The Magnetosphere’s different elements

Solar Winds and the Bow Shock

Solar winds are made up of streams of charged particles, which are released from the upper atmosphere of the Sun. The winds are a plasma - a soup of disconnected protons, and electrons and other particles - that varies in temperature, direction, and density over time. As the solar winds blow from the Sun, travelling at speeds of 400 to 750 km/s, and they encounter the Earth's magnetic field, where they are heated and slowed. Most, are then deflected around the Earth into the Magnetosheath, forming a bow-shape, much like water is deflected around the bow of a ship, compressing the day-side of the magnetosphere, and drawn out in a long wake on the night-side. The bow shock is estimated to be around 17 kilometres thick, and situated about 90,000 km from Earth.


This is the region inside the bow shock, the zone of 'shocked' solar wind, where Earth's magnetic field changes erratically. Some particles from the solar winds are able to enter this region, but are at a far lower density than outside the bow shock.


This region below the magnetosheath, is classified as the abrupt boundary between the solar wind, and the Earth's magnetic field. The magnetopause contracts inwards and expands outwards in relation to the solar winds changes in pressure.

Plasma Sheet

Some of the solar winds that are able to enter into the magnetosphere, form the plasma sheet. A sheet of hot and charged plasma that extends out into the magnetotail, dividing the north and south 'lobes.'


Despite its' name, as mentioned previously, the Magnetosphere is not a sphere in the spherical sense. The magnetotail is the resulting asymmetric form, generated on the 'downwind' side (or night-side) of the solar winds. The magnetotail extends far beyond the orbit of the moon, and so once a month, for around 6 days, the moon enters the Earth's magnetotail. During the crossing, the plasma sheet, which amongst other particles, contains electrons, gives the moon a negative charge - particularly on the nightside - and is thought to create dust-storms due to an increase in surface voltage. Many of the solar wind particles that have been deflected around the Earth via the bow shock can enter back, into the magnetotail, and stream towards the Earth's magnetic poles. As explained by Brian Cox (2010):

...when the solar wind hits the Earth's magnetic field, it distorts it. It stretches the field out on the night side of the planet... More and more energy goes into the field and over time this energy builds up, stretching the tail until it can no longer hold on to it all. Eventually the energy is released, accelerating a stream of electrically charged particles down the magnetic field lines towards the poles.[1]


This region, contains relatively low energy, cooler, and denser plasma, and is situated above the ionosphere. The plasmasphere is trapped within magnetic field lines, creating an inner 'donut' shaped region, that rotates with the Earth. It is basically an extension of the ionosphere below, and is composed of mainly H+ (hydrogen ions), and a lower amount of ionised helium (less than 20%), flowing out of the ionosphere below.

Van Allen Radiation Belts

These are the zones where solar winds have been captured and held around the Earth. The energetically charged particles create two donut shaped belts - the inner and outer radiation belts. This charged zone deflects further solar winds from entering the Earth's atmosphere. The charged particles are mainly electrons and protons.

The Cusp

The Cusp is the 'open area' between the plasmasphere and radiation belts, where magnetosheath plasma can enter the most directly into the Earth's upper atmosphere. Excited solar wind particles enter through the Earth's magnetosphere somewhere on the frontside (day-side), or, as previously mentioned, back in from the night-side via the magnetotail, and then follow the geomagnetic field lines, which converge to a relatively small area in the high-latitude ionosphere.


[1] Cox, Brian and Andrew Cohen. (2010) 'The Wonders of the Solar System.' Harper Collins Publishers, London, U.K.



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