Modeling the low latitude thermosphere and ionosphere

The National Center for Atmospheric Research (NCAR) thermosphere/ionosphere/ electrodynamic general circulation model (TIEGCM) is one of the few models that self-consistently solves the coupled equations for the neutral atmosphere and ionosphere. Timely questions are how well the TIEGCM currently simulates the low latitude ionosphere and what modifications might bring about better predictions. Comparisons between data obtained in and around Jicamarca, Peru, near the magnetic equator, and simulations with the TIEGCM indicate good progress has been made but reveal some serious discrepancies and inadequacies. Good to excellent agreement is obtained for electron densities, electron and ion temperatures, and nmax. The agreement is only fair to poor for hmax, zonal drifts, the 630 nm nightglow, and the horizontal neutral winds. The most important discrepancy is the simulated neutral temperature, which is at least 100 K too cold relative to the FPI observations. Increasing the EUV fluxes in the model to improve prediction of the model temperature also improves representation of the airglow observations and the ionosphere, for which the model typically underrepresents the electron densities. The discrepancy in neutral temperature is also present in comparisons with the empirical model MSIS which represents the largest database of thermospheric temperature measurements. Since the neutral and ionized atmospheres are tightly coupled at low latitudes, simultaneous measurements of neutral and ion parameters, preferably over an extended time period, would be invaluable to further the understanding of the region. Better knowledge of the EUV fluxes and the high altitude O+ fluxes may also help resolve some of the model/data discrepancies.