The effects of the lunar tide‐producing force, so clearly recognizable day by day in the oceanic tides, are veiled in the lower atmosphere by much larger non‐tidal movements. Nevertheless, long series of barometric readings have yielded accurate information about the lunar atmospheric tides. Lunar variations have also been found in the geomagnetic force components; they may be called “geomagnetic tides” since these lunar daily magnetic variations ∟ have been linked by the dynamo‐theory with tidal motions in the ionosphere. They are the result of a comparatively simple large‐scale experiment which is performed daily by the Moon on the Earth and which, involving only gravitational forces, is more easily interpreted than the solar daily variations S, in which magnetic effects of the tidal forces are rather inextricably mixed with those produced by simultaneous daily changes in solar‐heat radiation and ionizing power. The study of ∟ yields information about the lunar tidal motions as well as about the changes of total ionization in the ionosphere.
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Bartels et al. (1940) studied this question.