[[spi:math]] (33) [[spi:math]] is sometimes referred to as the Alfven wave transit time [[spi:math]] . Even though the exact solution (28) - (33) looks complicated, the interpretation turns out to be very simple. Examination of (28) shows that contributions to the Alfven wave velocity field are made up of two terms of opposite sign, with the negative contribution being associated with an extra factor of [[spi:math]]. Since [[spi:math]] is the ionospheric reflectance for the Alfven wave, i.e., the fraction of wave amplitude reflected by the dissipative conducting ionosphere, we can interpret the positive term of (28) to be due to Alfven waves arriving at the space-time point (zi, t) from the equator while the negative term is due to Alfven waves arriving from the ionosphere, having been reflected once more than the corresponding waves of the positive term. Now the structure of (29) has three significant elements: (1) it consists of an infinite sum of contributions, (2). each contribution is causal (as indicated by the Heaviside function [[spi:math]]), and (3) each contribution has been reflected q times from the ionosphere (as indicated by the factor [[spi:math]]). Examination of (30) with [[spi:math]] and [[spi:math]] indicates that the former is the arrival time at zi from the direction of the equator of an Alfven wave which has been reflected q times from the ionosphere, whereas the latter is the arrival time at zi from the direction of the Alfven wave which has been reflected (q+1) times. The two contributions are 180° out of phase because one is propagating in the opposite direction from the other. If the reflectance of the ionosphere is low [[spi:math]], the Alfven wave field decays with time constant [[spi:math]] after the 26
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