![]() To first order, the dynamic pressure dominates the plasma behind the bow shock in a region referred to as the magnetosheath, whereas the magnetic pressure dominates inside Earth's magnetosphere. The magnetopause is the location where the solar wind total pressure, modified by Earth's bow shock, is balanced by the pressure inside the magnetosphere. The two main loci of reconnection are the magnetopause in the day side and the magnetotail in the night side. The magnetic field lines undergo a series of reconnection and convection events that were first described by Dungey ( Dungey, 1961). When the IMF has a component antiparallel to Earth's magnetic field, i.e., when the IMF has a southward component in the geocentric solar magnetospheric coordinate system, reconnection can occur on the day side of Earth's magnetosphere. The dusk-to-dawn distribution of the equipotential is affected by the direction of the y component of the IMF. Both the Standard Magnetic Reconnection (SMR) and the PTE are easier to understand if the x and y components are assumed to vanish. (1994) have shown that similar conditions are held until the IMF reaches to 60 degrees northward. A strictly southward IMF, B(0, 0, − B z), although rare in practice, is worth special attention since it is conducive to geomagnetic activity. This situation is associated with a dawn-dusk electric field within the plasma sheet, the earthward convection of PS plasma, and the energization of plasma sheet particles. When the IMF has a southward component, the high-latitude ionospheric convection pattern shows a familiar two-cell geometry: antisunward flow at highest latitudes, sunward flow at lower latitudes, both on the dawn and dusk sides. Wayne Keith, Walter Heikkila, in Earth's Magnetosphere (Second Edition), 2021 1.15.1 Polar cap during southward IMF However, the Sun is a relatively small and inactive star other stars can have quite different and often far more intense winds. If the Sun undergoes a catastrophic collapse to form a white dwarf then there may be one or several episodes of impulsive mass ejection called novae. Later in its life the Sun will go through a red giant phase, expanding outward to envelop the Earth, and the wind may again become quite strong. The Sun probably had a very vigorous wind early in its life when the solar convection zone extended throughout the entire volume of the Sun. However, the Sun changes over its life, as do all stars. Presently the solar wind carries away only a very small amount of mass from the Sun – so small that if assumed the same for 4.5 billion years it would have removed only ∼0.01% of the total mass of the Sun. Calculations of the angular momentum transfer suggest that the present-day solar wind and IMF could easily have doubled the rotation period of the Sun, from 12.25 to 25.5 days, over the 4.5 billion year life of the Sun. However, over the life of the Sun, the effect can be important. Generally this is a small effect, with the corotation distance being 10–20 R S at most, or 0.1 AU. In doing this, the IMF causes angular momentum of the Sun to be transferred to the solar wind. Because it is attached to the Sun, and has a small, but finite strength, the IMF tends to cause the solar wind to rotate with the Sun out to some distance above the photosphere. The IMF is not completely passive in the solar wind. Tsurutani, in Encyclopedia of Atmospheric Sciences (Second Edition), 2015 The Solar Wind over the Life of the Sun
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