Previous studies showed that an intraseasonal oscillation (ISO) is present in the equatorial mesosphere and lower thermosphere (MLT) region. The ISO in the equatorial MLT region was first recognized by Vincent (1994) andEckermann et al. (1997), who performed spectral analyses of medium-frequency (MF) radar observations for several years at Christmas Island (2°N, 157°W). They found a zonal wind amplitude of 20 m s −1 and an oscillation period of ∼60 d in the altitude range of z = 85-90 km. They also showed that the phase of the zonal wind components descends with time. The ISO has also been observed by MF and meteor radars at other longitudes in the tropics. Rao et al. (2009) investigated simultaneous observations of daily mean zonal wind at the height of 88 km by the meteor radars at Cariri (7.4°S, 36.5°W) and Ascension Island (7.9°S, 14.4°W) and two MF radars at Tirunelveli (8.7°N, 77.8°E) and Pameungpeuk (7.7°S, 107.7°E) over 1.5 years. They found that, for the ISO fluctuations with periods of 20-100 d, the phase difference between the four longitudinally separated radar sites is quite small. They also reported that the ISO is amplified during the solstice season, which corresponds to the westward phase of the mesospheric semiannual oscillation (MSAO). Guharay et al. (2017) reported the quasi-27-day oscillation using zonal winds observed by the meteor radars at Sao Joao do Cariri (7.4°S, 36.5°W), Cachoeira Paulista (22.7°S, 45°W), and Santa Maria (29.7°S, 53.7°W) in the height range of z = 81-99 km.