Inter-hemispheric analysis of daytime low ionosphere behavior from 2007 to 2011

The lower ionosphere behavior from 2007 to 2011 is studied using VLF signals propagating over long distances and received at Comandante Ferraz Brazilian Antarctic Station and Atibaia/Brazil. The VLF signals show high day-to-day variations of the mid-day amplitude, which present a clear seasonal behavior occurring predominantly during wintertime in all years. These high VLF amplitude variations show a significant component with 16-day period, which is typical of planetary waves of stratospheric/tropospheric origin. These results reinforced the solar control of the lower ionosphere and the evidence of vertical couplings in the atmosphere-ionosphere system, even during the 24th solar cycle increasing activity.

► The VLF study improved our understanding of the external forcing in the lower ionosphere.
► Low ionosphere shows variation in close association with the 11-year solar Lyman-alpha radiation.
► The forcing of atmospheric origin is predominant during the wintertime.
► The main atmospheric forcing is due to the effect of planetary waves of stratospheric/tropospheric.