Ionospheric quasi-biennial oscillation in global TEC observations

• Ionospheric QBO appears during solar maximum, with the period of 22–34 months.
• Ionospheric QBO exists in all latitudes from 50°S to 50°N.
• The transition of QBO phases occurs earlier in high latitudes than equatorial region.
• The correlation coefficient between ionospheric QBO and stratospheric QBO is 0.704.

The total electron content (TEC) observations were analyzed for the ionospheric quasi-biennial oscillations (QBO) during the period of 1999–2011 in a global perspective. Zonal and monthly means of TEC data were calculated to reveal the global characteristics and long-period variations in ionosphere. The Lomb–Scargle periodogram methods and wavelet spectral analysis were applied to the residuals of TEC, which are obtained from subtracting the fittings with solar index, F10.7. The ionospheric QBO signal only appears during solar maximum, existing in all latitudes from 50°S to 50°N, and the period is within 22–34 months. In the equatorial region, the QBO exhibits a significant feature of equatorial ionospheric anomaly (EIA), where the transition of phases occurs 2–6 months later than in high latitude. The correlation coefficient with the stratospheric QBO reaches 0.704. It can be assumed that stratospheric QBO influences the QBO phenomenon in ionosphere; nevertheless, the present results do not permit one to conclude the mechanism.