Intraseasonal variability of high-resolution Doppler imager winds in the equatorial mesosphere and lower thermosphere

Abstract

Analyses of high-resolution Doppler imager (HRDI) daytime equatorial zonal winds indicate significant variability on time scales of 20-121 days. These appear as transient oscillations in the equatorial zonal mean zonal wind between 70 and 100 km. The oscillations are characterized by two maxima near 75 and 95 km that are out of phase, separated by a minimum near 80 km. These features move downward in time and exhibit equatorial symmetry with maximum values at the equator. During 1994, maximum amplitudes of the intraseasonal oscillation are 20 m s-1 in January and 30 m s-1 in June. The intraseasonal variability present in HRDI winds is qualitatively consistent with variations on similar timescales reported at Christmas Island. It has been hypothesized that the wind patterns at Christmas Island result from modulated gravity wave driving [Eckermann et al., 1997]. The results of the present study strongly support this view.