The high-power VHF radar technique is a powerful tool to lnvestigate winds and turbulence in the middle atmosphere. However, an entire wind or power profile from the upper troposphere to the lower thermosphere. (10-100 km) has not yet been obtained.- Especially, it is very difficult to observe the so-called ''gap region" from 35 to 60 km due to weak echo power. Recently, the Jicamarca VHF radar facility (50 MHz) in Peru has been greatly improved, and a height resolution of 250-500 m is now achieved by pulse compression using 16- or 32-bit complementary codes. This paper presents a preliminary result of Jicamarca radar observations of the upper stratosphere and lower mesosphere, including the "gap region'', conducted on Sept. 24-28, 1990.

Recent E region VHF backscatter echoes ob­served by the MU radar at mid-latitudes show quasi­periodic striations with a fairly constant range vs. time tilt in a RTI display. These features are explained in terms of gravity waves with frequencies close to the Brunt-Väisälä frequency which modulate the shape of sporadic E layers. The conditions of instability, when the magnetic field has a significant dip angle, is revised. Differing from previ­ous work, we argue that conditions of local gradient drift instability are not sufficient and one has to consider the integrated properties of each magnetic filed tube. Strat­ified sporadic E layers are stable using this new criteria, unless they are distorted to produce unstable integrated gradients. Gravity waves with phase fronts parallel to the magnetic dip angle are capable of producing such distor­tion, imposing its own temporal and sp...

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...

We present a method for deriving horizontal velocities, vertical velocities, and in-beam incidence angles from radar interferometer data. All parameters are calculated from the slope and intercept of straight lines fitted in a least-squares sense to the variation of the signal phase as a function of radial velocity for each pair of receiving antennas. Advantages of the method are that the calculations are computationally fast and simple, and the analysis leads to relatively simple expressions for the uncertainty in the velocity measurements.

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...