Statistical study of abnormal polarity and density of field-aligned currents events

By using high resolution magnetic field data from Swarm A and C satellites during years of 2015 and 2016, we have investigated the spatial and temporal distribution of field-aligned currents (FACs) in the dawn-dusk sector by differentiating their polarity and relative current density for the first time. The normal polarity events consist of the poleward part flowing into the ionosphere and the equatorward part flowing out of the ionosphere in the dawn sector, which is reversed in the dusk sector. They are traditional R1 and R2 FACs. The occurrence frequency of the normal polarity event is about 70%, and the occurrence frequency of events with R1 FACs stronger than R2 is about a fact of 3 similar to 5 larger than those with R1 FACs weaker than R2. The abnormal polarity events, which are opposite to the flow directions of traditional R1 and R2 FACs, are termed as R1* and R2* FACs. They account for about 30%, and the occurrence frequency of R1* R2* is about a fact of 1 5 similar to 2.5 larger than that R1*>R2*. The normal polarity events are associated with the southward IMF B-z, which have a strong correlation with the merging electric field, and the net current density increases with the merging electric field and ionospheric conductivity. The R1 < R2 substorm process. Since the abnormal events are usually observed during periods of northward IMF B-z the latitude of these events is about 4 degrees higher than those of normal events. In the northern hemisphere, the R1* >R2* events tend to occur when IMF B-y <0 in the dawn sector, and the dusk events mainly occur during the period of IMF B-y >0, while the R1* <R2* correspond to the opposite polarity of IMF B-y and the situation in the southern hemisphere is opposite to that in the northern hemisphere.