There is a clear link between solar activity and effects observed in space directly around the Earth. This space weather results from dynamic events within the Sun’s atmosphere.
This article first explores the mechanisms that cause dynamic events in the Sun’s atmosphere before exploring how they affect space around Earth. Finally, it explores the effects that solar activity has on humans.
The 22-year solar cycle is a function of the Sun’s dynamic magnetic field (Freedman and Kauffman). Babcock’s magnetic-dynamo model, first developed in the 1960s, explains many of the observed solar phenomena. Prior to the 1960s, a sound foundation had been laid from which Babcock could construct a model to explain solar observations.
Babcock’s model had to explain a number of important phenomena observed on the Sun. It had to account for the:
reversal of the main magnetic field.
development of sunspots at 300 north and south before migrating towards the equator.
discovery that sunspots have strong magnetic dipolar fields in which the preceding and following members are opposite in the north and south hemispheres. Preceding members tend to be stronger and slightly closer to the equator.
development of bipolar magnetic fields (BMRs,) that give rise to sunspots and disappear by expanding and their migration towards the pole in their hemisphere.
A global model also has to take into account the motion of conducting plasma that would affect the embedded magnetic force lines. It had already been discovered that magnetic pole reversals occur approximately every 11 years at sunspot maxima.
An important observation that held the key for a solar cycle model was the differential rotation within the Sun. This provides both the probable source of the Sun’s magnetic field and the solar cycle. The Sun’s magnetic field is thought to be generated in the zone between the radiative and convection zones (Weiss and Thompson, 2009). Differential rotation between the two zones provides the mechanism to produce the magnetic field. Also, differential rotation within the convective zone between the equator and the poles gives rise to the solar cycle (Babcock, 1961).
In Babcock’s model, the magnetic field is at its simplest at the start of a cycle. The magnetic field lines emanate from the north pole and loop around to the south pole. Only latitudes greater than 55 are affected by the field. This is the state three years before a new sunspot cycle begins.
With the passage of time, the magnetic field lines submerged in the convection zone become drawn out due to differential rotation. The magnetic field becomes wrapped and approaches a near east-west orientation. This wrapping causes amplification of the field. After three years, a critical magnetic field limit is reached at latitudes 300 north and south of the equator. The critical limit will be met at lower latitudes later in the cycle. The wrapping of the magnetic field will give rise to irregularities leading to distortions and the formation of ‘flux ropes.’ The instabilities result in the formation of loops (see fig. 1.)
Figure 1: The development of the wrapping of the magnetic field lines and the creation of loops in flux ropes from the surface of the photosphere into the Sun’s atmosphere. Note that the preceding members in each hemisphere are opposite in polarity (Adapted from Freedman and Kauffman)
As distortion continues, buoyancy effects due to the strengthening magnetic field result in the upward lifting of the flux rope. They may break the photosphere surface to form BMRs. The magnetic field lines (defined by plasma being drawn along magnetic field lines) arc into the higher atmosphere, forming coronal loops. Sunspots occur in BMRs when they are young and compact, and when the magnetic field is strong enough to inhibit convection. Thousands of BMRs may be formed during a single sunspot cycle. The magnetic field associated with these zones can be hundreds of times that of the main field (SPACEweb).
Coronal loops partly dissipate the magnetic field throughout the sunspot cycle. During the sunspot cycle, sunspots are dissipated as the preceding members expand, are drawn out and migrate towards the equator. Likewise, the following members expand, are drawn out and migrate towards the pole. During the dissipation of the BMRs, magnetic flux loops are liberated into the corona. This process leads to the magnetic field becoming weaker.
As the coronal loops from the BMRs expand towards each other and towards the flux loops from the north and south poles, they are realigned. As the field lines rise, they may pinch and reconnect, releasing energy and ejecting solar material from the corona. This is important for the coronal mass ejections.
As this process proceeds, the magnetic field is dissipated, forming a new global, opposite-polarity magnetic field. A new cycle begins. Once the polarity again changes, a complete 22-year cycle is concluded.
There are a number of problems with the dynamo model. First of all, the reversal of the Sun’s magnetic field is not fully understood. Also, it doesn’t explain why sunspot activity can disappear for many years. An example of this is from 1645 to 1715. During this same period, there were climatic changes in Europe and the USA. Also, higher temperatures appear to have been associated with increased sunspot activity in the eleventh and twelfth centuries.
Solar Weather
Solar phenomena give rise to changes in the physical conditions in space that affect human technology and life on Earth. The change in the conditions near Earth called space weather. Three solar phenomena give rise to adverse space weather: coronal mass ejections, flares and coronal holes. Before considering the effects of space weather on Earth the source of the influences on space weather should be detailed in reference to how they are linked to the solar cycle.
Coronal Mass Ejections
Coronal mass ejections (CMEs) are large eruptions that eject mass and the Sum’s magnetic field into interplanetary space (Gopalswamy, 2007). CMEs produce solar energetic particles (SEPs) and geomagnetic storms in the Earth’s magnetosphere. They are the largest single-event triggers for adverse space weather.
CMEs originate from the closed magnetic fields associated with active regions and quiescent filament regions (Gopalswamy et al, 2009). Typically, they are more prevalent while the sunspot areas are on the increase and decrease than at sunspot maximum. During sunspot maximum periods, CMEs originate from higher latitude non-active regions of the Sun.
CMEs commonly result from the reconnection of coronal flux loops. As with flares, CMEs form shock waves in the interplanetary medium. CMEs result in a larger release of energy from flares with increased effects on space weather.
Solar Flares
Solar flares result from releasing twisted magnetic fields above or near sunspots (SPACEwebb). The buildup of the magnetic field may occur over several days and be released in one minute. This release produces a radiation burst ranging from radio waves to gamma-rays. The amount of energy released may be equivalent to millions of 100-megaton hydrogen bombs simultaneously exploding (HESPweb). The release accelerates electrons, protons and heavy nuclei. Flares extend through the chromosphere and into the corona. As they are associated with sunspots, solar flares are most common at the height of sunspot activity.
Coronal Holes
Coronal holes significantly affect solar weather (Vršnak, Temmar and Veronig, 2007). During quiet periods, these features are found at the solar poles. During active periods, they may also form at lower latitudes, where they are more likely to allow emissions towards Earth. Coronal holes are dark areas in the corona where open magnetic fields are present and have a reduced electron density (Navarro-Peralta and Sanchez-Ibara, 1994). They are a source of fast components of the solar wind.
As the fast solar wind interacts with the slower component, it increases in density, and a magnetic field develops, resulting in a shockwave. The kinetic energy of the fast component is also converted to heat.
The changes in the interplanetary magnetic field caused by coronal holes can cause long-lasting geomagnetic storms, which may last for several days. These storms are less severe than those caused by coronal mass ejections but more stable. Coronal hole events may prolong the effects of coronal mass ejections.
Effect on the Earth and Humans
The Sun emits a steady stream of solar wind that is mainly deflected by the Earth’s magnetosphere. Energetic events in the Sun’s atmosphere, as described above, can cause adverse space weather conditions that can damage equipment and endanger life.
Space weather can be affected by three different factors: magnetic storms, SEPs and electromagnetic radiation (Hochedez et al, 2005). Geomagnetic storms are commonly caused by the shockwaves created by CMEs that change the interplanetary magnetic field (IMF.) The solar wind carries the Sun’s magnetic field to form the IMF. However, magnetic storms can also occur due to changes in the solar wind due to high speed flows from coronal holes. The IMF interacts and disturbs Earth’s magnetic field. Flares tend to cause x-ray and UV radiation that causes disturbances in the ionosphere. CMEs and flares create SEPs that can damage electronic equipment.
Under normal conditions, the magnetosphere deflects solar winds. The magnetosphere and interplanetary magnetic field are in contact at the magnetopause. The two fields can link up across the magnetopause, allowing the solar wind to enter Earth’s atmosphere. This allows for ‘solar wind gusts,’ flares and CMEs that are emitted towards the Earth to inject matter and energy into the magnetosphere. It is these injections that cause magnetic storms.
Solar flares emit x-rays and UV that can interfere with the ionosphere and cause communication problems.
A change in the unrelenting solar wind by active solar events leading to adverse space weather can result in a number of effects on humans:
Satellite drag caused by atmospheric density changes.
Satellites sensor damage by charged particles.
Geomagnetically induced currents in power grids and pipelines
Increased radiation threat for passengers on high flying aircraft and spacecraft.
High frequency communications blackouts in polar regions.
The largest known magnetic storm occurred in 1859. It was named the Carrington Event after Richard Carrington, who observed the solar flare that gave rise to the storm. The associated aurora (resulting from charged particles cascading through the atmosphere) was observed as far south as Cuba. The magnetic storm caused damage to communication equipment. It is estimated that if a similar event took place today the repair costs would amount to two trillion dollars in the USA.
Power grids are also vulnerable to induced currents from magnetic storms. In 1989, a large magnetic storm left 6 million people without electricity for 9 hours in Quebec, Canada. The storm was triggered by a CME and caused currents that caused a transformer to fail.
Satellites are particularly vulnerable to space weather. In 1994, a magnetic storm affected three communication satellites. The two Canadian satellites, Anik E1 and E2, were affected by induced currents that disrupted their guidance circuitry. Only one of the satellites was recovered. The cost was $228 million for the lost satellite and $3 billion in lost revenue. The same storm also affected the Inelsat K satellite.
Atmospheric drag may affect low-altitude satellites. During magnetic storms, the atmosphere expands. Increased density results in unpredicted drag on satellites in low orbit. This can result in an earlier re-entry than expected, reducing the life of satellites, as occurred with Skylab.
X-ray and ultra-violet radiation from flares can increase the ionisation of the ionosphere, leading to high-frequency communication problems. This can impact trans-polar flights, leading to added costs to airlines due to flights being diverted to avoid polar regions during magnetic storms.
Key Takeaways
Solar-Earth Connection
Space weather results from dynamic events in the Sun’s atmosphere
These events directly affect the space around Earth and human activities
Solar Cycle & Babcock’s Model
22-year solar cycle driven by Sun’s dynamic magnetic field
Babcock’s magnetic-dynamo model (1960s) explains:
Magnetic field reversals every 11 years
Sunspot development and migration patterns
Formation and behavior of bipolar magnetic regions (BMRs)
Key Solar Phenomena
Coronal Mass Ejections (CMEs)
Largest single-event triggers for adverse space weather
Release mass and magnetic field into space
Solar Flares
Release twisted magnetic fields near sunspots
Produce radiation from radio waves to gamma-rays
Coronal Holes
Source of fast solar wind components
Can cause long-lasting geomagnetic storms
Effects on Earth and Humans
Major impacts include:
Satellite damage and drag
Power grid disruptions
Communication blackouts
Increased radiation exposure for high-altitude flights
Geomagnetically induced currents in infrastructure
Historical Events
1859 Carrington Event: Largest recorded magnetic storm
1989 Quebec blackout: 6 million people affected
1994 Satellite failures: Over $3 billion in damages
I found astronomy while working in dark rural locations. Initially, I explored the night sky and learnt the constellations before purchasing a pair of binoculars to further my knowledge of the sky.
My first telescope was a 200 mm Newtonian reflector on an equatorial mount. I found that this telescope had a steep learning curve but was a rewarding experience.
As time progressed, I became interested in astrophotography. This resulted in purchasing a 110 mm refracting telescope and a dedicated monochrome-cooled astronomical camera. This resulted in another very rewarding steep learning curve that far surpassed the experience with my first telescope.
I have joined Telescope Guru to share my knowledge of telescopes and astronomy.
