Response of low-latitude ionosphere to medium-term changes of solar and geomagnetic activity

The paper presents the medium‐term quasi periodic (∼9–27 day) response of middle and low‐latitude ionosphere to solar [F10.7) and geomagnetic (Kp‐index) forcing. The ionospheric response is examined by wavelet analysis of the relative deviations of TEC over Japan for the period of time 2000–2008. It is found that the ∼27‐day rTEC oscillations correlate well with the same oscillations of the solar index F10.7 particularly in the solar maximum and its early declining phase (2001–2005). During the declining phase of solar activity (for example, year of 2005) the Kp‐index variability exhibits additionally strong oscillations with periods 13.5‐ and 9‐days. Similar oscillations are found in rTEC as well but they do not follow the geomagnetic forcing as faithfully as those associated with F10.7. During solar minimum the quasi periodic rTEC variability is shaped mainly by the recurrent geomagnetic activity. An attempt is made to investigate the latitudinal dependence of the ∼9–27‐day rTEC response over Japan as well as the phase relationship between the forcing and response. Key Points Medium‐term TEC variability over Japan is examined During solar maximum a 27‐day TEC variation is clearly linked to EUV radiation Periodic forcing by CIRs emerges in TEC in the declining phase of solar activity