A global climatological study of the ionospheric foF2 and hmF2 covariance

The ionosphere exhibits significant day-to-day variability. This is not currently captured in empirical climatological models, which provide a monthly average ionosphere. In this paper, we study the global variance and covariance between the peak plasma frequency (foF2) and the peak height (hmF2) of the ionospheric F2 layer. This provides information about how much the observed F2 layer may differ from the monthly average under quiet to moderate geomagnetic conditions. Clear latitudinal, seasonal and diurnal trends were identified in the foF2 and hmF2 variance and covariance. In general, the foF2 relative variability was larger than that of hmF2, and both peaked at night at equatorial and auroral latitudes. The covariance was usually positive during the day, except at the magnetic equator, and negative at night, except at mid latitudes. The solar cycle did not have a strong impact on the relative variability in the foF2 and hmF2, such that the absolute variability generally scaled proportionally to the changes in the monthly median foF2 and hmF2 over the solar cycle.