Abstract
Using the VHF radar (49.92 MHz) at Jicamarca (12.0°S, 76.9°W), radio wave scattering from the tropical mesosphere was observed for more than 60 hours on November 14–16, 1977. The 60‐ to 90‐km region was probed at 2.5‐km intervals in two antenna beam directions: the vertical and 3.45° from the zenith to the west. Strong aspect sensitive scattering that is accompanied by a marked positive correlation between the temporal variation of the echo power and the signal correlation time is observed below about 75 km as in previous measurements. Above that altitude, the correlation becomes negative while the scattering is virtually isotropic. This difference appears to be directly related to the stability of the atmosphere, and enhanced reflectivity regions seem to be narrow structures that are horizontally stratified below 75 km. The rms turbulent velocity fluctuations generally increase above 75 km. Signal correlation time depends upon the period of data used to calculate power spectra in the period of 10–60 s, suggesting that there exist substantial velocity fluctuations on short time scales.
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