Results from the SPIDER sounding rocket: multi-point in-situ measurements in the auroral E region

The SPIDER sounding rocket was launched on February 2^nd, 2016 from Esrange in northern Sweden, releasing ten Free Falling Units (FFUs) in the ionospheric E region (100 to 120 km). Each FFUs was equipped with four spherical electric field probes and four spherical Langmuir probes respectively deployed on 2 and 1-meter long wire booms and a 3-axis fluxgate magnetometer. This suite of instruments was designed to probe the electric and magnetic field vectors, as well as the plasma density and temperature inside the auroral electrojet. One of the project's main scientific objective was to observe Farley-Buneman instability which is excited by the relative drift between the electrons and ions at these heights, but providing multi-point measurements also aimed at characterizing electrostatic waves on various spatial scales.

Although only six FFUs were successfully recovered after landing, the recorded data presents interesting results, which will be discussed in detailed during this presentation.

The electron density and temperatures were successfully retrieved from the Langmuir probes for two FFUs. A similar large-scale structure of the aurora was observed independently by the incoherent scatter radar measurements from the EISCAT facility. The current collected by the Langmuir probe sweeps was also reproduced by simulating the plasma environment around the FFU using SPIS, thus confirming the analytical theory used in the analysis. Local disturbances in the plasma were observed simultaneously between the two FFUs along their respective trajectory, and both FFUs revealed detailed layer structures in the aurora.

The electric field vector was successfully retrieved in the North-East coordinate system for three FFUs using a novel GPS-based attitude reconstruction method. The direction of the large-scale electric field vector was similar for all three FFUs, and its temporal variation was compared to the aurora motion recorded by the ground-based ALIS multi-camera system. The high-temporal resolution of the electric field measurements also allowed for resolving spatial scales down to meters, but no significant spectral power was observed in the range where Farley-Buneman instability was expected.

A re-flight of the experiment is planned for early 2020, and the improvements of the FFU system are also briefly presented.