Anomalous electron density events in the quiet summer ionosphere at solar minimum over Millstone Hill

This study compares the observed behavior of the F region ionosphere over Millstone Hill with calculations from the IZMIRAN model for solar minimum for the geomagnetically quiet period 23±25 June 1986, when anomalously low values of hmF 2…<200 km) were observed. We found that these low values of hmF 2 (seen as a G condition on ionograms) exist in the ionosphere due to a decrease of production rates of oxygen ions resulting from low values of atomic oxygen density. Results show that determination of a G condition using incoherent scatter radar data is sensitive both to the true concentration of O‡ relative to the molecular ions, and to the ion composition model assumed in the data reduction process. The increase in the O‡ ‡ N 2 loss rate due to vibrationally excited N2 produces a reduction in NmF 2 of typically 5±10% , but as large as 15% , bringing the model and data into better agreement. The e€ect of vibrationally excited NO‡ ions on electron densities is negligible.