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Miruna Popescu, Armagh Observatory
"The Dark Side of the Sun: Myths and Facts about Coronal Holes, their Bright Events and the Fast Solar Wind"

Abstract:
The solar wind - a few million tonnes of charged particles that leave the Sun every second - is continuously flowing past our planet at huge speeds (equivalent to travelling from London to New York in 5-15 seconds). Sometimes the solar wind distorts the Earth's protective magnetic field, perturbing (and sometimes destroying) not just satellites but also terrestrial electronic systems, and creates the most amazing cosmic light displays in our atmosphere, namely the aurorae - also known as the 'northern lights' in this hemisphere. Strangely enough, the fastest and most steady streams of solar wind originate from coronal holes. These are the darkest and quietest regions of the solar atmosphere, and have the lowest magnetic activity. How such a large amount of matter escapes the Sun's huge gravity and reaches such high speeds (in the quietest solar regions!) is not yet known. In this talk I shall describe how our work on 10-year old data from a high-resolution solar spectrograph on the Solar and Heliospheric Observatory (SoHO) spacecraft has revealed that coronal holes are not as dark and quiet as they might seem. Rapidly evolving small-scale brightenings, some lasting as short as one minute, occur continuously inside coronal holes, heating plasma to high temperatures and accelerating it to high speeds. We are searching for the mechanism that generates such brightenings, as well as whether there is any connection between these brightenings and the origin and acceleration of the fast solar wind.

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Last Revised: 2007 January 31st
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