What is solar wind?

Our Sun is constantly emitting high-energy matter in the form of electrons, protons, and other particles. This "solar wind," as it is called, is largely deflected by the Earth's magnetic field, sometimes penetrating the upper atmosphere. While there is no scientific proof, some scientists believe that changes in the solar wind can have long-term effects on our planet's climate.

What is a geomagnetic storm?

A geomagnetic storm is the term used for a strong increase in solar wind activity— including intense X-rays—that affects the Earth's magnetic field.

What effect does solar activity have on life here on Earth?

By the time the solar wind reaches the distance of Earth's orbit, its density is only a handful of particles per cubic inch. Even so, it is enough to have caused substantial radiation damage to life on Earth over the several billion years of Earth's history, if not for Earth's protective magnetosphere.

When solar activity is particularly strong, such as during a solar flare, the stream of charged particles can increase dramatically. In that case, these ions can strike molecules in the upper atmosphere, causing them to glow. Those eerie, shimmering lights are called the Aurora Borealis (Northern Lights) and Aurora Australis (Southern Lights). During this time, Earth's magnetic field can temporarily weaken, causing our atmosphere to expand; this can affect the motion of satellites in high-Earth orbit. In extremely strong periods of solar flux, electrical power grids can be affected.

How fast does the solar wind travel?

The flow of plasma out from the Sun is generally continuous in all directions, typically moving at speeds of several hundred kilometers per second. It can, however, gust out of holes in the solar corona at 2,200,000 miles per hour (1,000 kilometers per second) or faster. As the solar wind travels farther from the Sun, it picks up speed, but it also rapidly loses density.

How far does the solar wind travel?

The Sun's corona extends millions of miles beyond the Sun's surface. The plasma of the solar wind, however, extends billions of miles farther—well beyond the orbit of Pluto. Beyond there, the plasma density continues to drop. There is a limit, called the heliopause, where the influence of the solar wind dwindles to just about nothing. The region inside the heliopause—which is thought to be some 8 to 14 billion miles (13 to 22 billion kilometers) from the Sun—is called the heliosphere.

How do sunspots affect weather?

While scientists still debate how important or significant sunspot activity is on our weather and climate, there are some theories. In the short term, solar flares and winds do not influence weather to any significant extent because the magnetosphere and upper atmosphere are more than capable of absorbing their energy. Over the long term, however, there could be consequences if the Sun experienced a prolonged or permanent change in activity.

Fluctuations in solar activity typically occur in the ultraviolet wavelengths, and UV radiation is known to affect the Earth's upper atmosphere. Astronomers and some meteorologists speculate that X-rays, too, resulting from sunspots and flares could, over time, change the amount of nitric oxide (NO) in the upper atmosphere, and this would have an effect on the ozone. Sunspot activity can result in more cosmic rays penetrating the atmosphere, which, in turn, spur on cloud formation and increase precipitation.

More recently, there have been theories that significant decreases in solar activity predict oncoming ice ages on our planet. For example, during the Little Ice Age that lasted from the fifteenth through the eighteenth centuries (a period including the Maunder Minimum), sunspot activity was at a low point. Other minimums (the Dalton Minimum [1790— 1820] and Spörer Minimum [1420-1530]) also coincide with colder weather.

A photo taken at the Dryden Flight Research Center in Edwards, California, took advantage of a smoky sky to reveal sun spots. (photo by Tom Tschida courtesy NASA)

A photo taken at the Dryden Flight Research Center in Edwards, California, took advantage of a smoky sky to reveal sun spots. (photo by Tom Tschida courtesy NASA)

What has recent sunspot activity been doing?

Sunspot activity during the dawning years of the twenty-first century has been a rollercoaster ride. In 2004, it was reported that there were more sunspots on the Sun than the Earth had seen in some 8,000 years. The next year, however, there was an abrupt drop-off in sunspot activity, a trend that has continued through 2008 and into 2009. In fact, during the last months of 2008, there were almost no sunspots at all.

Is it possible to forecast space weather?

By understanding past solar activity patterns and comparing them to current observations, astronomers can make some rough predictions about possible upcoming geomagnetic storms. This type of forecasting is important, so that warnings may be issued concerning dangers to orbiting satellites and other space missions, as well as the risks posed to electric power grids on Earth.

Who managed to calculate cosmic ray activity on Earth dating back over 11,000 years?

Sami Solanki (1958-), an astronomy professor at Germany's Max Planck Institute, developed a method for estimating solar ray activity dating back millennia. Solanki based his method on the knowledge that cosmic rays create chemical reactions in the atmosphere. One byproduct of these reactions is carbon-14, which then precipitates down onto the Earth's crust. Trees and other vegetation absorb this radioactive form of carbon; preserved vegetation that has been buried underground for centuries can be dug up and its composition analyzed. Radiation from sunspots actually decreases the production of carbon-14, and so when sunspot activity is high, there is less carbon-14 for trees to absorb. Using this information, Solanki discovered that there has been more sunspot activity since around 1930 than during any other period going back 8,000 years.

 
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