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Ann. Geophys., 21, 1039-1045, 2003
www.ann-geophys.net/21/1039/2003/
© European Geosciences Union 2003
The intermediate layers and associated tidal motions observed by a digisonde in the equatorial anomaly region
C.-C. Lee1, J.-Y. Liu1,2, C.-J. Pan1, and H.-H. Hsu1
1Institute of Space Science, National Central University, NO. 300, Jung-da Rd., Chung-Li 320, Taiwan
2Center for Space and Remote Sensing Research, National Central University, NO. 300, Jung-da Rd. Chung-Li 320, Taiwan
Abstract. This investigation
presents an initial attempt to analyze a full year of daily ionosonde
observations relevant to the determination of plasma densities, tidal
structures, and ion transports in the equatorial anomaly region of the lower
ionosphere. Particular focus is on the intermediate layers, their seasonal and
diurnal variations, and cause-effect relationships. The ionogram database was
recorded using a digisonde portable sounder (DPS) at National Central
University (NCU, 24 °58' N, 121°11' E) during 1996. Statistical results
indicate that the intermediate layers appear primarily during the daytime of
the spring/winter months. The monthly median height characteristics reveal that
the layers descend from high to low altitudes and different tidal motions
control the layers in different months. Generally, the semi-diurnal and
quarter-diurnal tides, which cause ionization convergence, are mainly in the
spring/winter and summer/autumn months, respectively. Variations in the
electron densities of the layers also indicate that the density increases could
result from a great number of molecular and metallic ions. Furthermore, a novel
approach to ionogram presentation is introduced to investigate the intermediate
layers. This approach allows the DPS to characterize the detailed daily
information of the intermediate layers.
Key words. Ionosphere (equatorial
ionosphere; ionosphere-atmosphere interactions; ionospheric irregularities)
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