Some science behind the scenes

Sun spot activity [high]

One very key source of magnetic disturbances is ‘space  weather’ – geomagnetic storms on the sun which in turn affect the Earth.

The sun’s magnetic field varies enormously in response to fluid motions at the solar surface and in the solar interior.  Sometimes the field becomes unstable and leads to massive ejections of fluid called ‘flares’, which release magnetic energy into interplanetary space.  These eruptive phenomena are the primary drivers of what is called space weather.  In turn,  these magnetic changes, are ultimately tied to variations associated with the solar activity (or sunspot) cycle. 

The solar cycle is a spatiotemporal magnetic process unfolding over the Sun as a whole.   It is actually a magnetic cycle with an average duration of 22 years. However, because very nearly all manifestations of the solar cycle are insensitive to magnetic polarity, it remains common usage to speak of the "11-year solar cycle".

Until recently it was thought that there have been 28 cycles in the 309 years between 1699 and 2008, giving an average length of 11.04 years, but recent research has showed that the longest of these (1784–99) seems actually to have been two cycles, so that the average length is only around 10.66 years.

Cycles as short as 9 years and as long as 14 years have been observed. Significant variations in amplitude also occur.  The period between 1645 and 1715, a time during which very few sunspots were observed, is a real feature, as opposed to an artifact due to missing data, and coincides with the Little Ice Age.

 

 Cycle

Started

Finished

Duration (years)

Solar cycle 1

March 1755

June 1766

11.3

Solar cycle 2

June 1766

June 1775

9.0

Solar cycle 3

June 1775

September 1784

9.3

Solar cycle 4

September 1784

May 1798

13.7

Solar cycle 5

May 1798

December 1810

12.6

Solar cycle 6

December 1810

May 1823

12.4

Solar cycle 7

May 1823

November 1833

10.5

Solar cycle 8

November 1833

July 1843

9.8

Solar cycle 9

July 1843

December 1855

12.4

Solar cycle 10

December 1855

March 1867

11.3

Solar cycle 11

March 1867

December 1878

11.8

Solar cycle 12

December 1878

March 1890

11.3

Solar cycle 13

March 1890

February 1902

11.9

Solar cycle 14

February 1902

August 1913

11.5

Solar cycle 15

August 1913

August 1923

10.0

Solar cycle 16

August 1923

September 1933

10.1

Solar cycle 17

September 1933

February 1944

10.4

Solar cycle 18

February 1944

April 1954

10.2

Solar cycle 19

April 1954

October 1964

10.5

Solar cycle 20

October 1964

June 1976

11.7

Solar cycle 21

June 1976

September 1986

10.3

Solar cycle 22

September 1986

May 1996

9.7

Solar cycle 23

May 1996

December 2008

12.6

Solar cycle 24

December 2008

 

 

The frequency of these mass ejections or flares is dependent on the solar activity cycle. Flares of any given size are some 50 times more frequent at solar maximum than at minimum. Large coronal mass ejections occur on average a few times a day at solar maximum, down to one every few days at solar minimum.

The size of the flares is not dependent on the phase of the solar cycle. For example, three large flares occurred in December 2006, which was very near solar minimum; one of these was one of the brightest on record.

Effect on the earth

The worry for many companies is that these variations induce currents (GIC – geomagnetically induced currents) in equipment operated on the surface of Earth or in equipment operating in ‘space’. Electric transmission grids and buried pipelines are common examples of such conductor systems, but satellites and other communications equipment are also at risk. GIC can cause problems, such as increased corrosion of pipeline steel and damage to high-voltage power transformers. It can simply knock the systems out.

In effect, a time-varying magnetic field external to the Earth induces electric currents in whatever happens to be capable of producing a current on the ground.

Examples of conducting networks are electrical power transmission grids, oil and gas pipelines, undersea communication cables, telephone and telegraph networks and railways. All these currents tend to be low frequency and are often described as being quasi direct current (DC), although the variation frequency of GIC is governed by the time variation of the electric field.

Since the largest magnetic field variations are observed at higher magnetic latitudes, GIC have been regularly measured in Canadian, Finnish and Scandinavian power grids and pipelines since the 1970s. GIC of tens to hundreds of Amperes have been recorded. GIC have also been recorded at mid-latitudes during major storms. There may even be a risk to low latitude areas, especially during a storm commencing suddenly because of the high, short-period rate of change of the field that occurs on the dayside of the Earth.

GIC have been known since the mid-19th century when it was noted that electrical telegraph systems could sometimes run without power during geomagnetic storms.

Time span of effect

 Solar flares produce ultraviolet radiation, sometimes x-rays and high energy cosmic rays.  These forms of radiation propagate at or near the speed of light reaching the earth in about 8 to 15 minutes, where they cause ionisation and electric currents in the ionosphere.  In turn the ionospheric disturbances cause variations in the magnetic field which, when strong enough, are called magnetic storms.

Flares also produce corpuscular radiation particles which propagate more slowly, reaching the earth in about one or two days.  When these charged particles hit the upper atmosphere, they also produce ionisation.  Some are trapped in the magnetosphere, where they are temporarily stored.  When sufficiently accelerated in the magnetosphere, they may penetrate deep enough into the atmosphere to produce auroras.  Perturbations of the earth's magnetic field are associated with these events.

In effect, magnetic storms occur at two times and the second time offers us the possibility to plan a means to take advantage:

  • immediately after a solar flare – due to wave radiation
  • sometime after the solar flare – generally about 2 to 4 days – due to corpuscular radiation.

The so called 'KP' index becomes a maximum on the fourth day following a solar flare [source Reiter and Reinhold – Relationships between atmospheric electrical phenomenon and simultaneous meteorological conditions – Air Force Cambridge Research Laboratory 415 1960].  Magnetic storms often last several days.  So we have an opportunity here to exploit this phenomenon.

Observations

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