Lunar tides in the Mesosphere over Ascension Island (8° S, 14.4° W)

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.