RADAR OBSERVATIONS OF GRAVITY-WAVES OVER JICAMARCA, PERU DURING THE CADRE CAMPAIGN

We present results obtained with the mesosphere-stratosphere-troposphe re (MST) radar at Jicamarca, Peru, from three 10-day experiments in Ja nuary 1993, March 1994, and August 1994. Horizontal and vertical veloc ities were measured over ranges spanning the lower part of the stratos phere and most of the mesosphere. In the stratosphere, the fluctuating part of the wind field was found to be dominated by inertia-gravity w aves. Sinusoids of different period were fit to the velocity time seri es using a least squares procedure. The dominant periods of the inerti a-gravity wave motions were found to be 1.5 days for the January 1993 experiment and 2.1 days for the August 1994 experiment. For the Januar y 1993 experiment, the amplitudes and phases of the inertia-gravity wa ve oscillations were extracted for the vertical as well as the horizon tal components. The vertical amplitude of the 1.5-day period wave was small (<0.1 m s(-1)), but measurable with the Jicamarca radar. The int rinsic periods of the inertia-gravity waves were inferred from the fit s using two different methods. The first method predicted the intrinsi c period using the orbital ellipses traced out in time by fits to the horizontal winds. The second method used information taken from the ve rtical as well as the horizontal fits. The values of intrinsic period made using the second method were found to have much less scatter than the values inferred solely from the orbital ellipses. The momentum fl ux estimates in both the stratosphere and mesosphere were found to dep end significantly on the exact methodology used. A technique was adopt ed whereby estimates were formed only when radial velocities were meas ured simultaneously on both beams of a coplanar beam pair. Most of the total wave stress was usually contributed by waves at periods greater than or equal to 4 hours in the stratosphere and greater than or equa l to 1 hour in the mesosphere. Ln the stratosphere, localized layers o f enhanced momentum flux were sometimes observed. The obvious anticorr elation between the shear of the mean wind and the momentum flux in th ese layers suggests that they were caused by in situ generation of wav es by the Kelvin-Kelmholtz instability, rather than gravity waves prop agating from lower levels. At short periods, momentum flux spectra in the stratosphere and mesosphere showed numerous positive and negative peaks. A correlation analysis revealed that the high-frequency peaks w ere associated with discrete wave packets. The short-scale waves assoc iated with these packets were fairly isotropic in their direction of p ropagation, and due to cancellation they contributed little net moment um.