Equatorial Post-Sunset Plasma Irregularities As Seen from the Swarm Constellation Mission

Abstract:

Equatorial plasma irregularities are highly dynamic features in the post-sunset ionosphere. They include a modulation of many different ionospheric parameters at the same time, such as plasma density, neutral density, electric field, and magnetic field (electric currents). Variations in plasma temperatures are also expected. So far, these parameters have been sensed by different instruments deployed during different campaigns.

The newly launched satellite mission Swarm will provide observations of all these parameters onboard the same spacecraft simultaneously, with a sampling frequency of 1 Hz or higher. In addition, the Swarm constellation mission with 3 satellites, two flying side-by-side at about 470km altitude and with a local time difference of about 4min, and another satellite flying at 510km altitude provides excellent opportunity, e.g., to derive the spatial persistence of structures at different scales lengths.

This paper will show first results from Swarm satellite observations of post-sunset equatorial plasma irregularities. The occurrence frequency is compared to previously known results and with respect to expected variations in solar flux level and sensing altitude, correlation lengths for small and large scale structures are discussed and the simultaneous observations are used to estimate the drift speed and/or inclination of the irregularities. Given the actual state of the different Swarm data, it is tested whether and to which level irregularity magnetic signatures can be predicted by means of the remaining parameters that are sensed onboard the satellites.