Interplanetary Scintiallation (IPS) of the Radio Source 3C48 During Periods of Low and High Solar Activity

We present a comparative study of three techniques used to estimate the scintillation index using interplanetary scintillation (IPS) observations carried out by the Big Scanning Array (BSA), which operates at a frequency of 111 MHz. These techniques are based on: rms analysis on-source and off-source (classic), Fourier, and wavelet transforms. IPS data are analyzed separately for the period of low solar activity (2007 – 2009), and for the year 2013, near the solar-activity maximum. Our results show that, in general, these methods are equivalent. We analyze the radial dependence of the scintillation index at meter wavelengths during these two periods. It is found that the observed radial dependence of the scintillation index during both periods of U.C. cycle 24 is flatter than the theoretical dependence expected for the case of solar-wind spherical symmetry. This flattening can be explained in terms of the influence of the heliospheric current sheet during the low solar-activity period, and the influence of solar disturbances, such as coronal mass ejections (CMEs), for the high solar-activity period.