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Long-term evolution of coronal holes and associated co-rotating interaction regions

Between 2010 and 2015 we investigate a sample of eight well- observed persistent coronal holes with life spans of 5--12 solar rotations. We aim to increase our understanding of the formation and evolution of CHs, as well as to investigate the basic physical mechanisms that govern the CH behaviour over its lifetime. By combining EUV filtergrams from AIA/SDO and line of sight magnetograms from HMI/SDO, we derive a set of coronal hole parameters including area, intensity, and magnetic field characteristics as function of time. Using in-situ data from ACE measured near L1, we study the corresponding solar wind plasma properties. We find, based on the evolutionary pattern of the CH area, that the evolution of CHs can be divided into two types, regular ones revealing a steady area increase followed by a decrease - and irregular ones with no obvious pattern in the area evolution. For the two evolutionary phases of regular type CHs we find differences in the correlation between area and the maximum in-situ measured proton bulk velocities of the associated high-speed streams. We derive a strong correlation in the growing (Pearson cc=0.72) and a moderate one in the decaying phase (Pearson cc=0.55). The CH area is strongly related to the number of (strong) flux tubes and the magnetic field strength of the CH with their percentual coverage of the CH area. This supports the previous findings of strong flux tubes being the key elements in governing the evolution of CHs.

coronal holes, stream interaction regions

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