The solar wind is a gas plasma blown off the surface of our sun at a million miles per hour. It is the outer atmosphere of the sun expanding out into space in all directions all the time. It effectively forms a shield around our solar system like a bubble that is called the heliosphere that tends to reflect harmful cosmic rays originating from other star systems, basically pushing away the rest of the galaxy from our solar system. This outward flow of particles is constant and creates outbound pressure referred to as a wind, a solar wind.

Sometimes it is stronger than at other times. Apparently, it is also sometimes weaker, as new data suggest.


An image of the sun taken Sept 25 using the SOHO observatory’s Extreme ultraviolet Imaging Telescope at 304 Angstrom. SOHO, NASA/ESA

This is perplexing. The strength of the wind forms a pressure barrier that repels the intergalactic cosmic radiation, which is quite harmful to life, especially life floating around in space, space stations and spacecraft. Earth is protected by its magnetosphere and by its atmosphere for two additional tiers of protection. Spacecraft orbiting the Earth would also be protected by its magnetosphere. Spacecraft en route to the moon would have minimal protection.

The spacecraft Ulysses launched in October 1990, is a mission out of the plane of the planets orbiting the polar regions of the sun. Ulysses has detected a gradual decrease in the solar wind over the last 15 years equal to nearly 25%.

A segment today on Science Friday, talks to David McComas, Principal Investigator for Solar Wind Observations over the Poles of the Sun (SWOOPS) Experiment, about the solar wind and the findings by the spacecraft Ulysses. The archived podcast should be available later today here.

The Ulyssess/SWOOPS web site is here: .

The spacecraft Ulysses is flying over the Sun’s north pole just as a new solar sun cycle is beginning. The flyby began November 2007 and will continue through March 2008. Ulysses was launched in October 1990 from the space shuttle Discovery. Previous flybys of the Sun’s poles occurred in 1994-95, 2000-01 and 2007.

Solar wind speed vs latitude When sunspots break up, their magnetic fields decay and get carried towards the poles by action of vasts seas of plasma, making the poles a “graveyard for sunspots”. The older magnetic fields fall under the polar surface down to the sun’s inner magnetic dynamo, about 124,000 miles down (200,000km). Once there, the solar dynamo action amplifies the magnetic fields which again become used in future solar cycles, a sort of recycling effect.

On previous flybys of the solar poles, the magnetic north pole during the previous solar cycle was 8% cooler than the south pole, or about 80,000 degrees cooler. The current flyby will allow detailed comparisons to be made of the north and south polar temperatures with virtually no gap in time during the measurements.

Ulysses also discovered a high speed polar wind where the magnetic field opens up and allows pieces of the solar atmosphere to stream out at a million miles per hour. This is shown in the “clock plot” graphic above of solar wind vs. latitude. By constant monitoring of the Sun over all latitudes, Ulysses has found the Sun behaving a bit odd. The solar wind appears to be confined to latitudes above 45 degrees whereas in the previous solar cycle, the solar wind reached all the way down to the Sun’s equator.

Solar data

So what’s going on here? The Ulysses flybys hope to determine what the meaning of this is. Is it something to be concerned about in the future? The solar wind has a direct effect on Earth and Earth’s magnetic field. Data on recent solar cycles are in the graphic above and is available as a pdf file at either NASA link below. Solar activity and sunspots are driven by the solar magnetic field which changes over its 22 year cycle period. During the first flyby, the Sun’s magnetic pole in the north was positive with outward facing fields and negative at the south pole with inward facing fields. During the second orbit at sunspot maximum the poles ‘flipped’ to their opposites; negative at the north pole and positive at the south pole. The polar fields are now 50% of the strength they were during the first flyby.

The Sun is a fascinating object and more data should be available later in the year.

Graphics are from NASA.

For further information: and .