The effect of ∼27 day solar rotation on ionospheric F₂ region peak densities (NmF₂)

They accounted for more than 85% of the variations seen in the NmF₂ ∼27 day variation, and their contributions became about 95% at higher latitudes. At geomagnetically low latitudes, the contribution of the ∼27 day variation in solar EUV radiation was greater than that of the ∼27 day variation in geomagnetic activity. However, the contribution from geomagnetic activity became more significant and was even larger than the contribution of solar radiation at higher latitudes, especially at midnight.

At all latitudes the correlation between the ∼27 day variations of NmF₂ and solar radiation was evidently positive, whereas that between NmF₂ and geomagnetic activity was positive at geomagnetically low latitudes and became negative at higher middle latitudes. We did not found large seasonal or solar cycle changes in the ∼27 day variations of NmF₂. These variations, however, did show significant differences between the two hemispheres.