The lowest mesopause temperature in 1996 and 1997 at 23°S Original Research Article

From the long period airglow data at Cachoeira Paulista (22.7°S, 45.0°W), from 1990 to 1999, unusually low level of the OH rotational temperature was observed in 1996 and 1997. Compared to the other temperature observation results, it is concluded that it was lower than that expected from the solar cycle trends. A possible relation of the mesopause temperature and the atmospheric wave activities (gravity, tidal and Kelvin waves) is discussed.