B. R. Clemesha, P.P. Batista and D. M. Simonich

Instituto Nacional de Pesquisas Espaciais (INPE), CP 515, São José dos Campos, 12201-970 SP, Brazil.

The INPE lidar has been used to make extensive studies of the atmospheric sodium layer. The vertical distribution of sodium is strongly influenced by atmospheric waves and, consequently, measurements of the time-variation of this distribution can be used to study atmospheric dynamics. In the past we have used measurements of this sort to determine the principal tidal modes active at the our location (São José dos Campos, 23° S, 46° W). In principal, diurnal and semi-diurnal oscillations can be produced both by solar tides and by solar zenith angle-dependent photochemical effects, and some workers have suggested that photochemistry dominates such variations. Recent 24-hour lidar observations, made in conjunction with meteor radar measurements of the winds in the 80 - 105 km region, show a very strong correlation between the winds and the variations in sodium density, strongly suggesting that the latter are mainly the result of tidal oscillations rather than photochemical effects, and thus justifying the derivation of tidal modes from the lidar measurements.