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Solar Wind and CMEs
Eruptions on the Sun's surface occur often. During normal solar activity the intense heat of the corona of about 1,000,000°C (1,800,000°F) to 2,000,000°C (3,600,000°F) accelerates the plasma to escape velocity. A million tons of matter are hurled into space every second at an average speed of 400 km/s (900,000 miles/hr). Extreme speeds vary from 300 km/s (700,000 miles/hr) to 900 km/s (2 million miles/hr). In the process the plasma drags the magnetic field lines of the Sun out into space. A million tons of matter per second is huge. However, since this solar wind is spread throughout space in all directions, there are only about 6 protons per cubic centimeter when the solar wind reaches Earth. The Ulysses spacecraft and the Advanced Composition Explorer (ACE) have gathered considerable information about the solar wind. Would you like to know the solar wind conditions for the past seven days?
Solar winds are comparable to daily breezes on Earth -mild and steady. Solar flares, however, are like intense storms. The solar flares are much more powerful than solar winds, but they are localized and tend to blast material in just one direction. Flares release a quick burst of energy equivalent to 10 million volcanic eruptions or more than a billion hydrogen bombs. A coronal mass ejection (CME) is the like a hurricane- an energetic storm spread over a large area. A CME is the eruption of a huge bubble of plasma from the corona. A CME travels between 400 km/s (1 million miles per hour) and 1000 km/s (5 million miles per hour). A typical eruption can carry a billion tons of plasma, a mass equal to that of 10,000 aircraft carriers. A CME is very directional, blasting material out in a fairly narrow jet that can expand to about 30 million miles.
These are frames from an animation of a CME (27 megabyte file). Courtesy of SOHO/LASCO consortium. SOHO is a project of internatinonal cooperation between ESA and NASA.
Coronal mass ejections occur only about twice a week when sunspots are at a minimum. However, they occur as often as 4 to 5 times a day when sunspot activity reaches its maximum. CMEs are randomly distributed across the surface of the Sun. Therefore, very few are aimed at Earth. Most of the energy of a CME that does arrive at Earth is deflected by The Earth's Magnetosphere. The energy from a CME directed at Earth can create auroras, damage satellites, disrupt radio communication, burn out power transformers and corrode pipelines. On the relatively unprotected surface of the Moon, these high-energy protons could easily kill a human. CMEs that are directed at Earth can affect the instruments of satellites, causing temporary instrument malfunctions and computer shutdowns. In a few instances satellites were disabled. To observe the CMEs directed at the Earth in more detail, the STEREO (Solar Terrestrial Relations Observatory) mission is planned for launch in 2005. It will observe CMEs directed at the Earth by placing two spacecraft in a solar orbit identical to Earth's orbit. One spacecraft will precede the Earth and the other will follow. Coronal mass ejections aimed at the Earth will be measured in stereo revealing unprecedented three-dimensional structures of the CME.
- NASA Official: Dr. James Thieman
- Project Manager: Don Robinson-Boonstra
- Website Manager: Bryan Stephenson