Ionisation reversed diurnal cycle is one of distinctive features of the Earth's ionosphere, which is characterised by higher values of ionospheric plasma density registered in the night-time than in the daytime. Two well known examples of this phenomenon are the Weddell Sea Anomaly (WSA) and the mid-latitude nighttime summer anomaly (MSNA).
The WSA is a mid-latitude F region ionosphere phenomena taking place over the regions west of the Antarctic Peninsula. Though the WSA was discovered more than 60 years ago, still its generation mechanism is not fully understood and its modelling remains a challenge. Initial discovery of the WSA relied on measurements from the ground network of ionosondes. Satellite observations revealed that peculiar feature of the ionosphere is not limited to the southern hemisphere only. Similar behaviour is also present in the northern hemisphere.
In situ registrations of electron density from the Langmuir probe on board three Swarm satellites are used to study spatial and temporal evolution of night-time plasma density enhancements (NPDEs). The study introduces the normalised density difference index I_NDD (Normalized Density Difference Index) in order to provide global estimates of the phenomenon. I_NDD is provided as a higher level product derived from Swarm data.
This project is funded by the ESA, Contract No. 4000112769/14/NL/FF/gp.