Browsing by Author "Lu, G."

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    Ionospheric and thermospheric variations associated with prompt penetration electric fields
    (American Geophysical Union, 2012-08-10) Lu, G.; Goncharenko, L.; Nicolls, M. J.; Maute, A.; Coster, A.; Paxton, L. J.
    This paper presents a comprehensive modeling investigation of ionospheric and thermospheric variations during a prompt penetration electric field (PPEF) event that took place on 9 November 2004, using the Thermosphere‐Ionosphere‐Mesosphere Electrodynamic General Circulation Model (TIMEGCM). The simulation results reveal complex latitudinal and longitudinal/local‐time variations in vertical ion drift in the middle‐ and low‐latitude regions owing to the competing influences of electric fields and neutral winds. It is found that electric fields are the dominant driver of vertical ion drift at the magnetic equator; at midlatitudes, however, vertical ion drift driven by disturbance meridional winds exceeds that driven by electric fields. The temporal evolution of the UT‐latitude electron density profile from the simulation depicts clearly a super‐fountain effect caused by the PPEF, including the initial slow‐rise of the equatorial F‐layer peak height, the split of the F‐layer peak density, and the subsequent downward diffusion of the density peaks along magnetic field lines. Correspondingly, low‐latitude total electron content (TEC) becomes bifurcated around the magnetic equator. The O/N2column density ratio, on the other hand, shows very little variations during this PPEF event, excluding composition change as a potential mechanism for the TEC variations. By using realistic, time‐dependent, high‐latitude electric potential and auroral precipitation patterns to drive the TIMEGCM, the model is able to successfully reproduce the large vertical ion drift of ∼120 m/s over the Jicamarca incoherent radar (IS) in Peru, which is the largest daytime ion drift ever recorded by the radar. The simulation results are validated with several key observations from IS radars, ground GPS‐TEC network, and the TIMED‐GUVI O/N2column density ratio. The model‐data intercomparison also reveals some deficiencies in the TIMEGCM, particularly the limitations imposed by its upper boundary height as well as the prescribed O+ flux.
    Palabras clave:Disturbance neutral windIonospheric variationsPenetration electric fields
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    Modeling ionospheric super‐fountain effect based on the coupled TIMEGCM‐SAMI3
    (American Geophysical Union, 2013-04-02) Lu, G.; Huba, J. D.; Valladares, Cesar
    Recently, efforts have been undertaken to develop a coupled thermosphere‐ionosphere‐plasmasphere model based on two well‐established models, namely, the Thermosphere‐Ionosphere‐Mesosphere General Circulation Model (TIMEGCM) developed at the National Center for Atmospheric Research and the SAMI3 ionosphere model developed at the Naval Research Laboratory. This paper presents the first results from the coupled model on the investigation of a prompt penetration electric field (PPEF) event that took place on 9 November 2004. The coupled model eliminates two major upper boundary limitations of the stand‐alone TIMEGCM, e.g., the upper boundary height and the prescribed O+ fluxes at the upper boundary. It is found that the F‐layer peak height is raised above 800 km in response to the large PPEF. The O+ fluxes in the top ionosphere vary drastically during the course of the PPEF, with strong upward and downward fluxes with a magnitude greater than 109 cm−2 s−1 in localized regions. For the first time, the coupled model allows us to simulate and visualize the super‐fountain effect on a global scale. Future model development is also envisaged, including the implementation of a more realistic magnetic field model and a fully two‐way coupling between neutrals and ions.
    Palabras clave:Super‐fountain effectGeomagnetic stormIonospheric storm effect