The following is a paper by H. Aspden published in Speculations in Science and Technology, v. 4, pp. 314-316 (1981).
Abstract: The origin of the Earth's electric field is discussed and shown to be a consequence of the selective absorption of solar primary and secondary radiation by electrons in the substance of the Earth's surface and atmosphere.
Commentary: This paper reiterates the viewpoint expressed by the author on this subject in his 1972 book 'Modern Aether Science'.