Coherent changes of solar and ionospheric activity during long-lived coronal mega-hole from Carrington rotation CR2165 to CR2188

Correlations of solar and ionospheric activity are investigated during the long-lived coronal mega-hole (CMH) for 24 solar rotations at the decline phase of SC24 from June, 2015, to March, 2017. Pch index (Luo et al., 2008) which is a function of the intensity in the central area developed for forecasting of daily solar wind speed (Vsw) is used as characteristic of efficiency of CMH. The solar activity indices Pch, SSN2, F10.7, Lyman-α, MgII, Vsw, and the ionospheric indices - global electron content GEC and global noon TECgn index averaged from data of 288 IGS observatories are analyzed. Sporadic disturbances in solar and ionospheric data are smoothed by the time-weighted exponential accumulation of their history with the persistence factor τ (0 ≤τ < 1) for the preceding 27 days. Growing coronal hole power Pch(τ) during the CMH life is observed while all other solar and ionospheric indices are decreasing at the decreasing phase of SC24. The solar wind speed near the Earth is diminishing from CR2165 to CR2174 but growing afterwards. Delayed correlation of solar wind speed Vsw(τ) with Pch(τ) shows lag (delay) of Vsw(τ) by 4 days relative Pch(τ) index while the ionospheric data don't show any delay. Examination of relations of the ionosphere activity with the solar and ionospheric global indices is made with noon measurements of the foF2 critical frequency and total electron content TEC at eight observatories (4 from the northern hemisphere and 4 from the southern hemisphere). The best linear correlation of foF2(τ) and TEC(τ) at selected sites is obtained with GEC(τ) and TECgn(τ) indices (the correlation coefficient ρ from 0.7 to 0.9 in the most cases) so that TECgn(τ) and GEC(τ) global indices could serve as potential candidates for driving the ionospheric model in the real time regime.