Spatio-temporal fluctuations are also known to render the magnetopause semi-permeable, so that some magnetosheath plasma can cross it, thus forming the magnetospheric boundary layer. One of the effects of the continuous minor fluctuations in solar wind dynamic pressure is the oscillating motion of the magnetopause. Rather, it is constantly in motion, as the orientation of the Earth's magnetic dipole varies with the Earth's daily rotation and with its yearly revolution around the Sun, and as the solar wind is characterized by a strong time-variability on time scales ranging from seconds to years.Īs a consequence of this time-variability, the sizes and shapes of the regions may change with time.įor instance, when material from a solar coronal eruption (a so-called coronal mass ejection) travels through the interplanetary medium and hits the Earth, the dynamic pressure of the solar wind is strongly enhanced so that the bow shock and the magnetopause are pushed inward, producing a magnetospheric storm.
The magnetosphere is not a static structure. Note the particular cusp regions above the magnetic poles these are regions where solar wind can enter relatively easily into the magnetosphere. The length of the tail is hundreds of R_E. The subsolar point, also known informally as the “nose'' of the magnetopause, is normally situated at an upstream stand-off distance of about 10 R_E (Earth radii), while the bow shock stand-off distance is typically 15 R_E. The magnetopause has a shape that is elongated and stretched out in the antisolar direction, forming a long magnetotail, which is in a sense similar to the wake behind the boat. The impermeable outer surface of the magnetosphere, where the total pressure (the sum of the ram pressure and the thermal and the magnetic pressures) of the compressed solar wind precisely balances the total pressure inside the magnetosphere, is called the magnetopause. Magnetopause, the impermeable outer surface The solar wind in the magnetosheath, the region between the bow shock and the Earth's magnetosphere, is forced to flow around the Earth's magnetosphere and is compressed. Magnetosheath, where the solar wind is compressedĪ bow shock is formed in front of the Earth's magnetosphere, demarcating the region where the solar wind flow is affected by the presence of the Earth.Īt the bow shock the supersonic solar wind is slowed down and becomes subsonic. It is pervaded by the interplanetary magnetic field. The solar wind consists of particles that are mainly of solar origin.
The solar wind -magnetosphere interaction is very similar to the flow of water around the boat. The water behind the bow wave is forced to flow smoothly around the boat's hull. In front of the boat a bow wave is formed: that bow wave demarcates the region in which the boat disturbs the flow of the water.
Consider a boat that moves through the sea. The nature of the boundary of the magnetosphere is illustrated by the following analogy. The magnetosphere can be defined as the space filled primarily with particles from terrestrial origin. The complex structure of the magnetosphere is the result of the interplay between the charged particles originating in the upper layers of the terrestrial atmosphere, whose motion is guided by the Earth's magnetic field, and the solar wind particles carrying the interplanetary magnetic field.
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