Connecting the Evolution of Polar Coronal Holes to the Heliosphere
Abstract
Polar coronal holes are regularly observed capping the northern and southern solar poles in EUV images of the corona and are understood as the primary source of the fast solar wind. Polar holes are also the longest-lived solar magnetic features and observed to have strong solar cycle dependence - becoming more stable and prominent in solar minimum and disappearing at solar maximum. We make measurements of these features from 1996 through 2015 using four different NASA imagers: SOHO EIT, STEREO A and B EUVI, and SDO AIA. This dataset reveals several long-term trends in the corona. A measurement of the axial symmetry of the polar holes is seen to have clear solar cycle dependence. Polar coronal holes are aligned with the solar rotation axis during minimum and have a maximum off-axial perturbation of about 8 degrees in the declining phase of the solar cycle. With nearly 20 years of coronal hole measurements, we are able correlate the evolution of the polar holes to complementary measurements of the solar wind.
- Publication:
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Solar Heliospheric and INterplanetary Environment (SHINE 2015)
- Pub Date:
- July 2015
- Bibcode:
- 2015shin.confE.123K