Browsing by Author "Fesen, C. G."

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    Modeling the low-latitude thermosphere and ionosphere
    (Elsevier, 2002-08) Fesen, C. G.; Hysell, D. L.; Meriwether, J. M.; Mendillo, M.; Fejer, B. G.; Roble, R. G.; Reinisch, B. W.; Biondi, M. A.
    The National Center for Atmospheric Research 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. Good-to-excellent agreement is obtained for electron densities, electron and ion temperatures, and nmax. The agreement is fair to poor for hmax, zonal drifts, the oxygen nightglow, and the horizontal neutral winds. The most important discrepancy is in the simulated neutral temperature, which is at least too cold relative to Fabry–Perot interferometer observations. Increasing the EUV fluxes in the model to improve prediction of the model temperature also improves representation of airglow observations and of the ionosphere, for which the model typically underrepresents the electron densities. The disparity 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.
    Palabras clave:ModelingThermosphere dynamicsIonosphere dynamics
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    Simulation of the pre‐reversal enhancement in the low latitude vertical ion drifts
    (American Geophysical Union, 2000-07-01) Fesen, C. G.; Crowley, G.; Roble, R. G.; Richmond, A. D.; Fejer, B. G.
    Low latitude F region ion motions exhibit strong seasonal and solar cycle dependences. The pre‐reversal enhancement (PRE) in the vertical ion drifts is a particularly well‐known low latitude electrodynamic feature, exhibited as a sharp upward spike in the velocity shortly after local sunset, which remains poorly understood theoretically. The PRE has been successfully simulated for the first time by a general circulation model, the National Center for Atmospheric Research thermosphere/ionosphere/electrodynamic general circulation model (TIEGCM). The TIEGCM reproduces the zonal and vertical plasma drifts for equinox, June, and December for low, medium, and high solar activity. The crucial parameter in the model to produce the PRE is the nighttime E region electron densities: densities ≥ 104 cm−3 preclude the PRE development by short‐circuiting the F region dynamo. The E region semidiurnal 2,2 tidal wave largely determines the magnitude and phase of the daytime F region drifts.
    Palabras clave:E regionElectrodynamicsPlasmas