Oscillations in the atmosphere caused by the influence of the Sun and Moon, predominantly affecting pressure and the wind, and analogous to the more familiar oceanic tides. Although gravitational effects play a part, heating by the Sun is of greater importance. The predominant fluctuation is a semi-diurnal variation in pressure (see diurnal variation), but other periods of 24, 6, and 8 hours are also observed. In the troposphere, the tidal contribution to the wind is negligible, but it increases in the upper atmosphere and may reach 30 m s−1 at around 100 km, where it may become the dominant component.
Subjects: Meteorology and Climatology.