IRIS Movie of the Day
At least once a week a movie of the Sun taken by NASA's Interface Region Imaging Spectrograph (IRIS) is posted by one of the scientists operating the instrument.
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10 Sep 2016
Intriguing Prominence Mass Flows
Credit: IRIS, LMSAL/NASA, Wei Liu
[Background]: Solar prominences are cool material located at elevated heights in the million-degree solar corona. They are called prominences when viewed as bright emission off-limb and called filaments when viewed as dark absorption against the bright solar disk. They are typically 100 times cooler, and at the same time, 100 times denser than the surrounding hot and tenuous coronal plasma. Why such extreme contrasts in temperature and density can co-exist for a long time (up to weeks) remains a mystery. The importance of solar prominences lies in the fact that they can become unstable and erupt, often as the cores of coronal mass ejections, which can have serious space-weather consequences. The formation of cool prominence material out of the hot corona can also provide important clues for understanding the fundamental problem why and how the corona is heated. [This movie], taken by IRIS at 2796 Angstrom on August 17, 2016, shows a prominence on the northwest limb of the Sun. There are very interesting dynamic flows, including several episodes of plume-like structures pushing upward and tumbling, especially in the lower middle portion where the IRIS slit scans through. These chaotic mass flows do not appear to follow the (invisible) magnetic field lines, in contrast with those nearly horizontal threads (exhibiting laminar flows) at the top of the prominence that do. This is possibly due to the large fraction of the prominence mass being cool, neutral atoms that are not "frozen onto" magnetic field lines (rather than hot, ionized plasmas that do) and/or due to dynamic phenomena such as magnetic reconnection that can drive high-speed mass flows. Another interesting feature is the dark void at the bottom of the prominence and to the left of the IRIS slit. This is potentially a candidate of the so-called prominence bubble, a possible indication of magnetic flux emerging from the solar interior pushing into the atmosphere.