles of the vertical-velocity variance display a variety of forms, with little indication of systematic wave growth with height. Daily mean variance profiles evaluated for consecutive days of recording show that the general shape of the variance profiles persists over several days. The mean variance evaluated over a 10 km height range has values from 1.2 m2s−2 to 6.5 m2s−2 and suggests a semi-annual seasonal cycle with equinoctial minima and solsticial maxima. The mean vertical wavenumber spectrum evaluated at heights up to 86 km has a slope (spectral index) of -1.36 ± 0.2, consistent with observations at lower heights but disagreeing with the predictions of a number of saturation theories advanced to explain gravity-wave spectra. The spectral slopes evaluated for individual days have a range of values, and steeper slopes are observed in summer than in winter. The spectra also appear to be generally steeper on days with lower mean vertical-velocity variance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-998-1367-0
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    The 16-day planetary wave in the mesosphere and lower thermosphere (1999)
    Springer
    Annales geophysicae 17 (1999), S. 1447-1456 
    Details
    ISSN: 0992-7689
    Keywords: Meteorology and atmospheric dynamics ; (middle atmosphere dynamics; thermospheric dynamics; waves and tides)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A meteor radar located at Sheffield in the UK has been used to measure wind oscillations with periods in the range 10–28 days in the mesosphere/lower-thermosphere region at 53.5°N, 3.9°W from January 1990 to August 1994. The data reveal a motion field in which wave activity occurs over a range of frequencies and in episodes generally lasting for less than two months. A seasonal cycle is apparent in which the largest observed amplitudes are as high as 14 ms−1 and are observed from January to mid-April. A minimum in activity occurs in late June to early July. A second, smaller, maximum follows in late summer/autumn where amplitudes reach up to 7–10 ms−1. Considerable interannual variability is apparent but wave activity is observed in the summers of all the years examined, albeit at very small amplitudes near mid summer. This behaviour suggests that the equatorial winds in the mesopause region do not completely prevent inter-hemispheric ducting of the wave from the winter hemisphere, or that it is generated in situ.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-999-1447-9
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Observations of gravity waves in the upper and lower stratosphere by lidar and ozonesondes (1996)
    Springer
    Annales geophysicae 14 (1996), S. 309-314 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Lidar observations of Rayleigh backscatter and temperature profiles measured by ozonesondes have been used to investigate gravity waves in the upper and lower stratosphere, respectively, over Aberystwyth (52.4°N, 4.1°W). Both data sets have been used to investigate the vertical wavenumber spectrum of the wave field at high wavenumbers. Similar analytic techniques applied to each data set enable direct comparison of the spectra. The possibility of laminar structures generated by differential advection contaminating gravity-wave fields deduced from temperature and/or density measurement is discussed and the behaviour of the wave-field mean potential energy reveals a seasonal cycle throughout the stratosphere with a late winter maximum and a summer minimum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-996-0309-y
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    A comparative study of winds and tidal variability in the mesosphere/lower-thermosphere region over Bulgaria and the UK (2000)
    Springer
    Annales geophysicae 18 (2000), S. 1304-1315 
    Details
    ISSN: 0992-7689
    Keywords: Meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Meteor radars located in Bulgaria and the UK have been used to simultaneously measure winds in the mesosphere/lower-thermosphere region near 42.5°N, 26.6°E and 54.5°N, 3.9°W, respectively, over the period January 1991 to June 1992. The data have been used to investigate planetary waves and diurnal and semidiurnal tidal variability over the two sites. The tidal amplitudes at each site exhibit fluctuations as large as 300% on time scales from a few days to the intra-seasonal, with most of the variability being at intra-seasonal scales. Spectral and cross-wavelet analysis reveals closely related tidal variability over the two sites, indicating that the variability occurs on spatial scales large compared to the spacing between the two radars. In some, but not all, cases, periodic variability of tidal amplitudes is associated with simultaneously present planetary waves of similar period, suggesting the variability is a consequence of non-linear interaction. Calculation of the zonal wave number of a number of large amplitude planetary waves suggests that during summer 1991 the 2-day wave had a zonal wave number of 3, but that during January/February 1991 it had a zonal wave number of 4.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-000-1304-3
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    Paper (German National Licenses)
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