Mesospheric winds at equatorial latitudes: a review on observational aspects

Abstract

Our observational knowledge of mesospheric winds at low equatorial latitudes is reviewed including both rocket and radio remote sensing techniques. Although equatorial latitudes are not as densely covered with rocket soundings as middle latitudes, we can say that out knowledge on the periodic components of the wind—in the seasonal and annual time scales—up to 60–65 km is fairly well established. At higher altitudes the data-base provided by both techniques is poor. The behaviour of the tidal components even at the lower altitudes is not well described. It would appear that the tidal components are more random in nature, in disagreement with present theoretical expectations which predict a more deterministic and periodic behaviour. Studies of wind fluctuations in the planetary-wave time scale is nonexistent. Also, very little has been done on the statistical characterization of the residual random fluctuations of the winds at all time scales. The latter becomes specially important at higher altitudes since radio techniques have detected the existence of large random fluctuations at gravity wave periods and a large variability for the tides time from day to day. Radio techniques are very powerful techniques for the study of mesospheric winds and should play an important role in future observations of winds specially at upper mesospheric heights and beyond. Of particular importance is the use of VHF radar scattering from turbulent dielectric fluctuations because of its accuracy, time resolution and continuity of observation.