Implication of the ionosphere in low latitude micropulsations

Abstract

The low frequency hydromagnetic waves in the terrestrial magnetosphere, known as geomagnetic micropulsations, have to propagate through the ionosphere before they are detected on the ground. It is generally argued that the polarization suffers a 90° rotation while it crosses the ionosphere. All ground data are analysed on this premise. The arguments put forward to this theory have been briefly reviewed and it has been shown that this is not always true, certainly not in the low latitude ionosphere. A general expression is then derived for the low latitude ionospheric effects demonstrating that the rotation angle is substantially different from <img src='/image/spc_char/pi.gif' border=0>/2. Moreover, the amount of rotation is a function of the direction of the wave field. Since the transformation matrix is a complex quantity the ionosphere also introduces phase change among the two horizontal components. Thus the nature of polarization also changes as the wave penetrates the ionosphere.