Abstract
AbstractIonospheric ions (mainly H+, He+, and O+) escape from the ionosphere and populate the Earth's magnetosphere. Their thermal energies are usually low when they first escape the ionosphere, typically a few electron volt to tens of electron volt, but they are energized in their journey through the magnetosphere. The ionospheric population is variable, and it makes significant contributions to the magnetospheric mass density in key regions where magnetic reconnection is at work. Solar wind—magnetosphere coupling occurs primarily via magnetic reconnection, a key plasma process that enables transfer of mass and energy into the near‐Earth space environment. Reconnection leads to the triggering of magnetospheric storms, auroras, energetic particle precipitation and a host of other magnetospheric phenomena. Several works in the last decades have attempted to statistically quantify the amount of ionospheric plasma supplied to the magnetosphere, including the two key regions where magnetic reconnection occurs: the dayside magnetopause and the magnetotail. Recent in situ observations by the Magnetospheric Multiscale spacecraft and associated modeling have advanced our current understanding of how ionospheric ions alter the magnetic reconnection process, including its onset and efficiency. This article compiles the current understanding of the ionospheric plasma supply to the magnetosphere. It reviews both the quantification of these sources and their effects on the process of magnetic reconnection. It also provides a global description of how the ionospheric ion contribution modifies the way the solar wind couples to the Earth's magnetosphere and how these ions modify the global dynamics of the near‐Earth space environment.
Highlights
Magnetospheric plasma composition and circulation, as well as the sources and sinks of plasma populations in the magnetosphere, have been extensively studied since the beginning of the space era in the late 1950s
Satellite observations made in the 1970s through the 2000s, for example, the International Sun-Earth Explorer (ISEE), Dynamics Explorer (DE), Polar, and Cluster missions, measured the characteristics of a plasma population extending from the nightside through dawn up to the noon sector outside of the plasmasphere that appeared unrelated to the known magnetospheric plasma populations in the radiation belts, plasmasphere, magnetotail plasma sheet, and inner magnetospheric ring current
All these findings indicate that the presence of cold ions modifies the energy partition that is converted from the fields into particle kinetic energy by magnetic reconnection, quantification of the energy taken by cold ions in the form of bulk kinetic acceleration and heating from a statistical perspective remains unknown
Summary
Magnetospheric plasma composition and circulation, as well as the sources and sinks of plasma populations in the magnetosphere, have been extensively studied since the beginning of the space era in the late 1950s. Using various direct and indirect techniques, past and recent studies have demonstrated that these particles are important to the dynamics of the Earth's magnetosphere. These particles, H+, along with heavy ions species such as O+ and He+, often dominate the magnetospheric mass-density. We focus on the two main regions where magnetic reconnection plays a major role: the dayside magnetopause and the Earth's magnetotail.
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