Neutral Temperature Changes in Fine Scale Aurora

The aurora is a significant source of heat in the high latitude upper atmosphere: tens of gigawatts of energy from the solar wind is deposited as heat in the thermosphere and ionopshere (Østgaard et al 2002). Strong electric fields and currents associated with the aurora cause heating through friction between ions and neutrals (Joule heating) and resistive heating by magnetic field-aligned currents (Lanchester et al 2002). This energy input must be included in whole-climate models and models used to predict additional drag on spacecraft and space debris in Low Earth Orbit during geomagnetic storms. We present results from a new technique to measure neutral temperatures in fine-scale aurora at high spatial and temporal resolution (tens of milliseconds) using simultaneous images of emissions in two different parts of the auroral molecular nitrogen spectrum from the University of Southampton’s Auroral Structure and Kinetics (ASK) multi-spectral imager. The technique measures the neutral temperature at the altitude of the auroral emissions so the observations require careful interpretation to separate local neutral temperature changes from spatial variation in auroral altitude across each image. Height profiles of the neutral temperature are therefore obtained using a third image in an atomic oxygen emission to determine the energy of the auroral electron precipitation and hence estimate the altitude of the aurora and temperature measurement. The resulting profiles show rapid neutral temperature changes on the order of several hundred Kelvin across E-region altitudes (between 100 km and 160 km). The coolest temperatures are found within the brightest regions of the aurora, whereas higher temperatures are typically associated with the edges of arcs where the electric field is expected to be strongest. The neutral temperature profiles are compared to ion temperature profiles from the European Incoherant Scatter (EISCAT) Svalbard radar (co-located with ASK) to better understand Joule heating and ion-neutral coupling in the extreme electrodynamic environment surrounding the aurora.