ULF wave effects on high frequency signal propagation through the ionosphere

Abstract. Variations in the total electron content (TEC) of the ionosphere alter the propagation characteristics of EM radiation for frequencies above a few megahertz (MHz). Spatial and temporal variations of the ionosphere TEC influence highly sensitive, ground based spatial measurements such as those used in radio astronomy and Global Positioning System (GPS) applications. In this paper we estimate the magnitudes of the changes in TEC and the time delays of high frequency signals introduced by variations in the ionosphere electron density caused by the natural spectrum of ultra-low frequency (ULF) wave activity that originates in near-Earth space. The time delays and associated phase shifts depend on the frequency, spatial structure and amplitude of the ULF waves.