Browsing by Author "Huang, C. M."

Now showing 1 - 2 of 2
  • Thumbnail Image
    ItemRestricted
    Longitudinal variations of positive dayside ionospheric storms related to recurrent geomagnetic storms
    (American Geophysical Union, 2013-10-31) Dmitriev, A. V.; Huang, C. M.; Brahmanandam, P. S.; Chang, L. C.; Chen, K. T.; Tsai, L. C.
    We have performed an analysis of case events and statistics of positive ionospheric storms in the dayside region of the equatorial ionization anomaly during recurrent geomagnetic storms (RGSs), which dominate in geomagnetic and ionospheric conditions on the declining phase of solar activity in 2004 to 2008. It is shown that total electron content (TEC) has a tendency to minimize before the beginning of RGSs and to peak 3 to 4 days after, i.e., on the RGS recovery phase produced by high‐intensity long‐duration continuous auroral activity. The maximum of TEC coincides with the maximum of solar wind velocity within high‐speed solar wind streams. An analysis of electron content vertical profiles, derived from two independent methods using ionosondes and Constellation Observing System for Meteorology, Ionosphere, and Climate /Formosa Satellite mission‐3 radio occultation, showed that in the maximum of an ionospheric storm on 28 March 2008, the F2 layer thickens, NmF2 increases by ~50%, and hmF2 elevates by a few tens of kilometers. The response of positive ionospheric storms to solar, heliospheric, and geomagnetic drivers reveals a prominent longitudinal asymmetry. In the longitudinal range from −90° to 90°, the solar illumination plays a major role, and in the range from 90° to −120°, the influence of heliospheric and geomagnetic drivers becomes significant. The highest correlations of the TEC enhancements with the heliospheric and geomagnetic drivers were found during December–February (r increased from ~0.3 to ~0.5). We speculate that the dynamics controlling this might result from an effect of solar zenith angle, storm time effects of thermospheric ΣO/N2 enhancement, and penetrating electric fields of interplanetary and magnetospheric origin.
    Palabras clave:Ionospheric stormsRecurrent magnetic stormsCorotating interaction regions
  • Thumbnail Image
    ItemRestricted
    Theoretical effects of geomagnetic activity on low-latitude ionospheric electric fields
    (American Geophysical Union, 2005-05-27) Huang, C. M.; Richmond, A. D.; Chen, M. Q.
    The influence of geomagnetic activity on middle‐ and low‐latitude thermospheric winds and ionospheric electric fields is investigated using model results from the National Center for Atmospheric Research Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model. Model runs are made for different levels of geomagnetic activity. Model results show that the equatorward ionospheric currents produced by disturbance winds develop positive charge accumulation at low latitudes that maximizes in the premidnight sector. The local time of maximum electric potential perturbation depends significantly on universal time so that the local time of reversal of the equatorial zonal perturbation electric field varies with longitude by 2 to 3 hours, depending on the intensity of geomagnetic activity. The westward perturbation electric field in the postsunset period indicates that stronger geomagnetic activity will produce a lower driven height of the evening F region. After geomagnetic activity ceases, model results show that the zonal disturbance winds can last for many days in the postrecovery period, while the meridional disturbance winds decay more rapidly. The long‐lasting zonal winds, through the Pedersen currents they drive, help maintain meridional disturbance potential drops that decay much more slowly than the zonal disturbance potential drops after the activity ceases.
    Palabras clave:Ionospheric disturbanceGeomagnetic activityElectrodynamics