CORONAL HOLES. “During the declining phase of solar cycles, the coronal holes extend to low latitudes sometimes even reaching the ecliptic plane. When the high-speed solar wind emanating from the coronal holes runs into the slower solar wind, the interaction leads to a compression of the plasma and magnetic fields, forming corotating interaction regions (CIR).”
https://link.springer.com/article/10.12942/lrsp-2007-1