Morphological study on the ionospheric variability at Bharati, a polar cusp station in the southern hemisphere

Morphological features of the quiet/disturbed time variations in the Total Electron Content (TEC) at the polar cusp station Bharati (76.69\textdegreeS MLAT) during a period of 5 years starting from February 2013 to December 2017 has been studied using GPS TEC measurements. The TEC at Bharati follows a diurnal pattern with its peak appearing close to local noon/magnetic noon during the summer/winter months. A nighttime enhancement in the TEC is seen around the magnetic midnight during winter. The plasma density at Bharati also exhibits semi-annual variation and a strong dependence on solar activity. A comparison of the IRI 2016 model derived TEC and the GPS TEC at Bharati shows significant differences with large underestimation of TEC especially during the nighttime period of the winter months. A two fold difference in magnitude between the GPS and modeled TEC is also observed in the summer months of the high solar activity period of 2013\textendash2015. The response of the TEC to geomagnetic storms is found to depend on the onset time of the storm. We show that the morphological features in the temporal evolution of the plasma density at Bharati vary as the location of Bharati changes from being inside the polar cap, to the auroral region, and to the polar cusp in quick succession in a day. Our results highlight the fact that the dynamic nature of the location of Bharati with respect to the position of the polar cap plays an important role in deciding the plasma distribution at the polar cusp station.