Variability of neutral temperature in the high-latitude upper atmosphere

The upper atmosphere at high latitudes is a region which is bombarded by electrons and protons, which are the source of the aurora, often seen as spectacular coloured and dynamic lights in the dark sky. The aurora over Svalbard (lat 78.2 N, lon 16.0 E) where our instruments are located, has special properties which make this an ideal place to study the upper atmosphere. The location is particularly important because it is dark during the daytime in the winter months, a special property of this most northerly site. The colour of the aurora, or wavelength of the light emitted, depends on both the energy of the incoming particles and how that energy is lost during the passage of the particles, and on the composition of the atmosphere that the particles travel through. As a result, optical measurements of specific wavelengths can provide detailed information about the atmosphere, and about the energy of the precipitating populations.

This project will use an advanced design spectrograph which makes measurements over a range of different wavelengths simultaneously. One emission is from excited oxygen ions O+, which is a signature of low energy electron precipitation (typically electrons with energies of about 100 eV) and has a peak brightness at around 300 km in height. We have discovered recently (Whiter et al Ap.J 2014) that the processes that produce the O+ ion in aurora have some special properties, and as a result the emission can be used to obtain the temperature of the O atoms in the region where they emit. This temperature is known as the neutral temperature, which in the auroral region has not been easy to measure so far; this project provides an exciting new method to quantify the changes that occur during auroral energy input, and to compare these changes to modelling studies and also to existing empirical models, which are known to have large uncertainties. The neutral temperature is an important parameter for studying changes on more global scales, and although our studies are from one specific location, the data we are using has been continuous during the dark hours since 2003.

Another emission that we measure is from hydroxyl molecules which are excited by ultra violet radiation. The emission is known as airglow, and is from a region around 85-90 km in height, known as the mesopause. Precise measurements of these emissions can be used to obtain the temperature of the atmosphere at these heights. Consequently, we can add these observations to those described above (from around 300 km) to determine if there are any correlations, and then try to understand what the mechanisms may be.
Moving a little higher up in the atmosphere, one of the strongest emissions is from molecular nitrogen, which has a peak emission height of between 100-150 km. We have developed a "synthetic spectrum" of the emission, which is a theoretical solution of the shape of the emission spectrum. This shape is dependent on the temperature of the molecules, and so we can make a best fit of the measured spectrum to the theoretical, in order to estimate the neutral temperature at the height of the emission. In combination we therefore have the possibility of measuring the neutral temperature at three distinct heights, depending on the auroral conditions.

Finally we will make use of very high resolution auroral cameras which we operate in the arctic close to the spectrograph. The ASK (Auroral Structure and Kinetics) cameras provide high time and spatial resolution (1/32 s and 10 m) images of the aurora in a frame approximately 5x5 km (at 100 km altitude). ASK consists of three cameras which provide the same image at different wavelengths which, in combination with modelling, are used to find the energy input within the auroral structure. The spatial and temporal variability of precipitating charged particles is at the heart of the physics of the behaviour of the polar upper atmosphere.

The research proposed here will have societal impact in three main areas: outreach, space weather applications, and contribution to skills required by the economy. Here we provide a summary of the impact expected; the avenues by which we 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 the award of funding (contingent on support for ASK) of an Aurora Zoo will provide an excellent vehicle to engage interested members of the public, allowing them to view our data and take part in our science. The aurora is one of the most exciting natural phenomena, and the images obtained from our cameras are a great draw at talks to the general public and at schools.

Real-time monitoring of the upper atmosphere
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The PI has developed a fast and automatic method for extracting emission components from measured HiTIES spectra. The additional software components for deriving neutral temperatures from the measurements which will be developed during this project are also expected to be fast and automatic, and therefore will be excellent for producing temperature estimates in real-time. We will develop a prototype, publicly accessible service for distributing neutral temperature measurements over Svalbard in real-time. These are expected to have a range of applications, such as in space weather monitoring and public outreach. The successful demonstration of the prototype service would then be used as the basis of a proposal for the capital and ongoing expenditure which would be required to provide this service on a routine basis (upgrade of IT and internet connectivity; annual maintenance and calibration visits).

Contribution to skills required by the economy
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An equally strong claim of benefit to the wider community is through the training of the scientists of the future, and other workers with scientific skills. If funded, this proposal will employ a PDRA. The training and career development of that researcher will be an integral part of the project, such that whatever the PDRA's long term employment (be that in academia, the private sector or elsewhere), the scientific skills developed through this research programme will make an important contribution to that organisation and the wider economy. This is highlighted by the range of employment destinations of past members of the Space Environment Physics group at Southampton (including BAE Systems, the Met Office, a partner in a European firm of patent attorneys, a consultant in climate change at Environmental Resources Management, researchers in universities and research establishments [e.g. at Diamond], and an IT service delivery manager). The Aurora Zoo seed funding provided under the Pathways to Impact of Prof Lanchester's previous NERC grant allowed us to hire two summer students to develop the citizen science project. In doing so, they had direct advice from the Zooniverse team and became equipped with specific and desirable skills, which led to one taking up a position in a software development company. The breadth of these destinations shows that we can succeed in providing expertise across many boundaries.