Internal gravity waves are known to play an important role in dynamics of the middle atmosphere. They can transport momentum flux from lower atmosphere to upper atmosphere and sometimes break mean flows or large-scale long-period motions due to dissipation process associatcd with wave flow interaction. However, an entire profile of short period gravity waves has not yet been obtained, since it has been very difficult to detect extremely weak atmospheric echoes from so-called "gap region" of 30-60 km heights. Recently, the Jicamarca VHF radar system in Peru ( Woodman and A.Guillen, 1974), which is one of the largest high-power VHF /UHF radars in the world, has been greatly improved in height resolution, and reliable atmospheric echoes have been, for the first time, detected in the gap regían by the Jicamarca radar with the high-altitude resolution (500 m). This paper presents new observa...

High-resolution upper tropospheric and lower stratospheric (5-30 km) wind data were obtained during three periods from 1979 to 1981 with the aid ofthe high-power UHF radar at Arecibo, Puerto Rico (18.4°N, 66.8°W). A quasi-periodic wind oscillation with ai;t apparent period of 20-50 h was observed between 16 and 20 km in every experiment.The amplitude of both zonal and meridional wind components was ~2 m s-1, and the vertical wavelength ~2 km. The direction of the wind associated with this oscillation rotated clockwise with time, as seen for inertia-gravity waves in the Northern Hemisphere. The wave disappeared near 20 km where the mean zonal flow had easterly shear with height. This phenomenon is discussed in terms of wave absorption at a critical leve!. lt is suggested that the wave had a westward horizontal phase speed of 10-20 m s-1. The intrinsic period and the horizontal wavelengt...

A cooperative synchronous observation of winds in the tropical lower stratosphere and mesosphere was carried out using VHF radars at Jicamarca (11.95°S, 76.87°W) and at Arecibo (18.35°N, 66.75°W) on 19-21 or 23 November 1981. The comparison between observations about symmetrical north and south of the equator is focussed on the mean and tidal wind characteristics. Vertical structures of the mean zonal winds at both observational stations are in fairly good agreement with the CIRA (1972) zonal circulation model at the corresponding latitudes. The nature of lower stratospheric diurnal tides is similar between Jicamarca and Arecibo. Their vertical profiles generally correspond to the theoretical predictions based on the fundamental tidal modes. The vertical scale of the tidal components including higher-order modes is shown to be longer than 10km. In the mesosphere, vertically propagati...