Royal Observatory of Belgium - Meridian Room
Heating of the Atmosphere by Auroral Processes
- Dr. Daniel WHITER
- Dr. Joshua CHADNEY
The aurora can cause significant localised changes in the chemistry and climate of the neutral and ionised upper atmosphere. Electric currents associated with auroral features heat the atmosphere, and auroral particle precipitation ionises and excites the neutral species present. The aurora is often highly dynamic and structured on multiple scales, and thus the associated electric field is also variable on small spatial and temporal scales. Radar instruments can be used to estimate the electric field in the ionosphere, but since the amount of Joule heating scales with the square of the electric field, it is important to measure the electric field with as little averaging as possible; coarse radar measurements lead to an underestimation of the heating. The University of Southampton operates a suite of optical instruments on Svalbard in the high Arctic, including a multi-spectral imager (called ASK) and a high-resolution spectrograph (called HiTIES). Through a clever choice of filters, ASK can be used to estimate the energy and flux of auroral electron precipitation in its narrow field of view surrounding the magnetic zenith. By observing prompt and long-lived (5s lifetime) emissions simultaneously, ASK can also be used to measure plasma drifts in the ionosphere, and hence electric fields, at much higher resolution than is possible using existing radar instruments. By applying an advanced fitting algorithm to HiTIES spectra the neutral temperature can be retrieved at 3 altitudes simultaneously (~87 km, ~120 km, and ~250 km). As a side product, the technique gives the total precipitable water vapour in the column of atmosphere above the instrument. We have run numerous campaigns combining ASK and HiTIES observations with the EISCAT Svalbard Radar (ESR), giving access to height profiles of electron and ion densities and temperatures in the upper atmosphere. The EISCAT profiles can be inverted to obtain energy spectra of precipitating energetic particles, which are fed in to the Southampton ion-chemistry model. In such a way, the energy dissipation within specific fine-scale auroral events can be studied.