The 11-year Solar Cycle

The Sun is a source of light and heat for life on Earth.  Like earth, the sun experiences storms which are important in shaping the environment we enjoy today.

Every 11 years the sun undergoes a ‘stormy’ period of activity called the “solar maximum”, followed by a period of quiet called the “solar minimum”. During the solar maximum there are many

  • sunspots,
  • solar flares, and
  • coronal mass ejections (CME’s),

all of which can affect communications and weather here on Earth.

Sun flares give off ultraviolet light and x-rays that heat up the Earth’s upper atmosphere.

Areas on the Sun near sunspots often flare up, heating material to millions of degrees in just seconds, causing Coronal Mass Ejections (CME’s) which blast billions of tons of ionized gas into space at up to 3 million km/h.  If the gas bundle – still constrained by its own magnetic field – goes off at the right spot on the sun, it intercepts the Earth in about four days. In turn, that sets off geomagnetic storms that can damage satellites in space and shut down electrical power grids on the ground.

The Sun is also the source of the solar wind;  a flow of gases from the Sun that streams past the Earth at speeds of more than 500 km per second (a million miles per hour).  Disturbances in the solar wind shake the Earth’s magnetic field and pump energy into the radiation belts.

The solar wind and space plasma storms induce massive electrical currents that can affect power systems on the ground, especially in the north. A large storm in 1989 induced currents in the American northeast that caused a failure in the Hydro-Quebec power system that deprived 6 million people of power for over 9 hours in Canada and the United States. The same storm expanded the upper atmosphere and increased drag on NASA’s Long Duration Exposure Facility (LDEF) satellite which carried valuable specimens of materials in space exposure tests (NASA recovered LDEF before it could re-enter the atmosphere).

“Space Weather” can change the orbits of satellites and shorten mission lifetimes. The excess radiation can physically damage satellites and pose a threat to astronauts. Shaking the Earth’s magnetic field can also cause current surges in power lines that destroy equipment and knock out power over large areas. As we become more dependent upon satellites in space we will increasingly feel the effects of space weather and need to predict it.

Similar storms can set up currents that corrode the metal structure of petroleum pipelines, disrupt satellite and land-based communications, short-circuit satellite electronics, and interfere with navigational systems on ships and aircraft.

We cannot stop geomagnetic storms, but we can understand them and, eventually, predict what their effects may be in time to take measures to protect valuable power grids, satellites, aircraft, and other systems.

Tracking Solar Storms

Solar activity can be tracked by observing the number of sunspots.  Over the 11 year cycle of solar activity,  the number of sunspots seen on the Sun increases from nearly zero (the solar minimum) to over 100 at the time of the solar maximum – then decreases to near zero again as the next cycle starts.

Sunspots are places where very intense magnetic lines of force break through the Sun’s surface.  The twisted magnetic field above sunspots are sites where solar flares are observed to occur,

The last maximum occurred around 1989, and the next is predicted to fall in the year 2000.  Many solar physicists are predicting an “above average” sunspot maximum in the year 2000.  The sun now is on the upswing of its 23rd activity cycle, a numbering scheme that dates from the mid-19th century.