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Earths Magnetic Field

Bulk of this page is supplied by NASA and NICT with small input from SWSBOM

Earth’s magnetic field – Also known as the geomagnetic field, is the magnetic field that extends from the Earth’s interior out into space, where it interacts with the solar wind, a stream of charged particles emanating from the Sun. The magnetic field is generated by electric currents due to the motion of convection currents of a mixture of molten iron and nickel in the Earth’s outer core: these convection currents are caused by heat escaping from the core, a natural process called a geo-dynamo. The magnitude of the Earth’s magnetic field at its surface ranges from 25 to 65 μT (0.25 to 0.65 gauss). As an approximation, it is represented by a field of a magnetic dipole currently tilted at an angle of about 11 degrees with respect to Earth’s rotational axis, as if there were an enormous bar magnet placed at that angle through the center of the Earth. The North geomagnetic pole actually represents the South pole of the Earth’s magnetic field, and conversely the South geomagnetic pole corresponds to the north pole of Earth’s magnetic field (because opposite magnetic poles attract and the north end of a magnet, like a compass needle, points toward the Earth’s South magnetic field, i.e., the North geomagnetic pole near the Geographic North Pole)

As far as we know currently the earths magnetic field is believed to look similar to this.

Magnetosphere, Magnetopause – Our planet Earth has an intrinsic magnetic field. Charged particles become trapped on these magnetic field lines, forming the Earth’s magnetosphere. The impact of solar wind particles causes the lines facing the Sun to be compressed. On the other hand, the magnetic field lines facing away from the Sun get stretched and elongated, forming the Earth’s magnetotail.

A number of layers and boundaries can be observed in near-Earth space where the solar wind and Earth’s magnetic field meet. The first is the Earth’s bow shock created when the supersonic solar wind is suddenly slowed as it approaches the magnetosphere. The edge of the magnetosphere is known as the magnetopause. There are two weak points in Earth’s defenses, cusps which occur above the planet’s north and south magnetic poles. Particles from the solar wind leak into the magnetosphere towards the Earth along magnetic field lines and cause the auroras.

https://www.mps.mpg.de/planetary-science/planetary-plasma-environment

Monitoring the Magnetosphere – The following is a simple static video that shows the amount of activity that occurs in our magenetosphere in one day. This is from sws.bom.gov.au and was from a day where we saw coronal hole stream energy impacting and causing fluctuations. This data cannot be streamed as it is selectable by date and I will look to use the raw data in my own visualization later on.

Geomagnetically induced currents – Geomagnetically induced currents, affecting the normal operation of long electrical conductor systems, are a manifestation at ground level of space weather. During space weather events, electric currents in the magnetosphere and ionosphere experience large variations, which manifest also in the Earth’s magnetic field.

Why do we know about these induced currents? Over the last 200 years with our rampant modernization of the world through the use of electricity we have seen multiple solar based events create mainly minor damage. However some larger events that occur less regularly can impart enormous amounts of induced current into major electrical transmission lines, oil pipelines, water pipelines, railroad tracks, communications and general systems powered by electricity. We will discuss how to prepare for these events under the “preparing” menu item.

Thanks to NASA JPL

Magnetic Field Strength

Since the discovery of the earths magnetic field we have been monitoring its strength along with tracking the polar locations. The magnetic field of earth is like the roof over our heads and protect us from bad weather. We have tracked its field strength

At present, the overall geomagnetic field is becoming weaker. The present strong deterioration corresponds to a 10–15% decline over the last 150 years and has accelerated in the past several years. Geomagnetic intensity has declined almost continuously from a maximum 35% above the modern value achieved approximately 2,000 years ago. The rate of decrease and the current strength are within the normal range of variation, as shown by the record of past magnetic fields recorded in rocks. The Earth’s magnetic north pole is drifting from northern Canada towards Siberia with a presently accelerating rate—10 kilometers (6.2 mi) per year at the beginning of the 20th century, up to 40 kilometers (25 mi) per year in 2003, and since then has only accelerated.

Galactic Cosmic Rays – (GCR) Cosmic rays are high-energy protons and atomic nuclei which move through space at nearly the speed of light. They originate from the sun, from outside of the solar system, and from distant galaxies. Upon impact with the Earth’s atmosphere, cosmic rays can produce showers of secondary particles that sometimes reach the surface

By NASA/JPL-Caltech/SwRI – http://photojournal.jpl.nasa.gov/jpeg/PIA16938.jpg, Public Domain

The following diagram shows the interaction of the Cosmic ray with our magnetic field. A cosmic ray approaching Earth first encounters Earth’s magnetic field. The magnetic field repels some particles altogether. Those that get through are deflected by the magnetic field. When the primary cosmic ray strikes an atom in Earth’s atmosphere, the collision may produce one or more new energetic particles called “secondary” cosmic rays. These secondary particles strike other atmospheric atoms producing still more secondary cosmic rays. The whole process is called an atmospheric cascade. If the primary cosmic ray has enough energy — greater than 500 million electron volts — the nuclear byproducts of the cascade can reach Earth’s surface.

Monitoring of Cosmic Rays – Since the 1960’s there has been a increased understanding of the need to monitor these powerful forms of energy entering our biome. This understanding commenced once early Astronauts and Cosmonauts on returning from space outside the earths magnetic field described seeing lights flashing in their eyes in the dark with their eyes closed. This was later confirmed to have created macular degeneration or cataracts. Later DNA testing confirmed those who had been beyond the magnetosphere had minor changes in their DNA as well. This testing was possible due to blood tests taken before and after the trips.

Earth climate shift via Cosmic Rays – Henrik Svensmark, physicist and professor in the Division of Solar System Physics at the Danish National Space Institute (DTU Space) in Copenhagen, released a journal paper in 2007 describing the forcing mechanism of cosmic rays potential for creating additional cloud coverage. The hypothesis, verified by experiments, is that electrons released in the air by the passing muons promote the formation of molecular clusters that are building blocks for cloud condensation nuclei.

Tests to prove the theory – Putting this theory into extensive testing was required to prove its validity. Two experiments were created with the second one being run in an attempt to debunk the theory, when it actually found the theory to be solid. Svensmark conducted proof of concept experiments in the SKY Experiment at the Danish National Space Institute. This investigated the role of cosmic rays in cloud formation low in the Earth’s atmosphere, the SKY experiment used natural muons (heavy electrons) that can penetrate even to the basement of the National Space Institute in Copenhagen. The hypothesis, verified by the experiment, is that electrons released in the air by the passing muons promote the formation of molecular clusters that are building blocks for cloud condensation nuclei.

The second test was performed have presented the main outcomes of 10 years of results obtained at the CLOUD experiment performed at CERN. They have studied in detail the physio-chemical mechanisms and the kinetics of aerosols formation. The nucleation process of water droplets/ice micro-crystals from water vapor reproduced in the CLOUD experiment and also directly observed in the Earth atmosphere do not only involve ions formation due to cosmic rays but also a range of complex chemical reactions with sulfuric acid, ammonia and organic compounds emitted in the air by human activities and by organisms living on land or in the oceans.

Monitoring Cosmic rays world wide

Each of the major government space or weather agencies in developed nations have some form of cosmic ray detection system. Each of them are unique due to their elevation and location which changes their baseline values. Those located on mountain tops record far higher levels than those located near sea level. This is due to the apparent dispersion of GCR’s through the atmosphere.

NOTE: Not all reporting locations are equal, not all equipment is equal. Be careful about making statements that one area of the planet is seeing an exponential increase when others are not. Many detectors are designed and built to a specification where limitations are likely to be causing erroneous data.

Cosmic-ray exposure anywhere in the atmosphere based on the cosmic-ray observations at the ground level and geostationary orbit. The data are updated at intervals of 5 min and 1 day during solar storm and quiet periods, respective.

Link to Cosmic Ray Monitoring

Van Allen Belts

There is an area in the space around the Earth where high-energy particles exist that we refer to as a “radiation belt”. In 1958, Dr. James Van Allen at the University of Iowa discovered this radiation belt. Van Allen launched the Explorer 1 and 3 spacecraft, which were equipped with a Geiger counter to measure cosmic ray. After the launch, the Geiger counter picked up unexpected values that were sometimes too high and sometimes too low. After this, Explorer 4 and Pioneer 3 were equipped with improved instruments that revealed that the unexpected values indicated the existence of high-energy particles around the Earth

https://aer-nc-web.nict.go.jp/radi/en/radio/

Radiation belts are circularly trapped around the Earth and are separated into two regions: inner and outer. The electron flux of the inner belt has a peak around 1.5–2 Earth radii distance (about 3,000 km) from the center of the Earth, while the outer belt has a maximum flux around 4–5 Earth radii (about 20,000 km). A part of the outer radiation belt reaches the geostationary orbit, which is located at about 6.6 Earth radii from the center of the Earth. The region between the inner and outer radiation belt is referred to as the slot region, where the electron flux intensity is weak compared with the other two regions.
The outer radiation belt is fairly variable. Solar wind conditions, which affect the magnetosphere, cause strong enhancement and/or loss of the electron flux, whose variation sometimes increases/decreases by a few orders of magnitude. The risk of spacecraft anomalies tends to increase if the spacecraft experiences a strong enhancement of the flux.

Electrons, which are negatively charged, move along the magnetic field line. It is difficult for electrons to move perpendicular to the magnetic field without any force caused by the electric field or gradient of magnetic field intensity. During parallel motion, some electrons are reflected by force related to conversing the magnetic field line near the north/south polar region before they reach the atmosphere. Some electrons precipitate into the atmosphere and collide with atmosphere molecules, after which they lose their energy. Some of them return to the magnetosphere, but others do not. Thanks to the atmosphere, which prevents the penetration of high-energy electrons, even 1 MeV electrons cannot reach heights less than 80–90 km from the ground.
Above Brazil, the magnetic field intensity is relatively weak compared with other regions. This is referred to as the “South Atlantic Magnetic Anomaly”. In this region, the magnetic field conversing effect is relatively weak, which enables high-energy particles to penetrate more deeply into the atmosphere. This means that spacecraft and astronauts working within a few hundred altitudes of the South Atlantic area may have an increased risk of hazards associated with radiation. Moreover, there are some reports that instrument anomalies tend to increase in the South Atlantic area.

The suns activity and the Van Allen Belts

The sun releases the solar wind, which is a combination of the flow of high-speed charged particles (plasma) and the sun’s own dragging magnetic field (or “interplanetary magnetic field” (IMF)). The speed of the solar wind is usually about 400-450 km/s near the Earth.
The solar wind is not steady: coronal mass ejection (CME) suddenly releases a large amount of solar corona mass, and the co-rotating interaction region (CIR) where the fast solar wind interacts with the slow wind creates the compressed plasma and IMF. These lead to a strongly turbulent state of the solar wind for several hours. When the “active” solar wind blows the earth’s magnetic field (magnetosphere), the high-energy electrons of the radiation belt are enhanced in and/or lost from the magnetosphere.

Process of radiation belt enhancement and loss

Electron acceleration and loss mechanisms in the magnetosphere control the electron flux variation of the radiation belts. The nonlinear nature of plasma in a non-uniform magnetic field makes it difficult to understand the physics associated with the acceleration and loss. Much research attention has been devoted to identifying the mechanisms associated with solar wind activity, with recent studies indicating that the CIR is more effective than the CME in terms of enhancing the electron radiation belt. Here, we briefly describe the processes associated with radiation belt acceleration (enhancement) and loss.

Electron acceleration

If low-energy electrons are accelerated and energized, the number of high-energy electrons and their electron flux in the high-energy range increases. There are two acceleration properties: adiabatic and non-adiabatic acceleration.

Adiabatic acceleration

This process increases charged-particle energy by dragging a particle into a region in which the magnetic field intensity is stronger.

Non-adiabatic acceleration

This process accelerates electrons at a local position through wave-particle interactions that break the first-adiabatic invariants.

One cause of adiabatic acceleration is ultra-low-frequency (ULF) waves in the magnetosphere. This oscillation transports radiation belt electrons in both the inward and outward directions. Electrons transported in the inward/outward direction experience stronger/weaker magnetic fields, and thus the adiabatic process increases/decreases the electron energy. The total electron energy and total amount of electron flux in the radiation belt increase if the number of electrons transported in the inward direction is higher than the number of electrons transported in the outward direction.
The most important element in the non-adiabatic acceleration of an electron is wave-particle interactions between electromagnetic waves and electrons. A whistler wave, which is one of the waves in plasma, can effectively scatter electrons in very short time scale (less than sec. order). Scattering associated with whistler waves both increases/decreases the electron energy and changes their trajectories.

Electron loss

Electron loss is identified with decrease of the number of electrons in a certain energy range. There are two reasons this can happen.

  • Electrons decrease their energy (1)
  • Electrons escape from the magnetosphere (2)

Process (1) occurs when a magnetic storm develops and the magnetic field intensity in the inner magnetosphere decreases. This decrease prompts the adiabatic effect to reduce electron energy, which is referred to as “adiabatic loss”. If adiabatic loss is dominant during a magnetic storm, the electron energy recovers its pre-storm time energy after the storm declines. However, in many cases, the electron energy of the radiation belt increases or decreases compared with the energy in the pre-storm time, suggesting that the acceleration and/or loss processes associated with the non-adiabatic effect during the magnetic storm time vary the electron energy of the radiation belt. Process (2) is divided into two processes: electron precipitation into the Earth’s atmosphere, and magnetopause shadowing.

Precipitation

Charged particles with gyromotion move parallel to a magnetic field line. The Earth’s magnetic field intensity increases towards the North and South poles. Because of the magnetic field convergence, some charged particles are reflected before reaching the atmosphere by the magnetic mirror force. Note that the mirror force reflects the particles more effectively when the gyrating particle trajectory is more perpendicular to the magnetic field line. These particles are permanently trapped between the Northern and Southern hemispheres if there is no scattering that changes their trajectories. When a geomagnetic storm occurs, plasma waves (e.g., whistler waves, ion cyclotron waves) are generated in the magnetosphere and scatter the trapped electrons, changing their trajectories. Some electrons precipitate into the Earth’s atmosphere without enough magnetic mirror force. Some of these precipitated electrons cannot return to the magnetosphere, so the trapped electron population decreases non-adiabatically.

Magnetopause shadowing

Electrons move not only in the parallel direction between the Northern and Southern hemispheres but also in the perpendicular direction of both the magnetic field and its gradient. If the Earth’s magnetic field is symmetric at the polar axis, the perpendicular drift motion is entirely in the longitudinal direction. This drift motion is eastward for electrons (negatively charged particles) and westward for protons (positively charged particles).
When the solar wind dynamic pressure becomes strong, the magnetosphere is compressed. Then, the boundary of the magnetosphere interacts with the inner drift paths of electrons. If the electrons drifting around the Earth interact with the magnetopause boundary, they escape into interplanetary space. This is one of processes that decreases the number of electrons trapped in a radiation belt.

Many scientists who specialize in observation, theory, and computer simulation have been attempting to improve our understanding of the physics of radiation belts for over 50 years.

A spacecraft can become electrically charged if it is in an environment where it interacts with charged particles. If the charging exceeds a breakdown voltage between materials, a discharge can happen suddenly and cause damage to instruments, intermittent anomalous behavior, and catastrophic satellite failure. Spacecraft charging includes “surface charging” and “internal dielectric charging”. Surface charging is due to relatively low energy electrons around keV energy, while internal dielectric charging is due to electrons with relativistic energy.

Surface charging

When electrons with energy less than 100 keV collide with the surface of a spacecraft, a negative electric charge occurs on the surface (surface charging). After the charging, electrons tend to be reflected due to the negative potential of the spacecraft. Several release effects of the negative potential simultaneously occur, and the charging and release effects are thus balanced in a relatively quiet geospace environments and the surface charging is not so serious for the spacecraft. However, as the number of keV-electrons suddenly increases, the electric potential between materials (i.e., cables and circuits) suddenly increases. This may cause a breakdown, which is a source of the electric current associated with the discharge. This is what damages the spacecraft.

Internal dielectric charging

Electrons with energy larger than 100 keV can actually penetrate into the spacecraft. These high-energy electrons are what cause the charging on electric circuits and cables in the spacecraft (internal dielectric charging). When the number of high-energy electrons increases after a geomagnetic storm, a spacecraft has an increased risk related to the internal charging.

2 MeV electron flux distribution (GEMSIS-RB simulation: Past 30 days)

Colors show 2 MeV electron flux distribution on x-y (left) and x-z (right) plane.
Red color shows high flux level.
Right panel: Left direction (+X direction) is towards the sun. +Z direction is towards the north. The X-Z plane includes the earth’s center.
Left panel: Left direction (+X) is towards the sun. +Y (-Y) area has the down (dusk) sector. The X-Y plane includes the earth’s center.
You can watch the flux variation past 30 days in this movie which updates daily.

Geomagnetic anomaly map

Animation of secular variation in geomagnetic total intensity for the last 400 years

Current Magnetic and Geomagnetic Pole Locations

North Pole

South Pole