On the relation between geomagnetism and the circulatory motions of the air in the atmosphere

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Abstract
General considerationsThe dynamo‐theory of the diurnal variation of the Earth's magnetic field offers an explanation of this phenomenon that is expressed in terms of diurnal motions of the air in the high atmosphere. These motions must be related, even if very indirectly, to the air‐flow below through the changes of horizontal pressure‐distribution, shear, and the vertical movements of the air that in some degree must accompany all of these motions. The altitudes in which occur the air‐motions that generate the electromotive forces and the atmospheric‐electric currents of the dynamo‐theory are not surely known, but that they lie far above those accessible to sounding‐balloons seems certain. Perhaps the best estimate of the altitudes at which these atmospheric‐electric currents flow may be had from the requirement that, at these altitudes there be sufficient molecular collisions and at the same time sufficient ionization that the direct‐current conductivity of the air be relatively large. As an approximate estimate of this it seems that an altitude at the base of or somewhat below theE‐layer of the ionosphere may be taken, which, as an abbreviation to aid in discussion, will be spoken of in the present work as the 60‐ to 80‐km region. How far below this a relation can still be perceived between the air‐motions occurring there and those below remains to be discovered.

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