We investigate the evolution of eight well-observed persistent coronal holes (CHs) with life spans of 5--12 solar rotations, that were observed between 2010 and 2015. The aim is to increase our understanding of the evolution of CHs, as well as to investigate the basic physical mechanisms that govern the CH behaviour over its lifetime. Using combined AIA/SDO and HMI/SDO data, we derive several CH parameters such as area, intensity, and magnetic field characteristics as function of time. Using in-situ data from the ACE satellite located at L1, we study the corresponding solar wind plasma measurements. We find that 6 out of 8 CHs in our data set reveal a steady increase in the area followed by a decrease. For those we derive the average absolute change of area between two points in the growing phase with (10.2 +/- 3.5 )x 10^8 km^2 per day, while for the decaying phase it is (8.6 +/- 3.7)x 10^8 km^2 per day. We further found that the CH magnetic field strength is strongly related to the amount of area strong flux tubes contribute to the CH area. However, there is no correlation between the magnetic field and the total CH area itself, hence, the magnetic field variation follows a different evolutionary pattern. With the in-situ proton bulk speed, we derive for the growing area phase a strong correlation (Pearson cc=0.69) and for the decaying phase a moderate one (cc=0.45).
|Publication status||Submitted - 2021|