Wolf Number & Carrington Event in context with Solar Storms

In simple words, Solar storms are a natural occurrence caused by high-energy particles hitting the Earth. These high-energy particles are released in the explosive outbursts from the Sun. Here is some description about the fundamental concepts:

• We all know that every 11 years, a pattern of frequency and placement of sunspots visible on the Sun is repeated, which is called Solar Cycle.
• The variation in the sun causes changes in not only space weather but also to some degree weather and climate on earth, mainly due to periodic change in the amount of irradiation from the Sun that is experienced on Earth. The basic causes of the solar variability and solar cycles are not concretely defined.
• Some researchers have linked them to the tidal forces of gas giants such as Jupiter and Saturn. Some link them to solar inertial motion.

During the active part of the solar cycle, there are more sunspots, relative to other times. This number is measured in Wolf number or International sunspot number or Zürich number. This Wolf number has been collected and tabulated by researchers for over 150 years. They have found that sunspot activity is cyclical and reaches its maximum around every 9.5 to 11 years, thus giving rise to the phenomena of solar cycle.

With the Sun in an active part of its cycle, there are concerns that the increased irradiation, magnetic waves, extreme ultraviolet rays etc. affect life on earth. Some storms could disrupt technology on Earth including satellite navigation signals and aircraft communications.

The question is how an outburst on the Sun can cause a storm on Earth?

• The disturbance in the interplanetary medium which drives the geomagnetic storm may be due to a solar coronal mass ejection (CME) or a high speed stream (co-rotating interaction region or CIR). Often an intense burst of radiation called a solar flare appears when magnetic energy – stored in sun’s atmosphere – is suddenly released.
• Solar flares are sometimes associated with the release of high energy particles into space – eruptions that are known as coronal mass ejections (CMEs), though these can also occur on their own. A large CME can contain billions of tonnes of gas and other matter that pours into space at several million km per hour. The charged particles in this cloud stream towards any planet or spacecraft in its path. When these particles collide with the Earth, they can cause a geomagnetic storm – a disturbance in the magnetic sheath (or magnetosphere) that surrounds our planet, protecting its denizens from the worst effects of cosmic rays.

Many of the effects of charged particles hitting the Earth’s magnetosphere are benign, such as polar lights – the Aurora borealis and australis. Geomagnetic storms – often referred to as solar storms – cause these northern or southern lights to become visible at lower latitudes.

However, the malign effects are that they disrupt technology on Earth, such as communications systems – including those used by aircraft, satellite navigation signals and electrical power grids. They could wreak long-lasting havoc with communications and power infrastructure across the globe.

As we read above, the sun goes through cycles of high and low activity that repeat approximately every 11 years. It is currently gaining in activity and is expected to peak in 2013 or 2014. This means that in recent future, we can expect more solar flares and more coronal mass ejections. The solar cycle we’re currently in has been a relatively quiet one in compared with previous ones.

Some past impacts of soar storms are as follows:

• In 1994, a solar storm caused major malfunctions to two communications satellites, disrupting television and radio services throughout Canada.
• In 1989, another event caused the Hydro-Quebec power grid in Canada to go down for over nine hours. The resulting damages and loss in revenue were estimated to be in the region of hundreds of millions of dollars.

Most significant historic event remains the great solar storm of 1-2 September 1859. These disturbances shorted telegraph wires, starting fires in North America and Europe, and caused bright aurora to be seen in Cuba and Hawaii. This is called Carrington Event. In 1859, our technological infrastructure was in its infancy, but today a Carrington Event can cause more damages than we imagine.