Representation of the Weddell Sea Anomaly obtained by the Swarm constellation

Abstract:

Recently it has become apparent that the Weddell Sea Anomaly (WSA) and the mid-latitude nighttime summer anomaly (MSNA) are phenomena, which are governed by similar mechanisms. Key questions relate to the fact how do those anomalies set up or how does spatial and altitudinal structure evolve. In-situ registrations of electron density from the Langmuir probe onboard three Swarm satellites are used to study the spatial and temporal evolution of nighttime plasma density enhancements. The study introduces the normalized density difference index $I_{NDD}$ to provide global estimates of the phenomenon. The advantage of the index is, that it provides relative values and can be used for further comparison with external missions and exhisting ionospheric models (like IRI). With proposed index, we find signatures the Weddell Sea Anomaly and mid-latitude nighttime summer anomaly in the ionosphere. The study provides evidence that occurrence of the WSA and MSNA is not limited to the local summer conditions but tends to occur in remaining seasons. Analyzed annual trends and spatial pattern of $I_{NDD}$ suggest that observed anomalies evince similarity with the behaviour of the equatorial ionosphere.
Multi-instrumental analysis based on the Swarm data provide better insight into the WSA phenomenon and should help to acquire full understanding of responsible processes.