Articles | Volume 15, issue 9
Ann. Geophys., 15, 1158–1164, 1997

Special issue: Wind Measurements

Ann. Geophys., 15, 1158–1164, 1997

  30 Sep 1997

30 Sep 1997

Zonal mean and tidal dynamics from space: an empirical examination of aliasing and sampling

J. M. Forbes1, M. Kilpatrick1, D. Fritts1, A. H. Manson2, and R. A. Vincent3 J. M. Forbes et al.
  • 1University of Colorado, Boulder, Colorado, USA
  • 2University of Saskatchewan, Saskatoon, Canada
  • 3University of Adelaide, Adelaide, S. Australia

Abstract. Interpretations of space-based measurements of atmospheric parameters in the mesosphere and thermosphere are complicated by large local-time variations at these altitudes. For this reason, satellite orbits are often preferred which precess through all local times one or more times per season. However, the local-time structure of the atmosphere is inherently non-stationary, which can lead to sampling and aliasing difficulties when attempting to deconvolve the measurements into zonal mean and tidal components. In the present study, hourly radar measurements of mesopause-region winds are used to form a mock data base which can be used to gain insight into implications of the aforementioned problems; the use of actual measurements introduces a realistic element of geophysical temporal variability. Assuming zonal symmetry (i.e., migrating tides superimposed on a zonal mean circulation), the radar measurements are sampled from the satellite perspective for orbital inclinations of 57° and 70°, and compared to the ground or true perspective. These comparisons provide realistic estimates of the errors to be expected when attempting to derive mean and tidal components from space-based measurements. For both diurnal and semidiurnal components, and the quoted satellite inclinations, acceptable errors (3–4m/srms) are obtained for data covering 24h local time (i.e., ascending plus descending nodes); the corresponding errors for single-node data (12h local-time coverage) are of order 8–11m/s, and therefore may not represent reliable estimates of the actual tidal components. There exist certain caveats in connection with the latter conclusion which are discussed.

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