Reexamination of the Sq‐EEJ relationship based on extended magnetometer networks in the east Asian region

Abstract

We reexamined the daily Sq‐equatorial electrojet (EEJ) relationship based on these extended magnetometer networks in the east Asian region: (1) the Circum‐pan Pacific Magnetometer Network (CPMN), (2) the International Real‐time Magnetic Observatory Network (INTERMAGNET), and (3) the World Data Center for Geomagnetism, Kyoto (WDC). Daily variations of the geomagnetic field for geomagnetically quiet days (Kp ≤ 2+) from 1996 to 2005 were analyzed. Noontime eastward Sq current intensities were estimated by latitudinally integrating the north‐south component of the Sq field. The corresponding EEJ intensities were estimated from the daily geomagnetic field variations observed at Davao station (dip latitude of −0.84°deg). We discovered that these intensities of daily Sq and EEJ are well correlated on a long‐term basis (r = 0.80). The dependences on the solar activity (as indicated by F10.7) and season (the day number) of Sq and EEJ variations were examined. It was demonstrated that both daily Sq and EEJ intensities are correlated to F10.7 with similar sensitivities. F10.7 is known to show similar variations with solar EUV radiation which causes ionization and heating of the ionosphere. For seasonal dependence, both daily Sq and EEJ intensities show predominant semiannual variations with similar spring‐fall asymmetry. The effect of seasonal changes of the EUV flux into the low‐latitude ionosphere is considered. Our results indicate that the daily values of Sq and EEJ react, in the same manner, to temporal changes of solar ionization and heating of the ionosphere.