Supplemental reading:

Chapman and Lindzen (1970)

Lindzen and Chapman (1969)

Lindzen (1979)

Lindzen (1967a)

One of the most straightforward and illuminating applications of internal gravity wave theory is the explanation of the atmosphere's tides. To be sure, the theory has to be expanded to include both the sphericity and rotation of the earth.

By atmospheric tides we generally mean those planetary scale oscillations whose periods are integral fractions of a solar or lunar day (diurnal refers to a period of one day, semidiurnal refers to a period of half a day, and terdiurnal refers to a period of one third of a day). These periods are chosen because we know there is forcing at these periods. Gravitational forcing is precisely known; thermal forcing (due in large measure to the absorption of sunlight by O3 and water vapor) is known with less precision. Nevertheless, a situation where forcing of known frequency is even reasonably well known is a situation of rare simplicity, and we may plausibly expect that our ability to calculate the observed response to such forcing constitutes a modest test of the utility of theory.

The situation was not always so simple. There follow sections on the history of this problem and on the observations of atmospheric tides. The history also provides a good example of what constitutes the ‘scientific method’ in an observational science where controlled experiments are not available.

History and the ‘scientific method’

Textbooks in meteorology (and most other sciences) usually treat history (if they treat it at all) as an entertaining diversion from the ‘meat’ of a subject.