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Ann. Geophys., 25, 9-12, 2007
www.ann-geophys.net/25/9/2007/
© European Geosciences Union 2007
Lunar tides in the Mesosphere over Ascension Island (8° S, 14.4° W)
D. J. Sandford and N. J. Mitchell
Centre for Space, Atmospheric & Oceanic Science, Department of Electronic and Electrical Engineering, University of Bath, Bath, BA2 7AY, UK
Abstract. A meteor radar has been used to measure the horizontal
winds in the equatorial mesosphere and lower thermosphere over Ascension
Island (8.0° S, 14.4° W). A 5-year data set covering the interval 2001–2005
over the height range 78–100 km is considered. The lunar M2
tide is clearly evident in the data and reaches amplitudes as large as
11 ms−1 in the meridional component and 6 ms−1 in the zonal
component. These are the first observations of the lunar tide made over the
equatorial Atlantic sector. Comparisons of the observed seasonal behaviour
with the model of Vial and Forbes (1994) reveals good agreement, but the
observed amplitudes are generally larger and there is a systematic phase
difference of ~2 h with the observed phases lagging the model.
Comparisons with observations made at other equatorial sites suggest the
presence of non-migrating lunar M2 tides and/or significant
inter-annual variability.
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