Fifteen‐day observation of mesospheric and lower thermospheric motions with the aid of the Arecibo UHF radar

Abstract

An attempt was made to have a continuous observation of the zonal wind component in the tropical mesosphere and lower thermosphere for 15 days of August 1–15, 1980, with the aid of the UHF radar at Arecibo (18°N). By using the wind data, together with additional data obtained from meteorological rockets, meteor radar, and Tiros‐N satellite, analyses were made of the time‐mean zonal wind profile, tides, long‐period waves, and short‐period gravity‐type waves, respectively. There appears a remarkable day‐to‐day variation of the zonal wind throughout the region between 70 and 95 km with a characteristic time scale of about 5 days, indicating the passage of traveling planetary‐scale waves in the summertime tropical middle atmosphere. It was also found that the short‐period oscillation with a time scale of a few 10 min appears intermittently in association with the strong vertical shear of the background flow. This oscillation is considered to be the manifestation of the Kelvin‐Helmholtz type instability in the lower thermosphere.