ACE and Space Weather

The Sun's activity causes large changes in the Sun's plasma and energetic particle populations, and these changes are responsible for the "space weather" that affects Earth. Space weather can impact the upper atmosphere and may influence long-term climate trends. The effects are related to coronal mass ejections (CME), solar energetic particles (SEP), and coronal holes, the source of high-speed streams. The largest storms occur when a fast CME hits Earth shortly after its shock arrives.

Geomagnetic storms (magnetic storms on Earth due to solar activity) produce the Aurora borealis and Aurora australis - the Northern and Southern lights and can also cause a variety undesirable consequences. Electrical current surges in power lines, interference in the broadcast of radio, television, and telephone signals, and problems with defense communications are all associated with magnetic storms. Odd behavior in air and marine navigation instruments has been observed, and a compass anywhere on Earth is certainly affected. These storms are known to alter the atmospheric ozone layer. Even increased pipeline corrosion has been attributed to them.

Major solar activity is a very serious concern in space flight. Communications may be disrupted. Large solar disturbances heat the upper atmosphere, causing it to expand and create increased drag on spacecraft in low orbits, shortening their orbital life-time. Spacecraft could potentially tumble and burn up in the atmosphere. Intense SEP events contain very high levels of radiation, more than a million times the normal daily dose of a human on Earth. Radiation sickness can result when humans are outside the pro-tective magnetosphere of the Earth, as in missions to the moon and to Mars.

High-energy solar protons can produce increased radiation in the atmosphere at altitudes where super-sonic aircraft fly. This is especially true for flights over the north and south magnetic poles, areas unprotected by the Earth's magnetic field, where the radiation has direct access to the atmosphere. To reduce the risk to aircraft crews and passengers, and reduce risk to the aircraft, routine forecasts and alerts are sent through the Federal Aviation Administration so that a flight in potential danger can consider what course of action to take to minimize radiation exposure. The National Oceanic and Atmospheric Administration (NOAA) forecasts high-speed solar wind and solar particle events.

The continuous broadcast of solar wind, magnetic field, and SEP data from ACE is expected to allow very accurate forecasts of major activity up to one hour beforehand. In particular; ACE will detect large CMEs and their associated shocks before they reach Earth, just like weather stations on Earth measure major storms as they move across the continent. This will remove much of the guesswork from space weather forecasts and should represent a major advance in NOAAs forecast ability, as well as furthering our understanding of the scientific processes involved.