| Summary: | 碩士 === 國立中央大學 === 太空科學研究所 === 101 === On the basis of GPS radio occultation (RO) technique, we develop a method
to extract ionospheric sporadic E (Es) layer from COSMIC-measured ionospheric
data (e.g., GPS signal signal-to-noise ratio, L1 and L2 excess phases and
RO-retrieved electron density) to investigate the climatology of the Sporadic E
layer.
The results show that there is salient summer-winter asymmetry in the
occurrence rate of the Es layer, namely, higher in summer hemisphere and
lower in winter hemisphere. In addition, there is a strong tendency for the Es
layer to descend with local time that is in harmony with the diurnal or
semi-diurnal tidal motion, depending on season and latitude region. In order to
realize the physical process responsible for the climatology of the
COSMIC-measured Es layer, we simulate the temporal and global distribution of
the occurrence of the Es layer in accordance with wind shear Theory. We
calculate vertical ion drift velocity based on empirical models of the ionosphere,
including HWM07, MSIS00, IGRF. The ferric ion (Fe+) density calculated from
Whole Atmosphere Community Climate Model(WACCM) is used to obtain ferric
ion vertical flux. The simulation results show that the seasonal asymmetry of
the Sporadic E layer occurrence rate between the summer and winter
hemispheres is very likely caused by the neutral wind shear in the Es region.
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