  The total ionospheric content (TEC) over the Iberian Peninsula was studied
using data from two locations obtained both by GNSS receivers and an ionosonde.
The principal component analysis applied to the TEC data allowed us to extract
two main modes. Each mode is characterized by daily TEC variation of a certain
type (PC) and its amplitude for each of the studied day (given by the empirical
orthogonal functions, EOF). The variations of these modes as well as the
original TEC data were studied in relations to four strongest geomagnetic
storms of 2015 and three geomagnetic disturbances of lower amplitude observed
during the same months. EOFs were found to correlate well with space weather
parameters characterizing solar UV and XR fluxes, number of the solar flares,
parameters of the solar wind and geomagnetic indices. Multiple regression
models were constructed to fit EOFs using combinations of the space weather
parameters with a lag from 0 to 2 days. Combining the regression models of EOFs
with the corresponding PCs we reconstructed TEC variations as a function of
space weather parameters observed in previous days. The possibility to use such
reconstructions for the TEC forecasting was also studied.
