Magnetosphere

The sun is a frightening prospect, its extreme temperatures and pressures cause an unthinkable amount of dangerous radiation and high-energy particles to be released into the solar system. Earth is the third closest planet to the sun in our solar system, so cosmic energy from the sun is a legitimate threat. Fortunately, the Earth possesses this amazing protective forcefield called the magnetosphere that protects us from dangerous solar energy and allows us to communicate all over the world. Today we are going to dive deeper into the components of the magnetosphere, why it is important, and how it works.

Earth's Magnetosphere

The magnetosphere is an enormous magnetic field that surrounds our planet and is generated by dynamic magnetic forces within the Earth's crust. Powerful magnetism and high ionisation rates in the upper atmosphere cause particles to behave in contrasting ways to those nearer the surface of the Earth.

The other planets in the solar system possess magnetic fields, but they are much weaker than the Earth's magnetosphere, so they are affected by solar winds from the sun.

Where solar winds meet Earth's magnetic field these forces will interact, and if the solar winds are more powerful (which they often are) they will push the magnetic field back. This is why Earth's magnetosphere only extends a relatively short distance toward the sun (65,000km), but is pushed hundreds of millions of kilometres in the opposite direction by solar winds.

Our magnetosphere protects our planet from dangerous cosmic forces by Trapping solar energy inside its magnetic field (mostly in the Van-Allen belt). Cosmic forces include cosmic rays, solar winds, and coronal mass ejections.

Magnetosphere Diagram

Figure 1: labelled diagram of the Earth's magnetosphere, via Wikimedia Commons.

The effect of solar winds is shown in figure 1. These forces result in a comet-like distribution of the Earth's magnetosphere. There are some important terms you need to be familiar with:

Magnetosphere Key Terms

• Magnetopause: not marked on the diagram, but the magnetopause is the boundary between the magnetosphere and the solar winds from the sun where these two forces are in equilibrium.
• Solar plasma: solar plasma is extremely hot material that is expelled from the Sun's surface at high velocity and travels to the far reaches of the solar system.
• Bow shock: bow shock is a curved propagating disturbance that forms a comet shape. In the case of Earth's magnetosphere, this bow shock is caused by the magnetic field interacting with perpendicular solar plasma (like solar winds).
• Magnetosheath: the magnetosheath is located on the periphery of Earth's magnetic field and is synonymous with varying the direction and velocity of the magnetic field varies considerably.
• Van-Allen radiation belt: the V-A radiation belt consists of two regions of electromagnetism with a substantial number of high-energy protons and electrons. The inner belt is located between 1,000km-5,000km from Earth's surface and gains particles from interactions between neutrons and cosmic energy, while the outer belt is located between 15,000km-25,000km from the surface and is ionised by interactions with solar winds.

The Solar Cycle

The solar cycle determines the strength and velocity of solar winds travelling towards the Earth. The cycle lasts 11 years and involves the poles of the Sun's magnetic field reversing. Sunspots will appear at around 30º latitude at the start of the cycle and appear closer to the equator across the 11 years.

Magnetic Storms

Magnetic storms are instances of drastic and sudden fluctuation in magnetic fields. These storms can be short-lived but sometimes last for days at a time. Coronal mass ejections can direct masses of energetic solar matter toward the Earth's magnetic field and cause potentially uncontrollable oscillations of magnetism close to the Earth's surface. The ionosphere is disturbed in magnetic storms, so radio transmission, GPS, and power grids will be disrupted.

At higher latitudes, magnetic storms cause the Northern Lights!

Magnetosphere and Ionosphere

The magnetic currents from the magnetosphere are transferred to the ionosphere, which is nearer Earth's surface. The ionosphere contains many electrically charged particles such as ions and electrons. Interactions between solar energy and air particles cause them to become ionised, and their electrons stripped off. The ionosphere is split into 3 layers, this being the D, E, and F layers. Much like the Van-Allen belt, these layers are not independent and are merged at the boundaries. Let's have a look at each of these layers:

D-layer of the Ionosphere

Located in the upper mesosphere (70km-90km) above Earth's surface, the D-layer is unique because it completely disappears at night. This phenomenon has been proved by noticeable limitations in radio transmission (that depend on electrically charged particles in The Atmosphere) during the night. The nocturnal disappearance of the D-layer is explained by electrons reacting with oxygen ions to form non-charged oxygen molecules.

E-layer of the Ionosphere

The E-layer is located between 90km and 160km in the lower thermosphere and contains many ions and electrons that have been stripped from molecules and atoms by radiation from the sun. This is why the ionosphere depletes at night. The E-layer will deplete substantially at night time and its ionic reflective ability weakens.

F-layer of the Ionosphere

The F-layer is located in the upper thermosphere above 160km and contains the highest number of electrically charged ions and electrons out of the three layers. During night-time, the reflective power of the F-layer stays the same but the location of ions and electrons changes. An F₁ and F₂ layer forms, with the F₂ layer containing the majority of the electrically charged particles.

Figure 2: layers of the ionosphere during day and night

Hopefully this article has explained some of the more complex facts behind the magnetosphere in an easy-to-understand way. Remember, nearly all the earth's magnetic field originates from its outer core creating a magnetic field - just like a bar magnet would.