Solar Atmospheric Tides
The largest amplitude atmospheric tides are generated by the periodic heating of the atmosphere by the Sun – the atmosphere is heated during the day and not heated at night. This regular diurnal (daily) cycle in heating generates tides that have periods related to the solar day. It might initially be expected that this diurnal heating would give rise to tides with a period of 24 hours, corresponding to the heating's periodicity. However, observations reveal that large amplitude tides are generated with periods of 24 and 12 hours. Tides have also been observed with periods of 8 and 6 hours, although these latter tides generally have smaller amplitudes. This set of periods occurs because the solar heating of the atmosphere occurs in an approximate square wave profile and so is rich in harmonics. When this pattern is decomposed into separate frequency components using a fourier transform, as well as the mean and daily (24-hr) variation, significant oscillations with periods of 12, 8 and 6 hrs are produced. Tides generated by the gravitational effect of the sun are very much smaller than those generated by solar heating. Solar tides will refer to only thermal solar tides from this point.
Solar energy is absorbed throughout the atmosphere some of the most significant in this context are water vapor at (~0–15 km) in the troposphere, ozone at (~30 to 60 km) in the stratosphere and molecular oxygen and molecular nitrogen at (~120 to 170 km) in the thermosphere. Variations in the global distribution and density of these species results in changes in the amplitude of the solar tides. The tides are also affected by the environment through which they travel.
Solar tides can be separated into two components: migrating and non-migrating.
Read more about this topic: Atmospheric Tide
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