Embla: A new optical instrument to measure auroral precipitation, neutral temperature and electric fields at high resolution

We have constructed a new high-resolution auroral imager, called Embla, to simultaneously measure energy and flux of auroral precipitation, neutral temperature, and electric fields in fine scale aurora. Embla is designed primarily for studies of auroral electrodynamics, substorm onset, and neutral heating by aurora. The instrument has recently been installed at Skibotn, Norway, very close to the EISCAT_3D radar transmitter site, and we expect the combination of radar and optical observations to enable better measurements for our science than either instrument can provide alone.

Embla builds on work done using the Auroral Structure and Kinetics (ASK) instrument, which has been stationed at the EISCAT Svalbard Radar since 2007. Embla has a spatial resolution in the E-region of ~30 m and a planned temporal resolution of at least 32 frames per second, allowing us to resolve the fine-scale structure and rapid dynamics of auroral features. It consists of 4 co-aligned imagers with identical 9 degree fields of view centred on magnetic zenith. Each imager is equipped with a different narrow passband interference filter, targetting emissions in N₂ 1P (2 imagers), OI 777.4 nm, and O^{+ 2}P. The combination of N₂ 1P and OI 777.4 nm observations allows us to image the characteristic energy and flux of auroral electron precipitation. The O^{+ 2}P emission has a long lifetime of 5 s, providing a means to observe ion drift perpendicular to the magnetic field and therefore a way to determine ionospheric electric fields at very high cadence in localised regions around the aurora. Finally, by combining observations from two of the imagers in separate regions of the N₂ 1P band we can image the neutral temperature at the altitude of the auroral emission. The simultaneous measurement of these properties of the aurora and ionosphere will allow us to investigate auroral electrodynamics in detail.