| dc.description.abstract | Long-term radio occultation (RO) observations sounded by of FORMOSAT-3/COSMIC provide an excellent opportunity to investigate plasma structures and dynamics of the ionospheric F2-layer during the sunrise period. In total, there are more than 4,000,000 RO electron density profiles from April 2006 to December 2017. The seasonal, longitudinal, and solar activity variations of, the F2-peak height, hmF2, and electron density, NmF2, are examined during the sunrise period. Results show the hmF2 and NmF2 are higher during the high solar activity period than in the lower one. Both hmF2 and NmF2 yield hemispheric symmetry in Spring and Autumn equinox. On the other hand, 1-2.5 hours before the local sunrise, which is termed pre-sunrise ascension, the hmF2 ascends 20-30 km especially at mid-latitudes at about ±20°N in the winter hemisphere during the high solar activity period. The F2-layer starts ascending 30 minutes earlier than the usual in equinox, and becomes unclear in local summer. Meanwhile, the F2-layer ascending becomes not obvious when magnetic declination is negative or the earth’s magnetic field deflects westward. The F2-layer uplift followed by a sudden descend is attribute to the downward movement of the ionization peak during sunrise, which might result in the conjugate effect or the neutral wind effect. | en_US |