Explore the fine structure of the polar coronal holes and find clues whether or not there are signatures of a local dynamo besides the global dynamo there. Tsuneta et al. (2008, ApJ 688, 1374) using Hinode/SOT found many strong (1 kG) magnetic concentrations with vertically oriented fields, which were fanning out with height, and ubiquitous transient horizontal fields in between. The 1-kG patches were coherently unipolar and their polarity was consistent with the dominant magnetic polarity of the polar region. Their size showed a tendency to increase with latitude. The lifetime of these kG patches (5-15 hr) was found to be longer than that of magnetic concentrations in the quiet sun. Dacie et al. (2016, A&A, 596, A69; 2017, A&A 606, A34) showed that the magnetic field distribution, as represented by the slope of a power-law, evolves in active regions from their emergence through the decay phase ending in a quiet-sun state in such way, which is consistent with magnetic flux being reprocessed by (super)granular convective cells. The reprocessing is breaking down larger flux concentrations, making the negative power-law slope steeper with time. Carrying out such analysis in polar coronal holes will reveal how different the magnetic fields in polar areas are from lower-latitude quiet-sun and coronal-hole areas, in particular concerning the importance of magnetic field reprocessing by convective flows, an important element of the local dynamo.
The particular magnetic field distribution in polar coronal holes implies that there should be difference in the behavior and activity in the atmosphere from those of the lower-latitude regions. Harra et al. (2015, Solar Phys., 290, 3203) carried out a long term study of polar regions with Hinode EIS and SDO AIA and found that the coronal non-thermal velocities measured in the polar region remained unchanged during the cycle, which was interpreted as a local dynamo effect. The number of bright points also remained unchanged. However there was an indication that the quiet intensity shows some increase. The polar view achieved by Orbiter will allow the physical characteristics of this region to be measured. The SOOP R_SMALL_HRES_MCAD_Polar-Observations should be adequate for these needs.
Other sub-objectives include:
4.5.1 Explore the quasi-biennial modulation of galactic cosmic rays (Laurenza et al., 2012) and of flare-CME onset (Telloni et al., 2015).
4.5.2 Explore the effect of the solar polarity reversal (Gnevyshev gap) on the heliosphere during solar cycle 25 (Storini et al., 2003) and compare with that of previous cycles.
4.5.3 Explore the possible effect of the Centennial Gleissberg Cycle on the heliosphere during solar cycles 24 and 25 (Feynman & Ruzmaikin, 2014).
4.5.4 Determine the solar wind, magnetic field, energetic particles and radio emission properties during solar cycle 25 and compare to those found by Helios.