Characteristics of medium and small-scale ionospheric disturbances over Beijing

In this paper, characteristics of medium and small-scale ionospheric disturbances over Beijing were studied by ionosonde observation data. The cases of medium and small-scale ionospheric disturbances over Beijing on Nov. 13, 2017 were analyzed using the rapid-run observation data of the PDI ionosonde. The results show that the V-shaped (or U-shaped) descending structure in the ionograms is an "explicit" feature of the medium-scale ionospheric disturbance. On the other hand, the small-scale ionospheric disturbances mainly occur at lower altitudes. They are not accompanied by distinct anomalous structures in the ionograms. The characteristics of the occurrence rate of medium-scale ionospheric disturbances over Beijing were presented by statistically studying the abnormal trace events in ionograms from 2010 to 2021. The median-scale ionospheric disturbance characterized by these abnormal traces is a mainly daytime phenomenon. Its occurrence rate is significantly higher in winter than those in other seasons. Furthermore, the occurrence rate is higher under low solar activities, which shows an inverse correlation with solar activity. The correlation with geomagnetic activity is still unclear.