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Magnetosphere
>General description
This is the region of space surrounding Earth in which its magnetic field is dominant.
This area encasing Earth is a result of its intrinsic magnetic field, the solar wind plasma and the interplanetary magnetic field.
The side of the Earth upon which the solar wind plasma is incident is compressed to a distance between 10-15 times the Earth’s radius (RE). The other side of the magnetosphere, the ‘night’ side, is a magnetospheric cavity elongated by the solar wind flowing past the Earth – this is called the magnetotail and its distance is estimated to be approximately 3000RE, however, the exact value is unknown.
This area encasing Earth is a result of its intrinsic magnetic field, the solar wind plasma and the interplanetary magnetic field.
The side of the Earth upon which the solar wind plasma is incident is compressed to a distance between 10-15 times the Earth’s radius (RE). The other side of the magnetosphere, the ‘night’ side, is a magnetospheric cavity elongated by the solar wind flowing past the Earth – this is called the magnetotail and its distance is estimated to be approximately 3000RE, however, the exact value is unknown.
Image of the Magnetosphere. Image courtesy: Wikipedia
>Interaction with the Sun
- Solar wind is constantly ejected from the Sun and comprises of ionised particles which are travelling at supersonic speeds and carry with them the Sun’s interplanetary magnetic field.
- Due to the supersonic speeds of these ions, upon collision with the Earth’s magnetic field a shock wave is formed not dissimilar to a sonic boom. This shockwave is known as the bow shock.
- The boundary of the interaction between the incident ions and the Earth’s magnetic field is a region called the magnetopause. The distance of this boundary from the Earth can fluctuate depending on the strength of the solar wind.
- Most of the ionised particles that hit the magnetopause are deflected and swept back passed the Earth into a long cylindrical extension of the magnetosphere called the magnetotail, while the ones that penetrate become confined in an orbit and form part of the energetic Van Allen radiation belts.
- The magnetotail acts as a reservoir for plasma and energy, which is released into the inner magnetosphere at various intervals during magnetospheric substorms. The magnetotail is split into two regions called the ‘lobes’ by the Equatorial Current Sheet. In between the lobes there is an area containing extremely hot ions and electrons – this is called the plasmasheet.
- When the IMF and Earth’s magnetic field connect it results in the transfer of energy, by a process called reconnection, from the solar wind to the magnetosphere, and by extension from the Sun’s atmosphere to the Earth’s atmosphere. Upon connecting, ionised plasma flows into the Earth’s magnetic currents and can build up at certain points – ultimately causing sub storms and magnetic storms. A second primary reconnection point on the antisolar side of the Earth reverses the flow of ionised plasma, returning it into the solar wind to flow past the Earth.
- The solar wind ions can sometimes be injected into the magnetosphere and follow the magnetic field lines into the Earth’s upper atmosphere. This can cause the atoms in the upper atmosphere to become excited and release photons – this is what causes the phenomenon known as the Aurora Borealis.
Characteristics
Firstly, the magnetic field is generated by the Dynamo effect. This means that the field is generated through the relative motion of the earth and charged particles (in this case liquid metallic iron in the earth outer core) by convection and is thought to produce a current, which generates the magnetic field.
The magnetic field can be thought of as a bar magnet that is tilted 11 degrees from the earth’s spin axis and a magnetic dipole that is positioned at the centre of the earth. The dipole has its South pole pointing towards the geomagnetic North pole, and its North pole pointing towards the geomagnetic South pole. The reason being because the magnet attracts a magnet that has an opposite pole and has the characteristic of repelling a magnet that has the same charge.
Magnetic field density is the unit that shows how strong a magnetic field is. It varies at different positions of the earth. The intensity of the field is lowest near the Equator and greatest near the South and North poles. The field density can be measured in gauss and nanoteslas.
Magnetic fields can vary if disturbed by another magnetic field or from charged particles. The disturbance that the earth mainly receives is from the solar wind(produced by the solar flare on the sun). The solar wind is a stream of charged particles emitted by the Sun that gets trapped in Earth's Van Allen radiation belt, the charged particles can then interact with the Earth’s magnetic field which will then lead to an increased amount of energy entering into the magnetosphere (the earth’s magnetic field deflects the solar wind to form a bounded comet-shaped region surrounding the Earth). The phenomena can only be observed if the amount of charged particles is high enough. If so, it can form magnetic storms which can then lead to blackouts and disruptions in artificial satellites accompanied by the display of the northern lights (it is the natural light can be observed at high latitude).
The magnetic field can be thought of as a bar magnet that is tilted 11 degrees from the earth’s spin axis and a magnetic dipole that is positioned at the centre of the earth. The dipole has its South pole pointing towards the geomagnetic North pole, and its North pole pointing towards the geomagnetic South pole. The reason being because the magnet attracts a magnet that has an opposite pole and has the characteristic of repelling a magnet that has the same charge.
Magnetic field density is the unit that shows how strong a magnetic field is. It varies at different positions of the earth. The intensity of the field is lowest near the Equator and greatest near the South and North poles. The field density can be measured in gauss and nanoteslas.
Magnetic fields can vary if disturbed by another magnetic field or from charged particles. The disturbance that the earth mainly receives is from the solar wind(produced by the solar flare on the sun). The solar wind is a stream of charged particles emitted by the Sun that gets trapped in Earth's Van Allen radiation belt, the charged particles can then interact with the Earth’s magnetic field which will then lead to an increased amount of energy entering into the magnetosphere (the earth’s magnetic field deflects the solar wind to form a bounded comet-shaped region surrounding the Earth). The phenomena can only be observed if the amount of charged particles is high enough. If so, it can form magnetic storms which can then lead to blackouts and disruptions in artificial satellites accompanied by the display of the northern lights (it is the natural light can be observed at high latitude).
Earth's dipolar magnetic field Image from: Wikpedia