Zonal Variation Features of Low-Latitude Ionospheric Electron Density Observed by Swarm Constellation

摘要

In order to investigate the features of the zonal direction variation of low-latitude ionospheric electron density (Ne) at the altitude above the ionospheric F2 peak, Ne measurements probed by the lower pair of Swarm constellation from 17 April 2014 to 31 December 2017 have been analyzed. We found that in most cases the zonal direction variation of low-latitude Ne over a zonal separation of about 150 km can be ignored during local daytime. However, during 19:00-04:00 LT, i.e., local night, significant zonal direction variations of low-latitude Ne were often observed (with the occurrence rate of 12.49%) over the zonal separation of about 150 km, which were primarily induced by the presence of equatorial plasma irregularities (EPIs). The annual occurrence rate of significant zonal direction variations of low-latitude Ne decreased with the decreased solar activity during 2014-2017. Our findings show that under high solar activity condition significant zonal variations of low-latitude Ne took place frequently at local night over a zonal separation of about 150 km because of the presence of EPIs, which means regional forecasting (namely, Ne measurements observed over one location is used to predict that over another nearby location) may be a futile endeavor at night during high solar activity years.