Oscillations and Asymmetries in Polar Coronal Holes
Abstract
Coronal holes are the origin of the fast solar wind and define the quiescent heliosphere. Polar coronal holes are prevalent during solar minimum, non-axisymmetric, and are stable. They also offer an indirect measurement of the polar magnetic flux. Polar 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. We make new measurements of polar hole's perimeter and area in three EUV wavelengths between 1996 and 2017 using five different space-based imagers: SOHO EIT, STEREO A and B EUVI, PROBA2 SWAP, and SDO AIA. The generated time-series of coronal hole parameters have significant oscillatory power in them - however this produces a difficult data problem: multi-band, multi-instrument, heteroscedastic measurements with periodic signals. To separate the oscillations associated with physical phenomena from systematic measurement errors, we employ a generalized Lomb-Scargle periodic analysis. This technique allows us to simultaneously analyze the physical properties of polar coronal holes and identify regular periodicities in our data from other origins.
- Publication:
-
2018 Triennial Earth-Sun Summit (TESS)
- Pub Date:
- May 2018
- Bibcode:
- 2018tess.conf30921K