| dc.description.abstract | Ionosphere irregularities have been studied by using ionosondes, VHF radars, airglow images and satelites for several years. In the article, F region plasama irregularities are observed with the VHF radars, the Chung-Li Lunping ionosonde, the Yonaguni airglow image, and the Formosat-3 (COSMIC) satellite. By using the different instruments, the relation of the plasma distubulences detected can be studied at the different scales. The coordinated observation of the F region irregularities associated with the medium scale travelling ionospheric disturbances (MSTIDs) shows that the radar echoes are located at the west edge of the depletion zones of the 630 nm airglow image. The bulk echo structures of the 3-m field aligned irregularities (FAIs) drifted eastward at a mean trace velocity of about 30 m/s that is in general agreement with the zonal trace velocity of the MSTIDs shown in the 630 nm airglow images. These results suggest that the observed F region 3-m FAIs for the present case can be regarded as the targets that are frozen in the local region of the MSTIDs. In addition, the radar-observed 3-m FAI echo intensity and spectral width bear high correlations to the percentage variations of the 630 nm emission intensity. By using the VHF radars in Taoyuan, Taitung and Pingtung, three-meter field-aligned irregularities (FAIs) occurred in nighttime F region over Taiwan. Interferometry measurements show that the plasma structures of the observed 3-m FAIs occurred in a height range of 250-350 km are in a in a clumpy shape. The mean spectral width of the radar echoes is about 30 m/s and the Doppler velocity of the radar echoes is about 40 m/s toward (away from) the radar station. Comparing the VHF radar and the ionosonde ehoes, the studies show that in the beginning of the plasma disturbulences, the maximum frequency on the ionogram increases with the spectral width of the VHF radar echoes. The height of the spread F is associated with height of the 3-m FAIs. The reflection signals are seen on ionograms when spectral widths of the radar echoes are small. The plausible causes of these results are analyzed and investigated in this article. | en_US |