9:15 AM - 9:30 AM
[PEM12-02] Long-term statistical analysis of ionospheric irregularities observed by the MU radar and Equatorial Atmosphere Radar
Keywords:MU radar, Equatorial Atmosphere Radar, ionosphere, plasma bubble, QP echoes, MSTID
Field-aligned irregularities (FAIs) have been studied with VHF radars for several decades in various locations. The MU radar in Japan and the Equatorial Atmosphere Radar (EAR) have been operated by RISH, Kyoto University since 1986 and 2001, respectively, and stored a plenty of FAI observation data.
We conducted statistical analyses of the long-term FAI observations observed by the MU radar and EAR.
From the MU radar observation, it was confirmed that the E-region FAI occurs mostly in summer and has little correlation with solar and geomagnetic activities, while the F-region FAI occurs mostly in summer and often in winter and has negative correlation with solar and geomagnetic activities.These findings are consistent with those of previous studies, and the observations support the proposed theories. From simultaneous observations of E- and F-region FAIs, an interesting correlation is found. On days when F-region FAIs were observed, E-region FAIs were always observed. On the other hand, on days when E-region FAIs were observed, there is no correlation with F-region FAI occurrence. It suggests that E-region FAIs are a kind of necessary condition for F-region fAI occurrence and supports the theory that sporadic-E layer is a driver of F-region irregularities via electromagnetic coupling along the geomagnetic field lines.
From the long-term EAR observations, it was confirmed that there are clear solar activity and seasonal dependences of FAI occurrences, which are thought to be related with equatorial plasma bubbles. During high solar activity period, FAIs frequently appeared in March/April and September/October at around 20-21LT. During low solar activity period, FAIs were active from May to August and appeared in later local time (01-02LT). The activity was relatively low from November to February. It is not clear why the asymmetry between June and December solstices appeared at the geographic equator.
We conducted statistical analyses of the long-term FAI observations observed by the MU radar and EAR.
From the MU radar observation, it was confirmed that the E-region FAI occurs mostly in summer and has little correlation with solar and geomagnetic activities, while the F-region FAI occurs mostly in summer and often in winter and has negative correlation with solar and geomagnetic activities.These findings are consistent with those of previous studies, and the observations support the proposed theories. From simultaneous observations of E- and F-region FAIs, an interesting correlation is found. On days when F-region FAIs were observed, E-region FAIs were always observed. On the other hand, on days when E-region FAIs were observed, there is no correlation with F-region FAI occurrence. It suggests that E-region FAIs are a kind of necessary condition for F-region fAI occurrence and supports the theory that sporadic-E layer is a driver of F-region irregularities via electromagnetic coupling along the geomagnetic field lines.
From the long-term EAR observations, it was confirmed that there are clear solar activity and seasonal dependences of FAI occurrences, which are thought to be related with equatorial plasma bubbles. During high solar activity period, FAIs frequently appeared in March/April and September/October at around 20-21LT. During low solar activity period, FAIs were active from May to August and appeared in later local time (01-02LT). The activity was relatively low from November to February. It is not clear why the asymmetry between June and December solstices appeared at the geographic equator.