Solar Effects on the Polar Atmosphere: The Role of Energetic Particle Precipitation

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• Dr Annika Seppälä, BAS
• Monday 14 February 2011, 14:15-15:15
• Unilever Lecture Theatre, Department of Chemistry.

If you have a question about this talk, please contact Dr Alex Archibald.

This presentation I will give an overview of what has recently been learned about the impact of Solar energetic particle precipitation on the polar stratosphere and mesosphere. I will discuss the further implications on troposphere via atmospheric coupling mechanisms and some of the open questions on this linkage.

A large solar disturbance such as a flare or a coronal mass ejection results in emission of high-energy protons and other ions from the Sun. If these particles reach the Earth they set off an event known as a Solar Proton Event. In addition to these events the Earth continuously undergoes precipitation of energetic charged particles (protons and electrons) originating from the near-earth space. The charged particles enter (i.e. precipitate into) the Earth’s atmosphere causing ionisation in the middle atmosphere. This effect is confined to the polar regions, where the particles are guided by the Earth’s magnetic field. In the atmosphere the enhanced ionisation leads to increased production of odd nitrogen (NOx) and odd hydrogen (HOx) both of which participate in catalytic reaction cycles decreasing the amount of ozone. HOx gases have a short chemical lifetime but the NOx gases are mainly destroyed by photodissociation. Hence during polar winter, when little or no sunlight is present, the NOx impact on the atmosphere can be long-lasting. For example, following a series of large solar storms in Oct-Nov 2003, a 60% ozone depletion in the Arctic upper stratosphere was observed a month after the storms.

In this talk I will show satellite based observations of the effects of solar storms and energetic particle precipitation on the chemical composition and dynamics of the polar middle atmosphere. In addition to observations, I will also present modelling results from a detailed ion and neutral chemistry model of the atmosphere. Recently, analysis of meteorological data has indicated that during the winter season the distribution of polar surface air temperatures shows variability depending on the level of NOx producing particle precipitation, so finally, I will discuss the long term effects of energetic particle precipitation on the atmosphere and the possible further implications to polar climate via atmospheric coupling processes.

This talk is part of the Centre for Atmospheric Science seminars, Chemistry Dept. series.

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