LIDAR OBSERVATIONS OF GRAVITY-WAVES AND THEIR SPECTRA NEAR THE MESOPAUSE AND STRATOPAUSE AT ARECIBO

The UIUC CEDAR Rayleigh/Na lidar was operated for approximately 160 h on 30 nights in January, March, and April 1989 at the Arecibo Observat ory (19-degrees-N, 67-degrees-W) as part of the AIDA Act '89 Campaign. During this period 38 quasi-monochromatic gravity waves were observed in the stratopause region (25-55 km) and 62 waves were observed in th e mesopause region (80-105 km). The event rates in both regions are ap proximately half those observed at the midlatitude site of Urbana. The characteristics of the waves in both regions are similar. Measured ve rtical wavelengths range from 1.1 to 17 km, vertical phase velocities from -6 to -270 cm s-1, observed periods from 5 min to 65 h, and ampli tudes (relative atmospheric density variations) 0.4% to 17%. The wave amplitudes in the stratopause region are on average half the values fo r waves in the mesopause region with similar periods and vertical wave lengths. Vertical wavenumber spectra of density perturbations in both regions exhibit power-law dependencies with slopes near -3. The magnit udes of the spectra in the stratopause region are typically a factor o f 5 to 10 times smaller than the magnitudes of the mesopause region sp ectra, which is in significant disagreement with the predictions of li near saturation theory. Temporal frequency spectra of density perturba tions in the mesopause region also exhibit power-law dependencies with slopes between -1.5 and -2.0 (mean slope = 1.85 +/- 0.38) for frequen cies smaller than the Brunt-Vaisala frequency and slopes near -3 for f requencies larger than the Brunt-Vaisala frequency. The rms density pe rturbations averaged 1.2% in the stratopause region and 5.2% in the me sopause region. These results are compared with other radar and lidar observations.