Variations in the Radial Dependence of the Interplanetary Scintillation Level in the Descending Phase of Solar Cycle 24.

The results of the long-term (2015–2019) series of interplanetary scintillation observations carried out with the LPA LPI radio telescope at the frequency 111 MHz are presented. We analyzed the radial dependences of the relative level (index) of interplanetary scintillations of the radio source 3C 48, the line of sight to which during the year shifts from low to medium and high heliolatitudes. For all annual series, we showed that the radial dependence of the scintillation index turns out to be flatter than expected for the model of a spherically symmetric medium. The difference is explained by the latitudinal effect, considering the influence of the near-equatorial layer with an increased plasma density. Modeling the low-latitude layer shows that the layer thickness at the phase of the decline in solar activity is, on average, two times greater than near the activity minimum. [ABSTRACT FROM AUTHOR]