Seasonal and latitudinal differences of the saturation effect between ionospheric NmF2 and solar activity indices

In the equatorial anomaly region, the saturation effect is stronger, and the equinox has the strongest saturation effect. All seasons considered, the equatorial anomaly region has the strongest saturation effect, followed by the magnetic equatorial region. The saturation effect becomes relatively weak at middle latitudes.

At higher latitudes and in the Northern Hemisphere, there is even a trend of nonlinear increase of N m F 2 with solar activity. Our results indicate that thermospheric global circulation is probably an important factor that introduces seasonal, latitudinal, and north-south differences in the correlations between N m F 2 and solar activity indices.