Three meter field-aligned irregularities (3m FAIs) associated with medium-scale traveling ionospheric disturbances (MSTIDs) that occurred on 5 February 2008 were observed by using the Chung-Li 52MHz coherent scatter radar. Interferometry measurements show that the plasma structures responsible for the 3m FAI echoes are in a clumpy shape with a horizontal dimension of about 10-78km in a height range of 220-300km. In order to investigate the dynamic behaviors of the plasma irregularities at different scales in the bottomside of F region, the VHF radar echo structures from the 3m FAIs combined with the 630 nm airglow images provided by the Yonaguni all-sky imager are compared and analyzed. The results show that the radar echoes were located at the west edge of the depletion zones of the 630 nm airglow image of the MSTIDs. The bulk echo structures of the 3m FAIs drifted eastward at a mean trace velocity of about 30m/s that is in general agreement with the zonal trace velocity of the MSTIDs shown in the 630nm airglow images. These results suggest that the observed F region 3m FAIs for the present case can be regarded as the targets that are frozen in the local region of theMSTIDs. In addition, the radar-observed 3mFAI echo intensity and spectral width bear high correlations to the percentage variations of the 630nm emission intensity. These results seem to suggest that through the nonlinear turbulence cascade process, theMSTID-associated 3mFAIs are very likely generated from the kilometer-scale plasma irregularities with large amplitude excited by the gradient drift instability.
