Correlation coefficients at 1st July each year (1998–2020) between Em_sw and TEC (first panel), foF2 (second panel), hmF2 (third panel), and equivalent slab thickness (last panel). Correlation coefficients at high solar activity (one-year moving average of F10.7 > 120 sfu) are red, low solar activity (one-year moving average of F10.7 < 80 sfu) are blue and other correlation coefficients are grey.