Coupling Between Chromosphere and Corona: Why it Matters for the Solar Wind
Abstract
The solar wind is driven by energy input which must be deposited mainly in the corona. In some sense, therefore, the solar wind ``starts'' in the corona, and most solar wind models have their lower boundary here. However, the underlying chromosphere and transition region is not only a ``passive'' supplier of solar wind plasma. Energy must be supplied as well in the upper chromosphere and transition region to ionize and heat the outflowing gas from chromospheric to coronal temperatures. While this energy input is usually small compared to the energy deposited in the corona, it nevertheless can have a crucial influence on the solar wind because the amount of energy deposited in the transition region limits the mass flux of the wind. Using a higher-order (16-moment) fluid solar wind model that extends from the chromosphere to 1~AU, we find that when protons are heated in the corona they may quickly become collisionless so that the heat flux deviates strongly from classical heat conduction, making it difficult to transport sufficient amounts of energy downwards to the transition region. The problem is most acute in the rapidly expanding magnetic field of coronal holes, where we find that adding even a small energy input in the transition region therefore can increase the solar wind mass flux by a factor ten or more, and not doing so leads to a wind much faster than what is observed even in high-speed streams.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2001
- Bibcode:
- 2001AGUSM..SH21B02L
- Keywords:
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- 7509 Corona;
- 7546 Transition region;
- 7859 Transport processes