Coronal holes are regions where the corona is dark. These features were discovered when X-ray telescopes were first flown above the earth's atmosphere to reveal the structure of the corona across the solar disc. The high-speed solar wind is known to originate in coronal holes. Magnetic fields buckle releasing previously constrained hot material from the upper atmosphere of the Sun. As a result, hot gas streams out into the Solar System, impacting planets, moons, spacecraft, and making space a dangerous place for astronauts.
CMEs are more common but less intense than solar flares.
A daytime layer of the earth's ionosphere approximately 50 to 90 km in altitude. This is the lowest region of the ionosphere. The D Region is where most HF absorption occurs. A daytime layer of the earth's ionosphere roughly between the altitudes of 85 and 140 km. The upper layer of the ionosphere approximately 120 to 1500 km in altitude.