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NOx and HOx production by energetic electrons and impacts on polar stratospheric ozone (NOHO)

NERC funded project 2013-2016

People: John Plane (PI, Leeds), Wuhu Feng (Co-I, Leeds), Tamas Kovacs (Leeds), BAS PI (Lead): D Newnham, Co-I’s: M Clilverd & R Horne

Project Partners: Martyn Chipperfield (University of Leeds), Dr Dan Marsh (NCAR), Professor Craig Rodger (University of Otago), Dr Annika Seppälä and Dr Pekka Verronen (FMI)

Predicting future climate change is intimately linked to understanding what is happening to the climate system in the present, and in the recent past. Studies in the Polar Regions provide vital clues in our understanding of global climate, and early indications of changes arising from the coupling of natural processes, such as variability in the amount of energy from the Sun reaching the Earth, and man-made factors. For example, the polar winter provides the extreme cold, dark conditions in the atmosphere which, combined with chemicals released from man-made chlorofluorocarbon (CFC) gases, has led to destruction of the stratospheric ozone layer 18-25 km above the ground every spring-time since the 1980's. The Southern hemisphere ozone 'hole' is now linked to observed changes in surface temperature and sea-ice across Antarctica, decreased uptake of carbon dioxide by the Southern Ocean, and perturbations to the atmospheric circulation that can affect weather patterns as far away as the Northern hemisphere.

Recovery of the ozone layer is expected now that CFC's are banned by international protocols, but this may be delayed by other greenhouse gases we are releasing into the atmosphere and natural processes including changes in the Sun's output. Although the total amount of energy as sunlight changes by a small amount (~0.1%) over the typical 11-year solar cycle, the energetic electrons and protons streaming from the Sun changes dramatically on timescales from hours to years. These particles are guided by the Earth's magnetic field and can enter the upper atmosphere, most intensely over the Polar Regions. A visible effect is the aurora, but the particles can also significantly modify the chemistry of the atmosphere down to the stratospheric ozone layer. Powerful solar storms can also damage satellites and disrupt electrical power networks. However the mechanisms by which energetic electrons generated by the Sun enter the Earth's atmosphere, and the complex, interacting processes that affect stratospheric ozone are not well understood, which limits our ability to accurately predict future ozone changes and impacts on climate.

We propose answering major unresolved questions about the impact of energetic electrons on stratospheric ozone by making observations of the middle atmosphere from Halley station in Antarctica. This location is directly under the main region where energetic electrons enter the atmosphere, making it ideal to observe the resulting effects. We will install a state-of-the-art microwave radiometer there alongside other equipment run by BAS scientists. By analysing the microwaves naturally emitted by the atmosphere high above us we can work out how much ozone there is 30-90 km above the ground as well as measuring chemicals produced in the atmosphere by energetic electrons that affect ozone. We will make observations throughout two complete Antarctic years/winters (1/2013-2/2015) and interpret them with the help of data from spacecraft that orbit the Earth and measure the energetic electrons entering the atmosphere. We will use the Antarctic observations and develop computer-based models to better understand the impact of energetic electrons on the atmosphere. The ultimate goal is to further understanding of the processes that lead to climate variability in the Polar Regions and globally - highly relevant for UK environmental science and collaborative research at an international level in which BAS and Leeds play a key role.

Potential Impact

This research will have impact in several areas:

It will have educational benefits to the wider public who will acquire a better understanding of climate change because the proposal addresses natural variability due to solar processes affecting the atmosphere against which longer term anthropogenic trends need to be detected. The effect of solar variability on climate is an issue of public interest, as indicated by its frequent appearance on the BBC News website. The subject has fuelled poorly-informed debate on anthropogenic versus natural climate change and it is important for the scientific community to produce sound observational evidence upon which arguments can be based and the relative significance of solar versus anthropogenic influence on climate can be firmly quantified.

Improved knowledge arising from this research will benefit the Met Office who will be able to use the outputs in informing and formulating representations of stratospheric ozone both synoptically and climatologically. Their decision about whether to include assimilated ozone information in Numerical Weather Prediction - weather forecasting - and climate models requires an assessment of the impact of solar energetic particle precipitation on ozone. We will communicate our results to the Met Office and the wider community, establish the specific user requirements of the Met Office, and formulate ways of incorporating our results into their assessments, through a workshop at BAS.

Other users who could benefit from this project are: Developers of advanced instrumentation, in particular UK companies developing analytical spectroscopy and imaging tools for security, forensics, pharmaceutical, and other industrial applications, and satellite instrumentation groups including the NERC-supported Centre for Earth Observation Instrumentation. The academia-industry organisations involved could benefit from the development of methodologies & protocols, computer-based data analysis tools, semi-autonomous technologies, and experience of deploying equipment in harsh environments that will arise from this project. Observational data from the Antarctic will be applicable to calibration/validation of satellite instruments monitoring the atmosphere on NASA, European Space Agency, and EUMETSAT platforms.

The wider community of scientists and engineers in government, public sector establishments, and industry will be informed of the project outcomes through the BAS website, articles in trade journals and publicity at relevant exhibitions, user group meetings, and knowledge exchange events.