Coronal holes are cooler, less dense regions on the Sun with open magnetic fields allowing solar wind to escape.
Appearance: Visible as dark areas in UV and X-ray images.
Impact on Earth: Can cause geomagnetic storms, enhancing auroras but usually not significantly disruptive.
Observation: Monitored by NASA's Solar Dynamics Observatory (SDO).
Solar Cycle: More common during solar minimum, but can appear anytime; typically polar during solar max.
Duration and Size: Can persist for several solar rotations (27 days each) and be very large, e.g., 30 times Earth's size.
Importance: Crucial for space weather forecasting due to effects on Earth's magnetic environment.