Crucial discrepancy in the balance between extreme ultraviolet solar radiation and ion densities given by the international reference ionosphere model

Abstract

Molecular ions play an important role in the balance of charged particles below the peak density in the F2 region. Balance is determined by ionization of the main neutral constituents by extreme UV solar radiation (EUVSR) and by dissociative recombination of the molecular ions. Using the empirical EUVSR model and the neutral densities given by the MSISE‐90 (Mass Spectrometer‐Incoherent Scatter) model, ionization rates can be calculated using well‐developed, textbook‐level analysis and then compared with the recombination rates corresponding to the molecular ion and electron densities given by the IRI‐2001 and IRI‐2007 empirical models. Our results show that the recombination rates calculated using the IRI model are larger by a factor of 5 to 30 than the ionization rates corresponding to the EUVSR empirical model at altitudes above 190 km at middle and low latitudes and low solar activity. Previously, and for similar reasons, we showed that the IRI predicted 630 nm and 557.7 nm emissions, which were found to be much higher than the observations (Vlasov et al., 2005; Nicolls et al., 2006). The discrepancy greatly increases from noon to dusk and decreases with increasing solar activity. Our results thus show a contradiction between the EUVSR model and the IRI model. Since empirical data on molecular ions are scarce, we argue that straightforward ion chemistry calculations should be added to the IRI to correct the discrepancy.