Ionospheric irregularities at low latitude using VHF scintillations during extreme low solar activity period (2008–2010)

Abstract

In the present study, we have used 250 MHz radio signal radiated by geostationary satellite UFO-02 to study the occurrence characteristics of very high frequency scintillations associated with ionospheric irregularities during recent extreme low solar activity period from 2008 to 2010 at low latitude Indian station Varanasi (Geomag. latitude = 14°55′N, long. = 154°E, Dip angle = 37.3°, Sub-ionospheric dip = 34°). The impact of this recent extreme low solar activity period on ionosphere is investigated. It is observed that the scintillation occurrence is low having maximum percentage occurrence during pre-midnight periods. With increasing interest in understanding the behavior of ionospheric irregularities, an effort has been made to examine also the influence of solar and magnetic activity over the occurrence of scintillations. During the extreme low solar activity years the scintillation occurrences do not vary linearly with the sunspot number. The inhibition and generation of irregularities during enhanced magnetic activity period are explained by considering changes in the electric field. The spectral analysis provide spectral index for irregularities which varied between −1.5 and −8 and characteristic length of irregularities varied between 400 and 1200 m which confirms that 250 MHz scintillations observed over Varanasi were associated with intermediate scale irregularities. © 2016, Akadémiai Kiadó.