Study of generating mechanism of ionospheric field-aligned irregularities and E- and F-region coupling

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Polarization electric fields in mid- and low-latitude ionosphere propagate along the geomagnetic field with small attenuation. Close electromagnetic coupling processes are thus expected in the E-region and F-region owing to this effect. They are, however, difficult to be observed. In this project we studied the electrodynamic coupling processes by means of simultaneous observations of E- and F-region ionospheric irregularities along the same geomagnetic field.1.We conducted FERIX (F- and E-Region Ionospheric Coupling Study) in June-August 2004. The MU radar in Shigaraki observed the F-region irregularities while E-region irregularities along the same geomagnetic field were observed with LTPR (Lower Thermosphere Profiler Radar) located in Sakata, Yamagata. During the experiment, National Institute of Information and Communications Technology (NICT) operated FM-CW ionosondes in three locations in Tohoku including Sakata. Observations with atmospheric imagers and total-electron content (T … More EC) measurement with the GEONET GPS network were conducted as well. The results show that, when F-region irregularities were active, intense E-region irregularities appear at the field-associated region, and they moved westward with the same phase speed. F-region irregularities appeared at the depleted region of the GPS-TEC with middle-scale traveling ionospheric disturbances (MS-TID) patterns. It is possible that polarization electric fields in both regions resonant each other to develop the associated wavelike structures.2.We also compared low-latitude irregularity echoes from the equatorial atmosphere radar (EAR) in West Sumatra, Indonesia and behavior of the background ionosphere with the meridional ionosonde chain SEALION by NICT. We found that E-region irregularities were suppressed when the equatorial Spread-F (ESF) was onset. This behavior was explained by the control of E-region irregularities by the polarization electric field from the ESF event.3.From these results, we could successfully clarify the importance of E- and F-region coupling processes in understanding the mid- and low-latitude ionosphere. Less