How does the aurora heat the upper atmosphere?

My research will study the aurora, a beautiful display caused by energetic particles from space hitting the Earth's atmosphere at about 40 million mph. The aurora typically deposits 50 GW of power into the atmosphere, comparable to the electricity consumption of the UK. This huge energy source has considerable influence on the temperature and composition of the upper atmosphere, particularly in polar regions. The aurora is therefore one of many ingredients needed for computer simulations of the whole atmosphere, which predict changes to Earth's climate and to concentrations of gases such as ozone.

Intense currents flow within and around aurora, heating the atmosphere just as an electric current heats a resistor. This heating has dramatic effects on the upper atmosphere, but several fundamental aspects remain undetermined. Previously it has been very difficult to measure the temperature of the atmosphere at auroral heights; it is too high for weather balloons, but too low for spacecraft. However, I recently made the exciting discovery, through experiment and theory, that the ratio of brightnesses of two specific auroral colours depends on the temperature of the atmosphere; therefore by observing these wavelengths in the aurora we can calculate the temperature. My idea is to use extremely sensitive cameras equipped with colour filters to make maps of atmospheric temperature, just like a thermal imaging camera. These temperature maps can be combined with radar measurements of the upper atmosphere to estimate the electrical conductivity, which is an important property influencing the flow of electric current through near-Earth space and the atmosphere. A computer simulation will help me to understand how different types of aurora are produced, what electric currents they generate, and how the aurora affects the temperature and chemistry of the upper atmosphere.

My research will have societal impact in three main areas: outreach, improvements to atmospheric modelling, and predictions of orbital decay. Here I provide a summary of the impact expected; the avenues by which I will achieve this impact are outlined in the Pathways to Impact document.

Outreach
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The aurora has great appeal as an outreach topic, and a citizen science project called Aurora Zoo will provide an excellent vehicle to engage interested members of the public, allowing them to view data and take part in my science. The aurora is one of the most exciting natural phenomena, and the images obtained from the Southampton cameras are a great draw at talks to the general public and at schools.

Improvements to atmospheric models
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I have designed novel observation techniques which will produce a new, powerful data set for understanding how the aurora affects the upper atmosphere. The results of this research (e.g. variations in neutral temperatures) will lead to improvements in atmospheric and climate models used to inform policy decisions, with associated benefits to society over the medium and long term.

Orbit Decay
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My research into the variable auroral atmosphere will lead to improvements in predictions of atmospheric drag on space debris and spacecraft in low Earth orbit. These improved predictions will benefit commercial and governmental operators of spacecraft, both through improved quantification of risk associated with space debris, and by overcoming challenges associated with operating spacecraft at very low altitude. They will also benefit national and international agencies concerned with space policy and with tracking space debris in order to mitigate risks to spacecraft and astronauts.