Analysis of the nighttime lower ionosphere by monitoring VLF waves propagation in Antarctic

The nighttime lower ionosphere behavior between 2007 to 2011 is studied estimating the nighttime reflection height (hN) from Very Low Frequency (VLF) waves propagation recorded at Brazilian Antarctic Station Comandante Ferraz (EACF). We focus on the long-term solar activity effect on hN. The results show that hN decrease while the solar activity starts to increase suggesting a control of the solar radiation on the nighttime lower ionosphere, and hence, on the electron density at night. Preliminary results show that the nighttime lower ionosphere might be influenced by the 27-days solar rotation and by long-term atmospheric oscillations as Semiannual (SAO) and Annual (AO) oscillations.