INFLUENCE OF NONUNIFORM IONOSPHERIC CONDUCTIVITY ON THE GROUND MAGNETIC PERTURBATION ASSOCIATED WITH AN INCIDENT ALFVEN-WAVE

By assuming a simple model of the height-integrated ionospheric conduc tivity with a nonuniformity of sinusoidal type, the influence of the n onuniform ionosphere on the ground magnetic perturbation has been exam ined for the case of Alfven wave incidence. When the characteristic le ngth of nonuniformity, L(c), is greater enough than the height of the ionosphere, d, the effect of non-uniformity is sufficiently large for the incident wave with a horizontal wavelength comparable to or greate r than L(c) and it is not so much dependent on the wavelength itself. On the other hand, when L(c) is of the order of or less than d, the ef fect of non-uniformity does not appear in the observable ground magnet ic perturbation associated with the incident wave with a horizontal wa velength greater enough than d. When L(c) is greater enough than d, it is also found for the incident wave with a horizontal wavelength grea ter than or similar to L(c) and a period greater than or similar to 10 s that the effect of non-uniformity little depends on the period, it increases with the height-integrated conductivity in the range of 10(1 1) to 10(13) esu, it is appreciably significant even for a smaller con ductivity contrast of 1 : 2, and it grows large as the contrast increa ses.