Low-Latitude Ionosphere and Thermosphere: Decadal Observations From the CHAMP Mission

Self-consistent physical models of an auroral flux tube are capable of calculating optical emissions and ionospheric state variables for a given set of magnetospheric drivers. The collocation of incoherent scatter radar (ISR) and photometric measurements provides a powerful framework for testing the internal consistency of such models. This chapter considers the invertibility of this forward process as it pertains to an auroral flux tube. It focuses on the problem of estimating the spectrum of primary electrons via inversion of auroral spectral brightnesses in the near infrared, where prompt and near-prompt emissions of atomic oxygen and molecular nitrogen provide maximum sensitivity to the incident energy spectrum over a limited and contiguous free spectral range. The chapter tests the internal consistency by comparing observed ISR state variables with predictions of the same variables derived by optical inversion.