Saturday, March 03, 2007

Heliophysics:The New Science of the Sun-Solar System Connection

A year of scientific collaboration and public engagement events aimed at understanding space weather and the Sun's true effects throughout the Solar System starts today. The International Heliophysical Year (IHY) will begin with a ceremony held at the United Nations Science and Technology Subcommittee Session in Vienna on 19 February 2007.

The Sun connects with all the planets via the solar wind, a flow of electrically charged particles that constantly 'blows' off the Sun and creates 'space weather'. Space weather interactions can affect and erode the atmospheres of Earth and other planets, and, when channelled through a planetary magnetic field, create beautiful aurorae. Until now, physicists have been principally concerned with the way the solar wind interacts with Earth, the so-called Sun-Earth connection. Now it is time to think bigger.

"When people hear the word astronomy, I believe only five percent think of the Sun-Earth connection. Through IHY, I would like to raise that to at least ten percent," says Carine Briand, Observatoire de Paris à Meudon, and the co-chair of the European coordinating committee for IHY.

Powerful events such as the 2003 Halloween space storms obviously affect astronauts, satellites, communication and electrical power systems. But it may seem that the space environment is usually benign and unimportant because such storms are rare. In fact, the constant variation of the space environment makes the time between storms anything but calm.

Magnetic active regions on the Sun emerge and decay over days to weeks. The numbers of active regions varies regularly with the 11-year solar cycle and erratically over longer time scales - up to centuries. The patchy distribution of regions over the Sun produces variation at the 27-day solar rotation period. Many phenomena – emission of visible light, intensity of short wavelength radiation, solar wind characteristics, and blocking of galactic cosmic rays – vary significantly with the time scales of the solar magnetism, even without storms.

Light from the solar surface directly heats the Earth’s surface and lower atmosphere. Dark sunspots and bright faculae in magnetic regions alter the emission of light from the surface enough to affect the climate over long intervals.The corona above magnetic regions is heated to millions of degrees and emits strong and variable amounts of X-rays, EUV, and UV radiation. The radiation heats, dissociates, and ionizes the atmospheres of Earth and other planets, producing our ozone layer the ionosphere,and thethermosphere.It alters atmospheric chemistry and temperature, which in turn modifi es the mixing of molecules over height andlatitude. As these layers heat and cool, they become more and less dense, changing the drag that slows satellites until they reenter.

The solar wind, striking Earth’s magnetic field, drives the acceleration of energetic particles that fill the radiation belts. By contrast,Mars has no global magnetic field, and the solar wind directly impacts and strips away Mars’ upper atmosphere. The wind’s magnetic field,constantly reshaped by change on the Sun even in absence of solar events, can power intense geomagnetic storms, with the whole array of energetic particle acceleration, aurora, and disturbances of satellites systems.Coronal holes above stable solar areas power the solar wind, whichcarries magnetic fields with it. The magnetized solar wind, filling the heliosphere, deflects many of the cosmic ray particles that fill the rest of the galaxy.

Nasa Heliophsics the new science


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