SEASONAL-VARIATIONS IN MESOSPHERIC SODIUM TIDAL ACTIVITY

Diurnal and nocturnal laser radar measurements of mesospheric sodium density at Sao Jose dos Campos, Brazil (23°S, 46°W), show strong oscillations with 12 and 24 hour periods. It is shown that the amplitudes of the oscillations in sodium density and consequently the vertical wind amplitudes, in general, are larger in winter than in other seasons. Above 97 km, the semidiurnal amplitude is larger than the diurnal in winter, of the same order of magnitude at the equinoxes and smaller in summer. The phases of the inferred semidiurnal vertical wind component, above 97 km, show regular propagating equinoxes, but a confused pattern in summer. -from Authors