Longitudinal difference in total electron content over the East Asian region: Feature and explanation

The mechanism of the longitudinal difference of ionospheric electron density is in general attributed to the thermospheric wind effect modulated by the local geomagnetic declination. Although this mechanism is tested in many case studies, there are other possible factors such as solar activity and so on which still need further investigations. In this paper, TEC data from two Chinese GPS stations located at almost same geographic latitudes but with a wide longitude span (~38°) are used to study the morphological features of longitudinal differences under various geophysical conditions. A parameter Rew is defined as a normalized measure of the TEC difference between the two stations. All the observed temporal variations of Rew are analyzed statistically, with the results showing that negative east-west differences (Western TEC>Eastern TEC) in the noontime are pronounced during Day of Year (DoY) 90-270, while nighttime positive differences (Western TEC