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The behaviour of ions in space and an atmosphere is determined by a balance of many different factors: ionisation, interaction with neutrals, and the integrated effect of electric and magnetic fields over a much larger size and time scale than that of electrons. This causes the ion behaviour to be quite different from the electron behaviour in the solar wind-magnetosphere-ionosphere interactions and magnetospheric dynamics. The less coherence with local fields for ion behaviour than electron behaviour, together with the complication of different masses of different ions, make ion phenomena difficult to analyze, and hence many ion phenomena are remained poorly understood. This lecture overviews some of these ion phenomena with particular stress on relatively less investigated areas.* Ion injection phenomena in the dayside magnetosphere: cusp, transient injections, returning ionospheric ions, as constrainer but not carrier of large-scale electric current. * Ion escape to space: destination, amount, oxidation effect, consequence of atmospheric evolution, active role in energy extraction from the solar wind.* Inner magnetospheric ions: multiple sources of structured sub-keV ions, relation to substorm electric field, modulation by Pc5 waves, unexpected mass-dependency, relation to aurora.* Exospheric origin cold ions: variable production in both space and time, influence on bow shock and foreshock, resultant Mars-Venus-Earth difference.* Space weather and substorm: shortest propagation path, effect on the ionosphere, long term trend, and few-min local forecast.* Ions by ionising radiation from nuclear accidents: new monitoring method. [ABSTRACT FROM AUTHOR]

Recent in-situ studies suggest that ion and neutral escapes have substantially affected the evolution of the atmosphere and life. To examine this problem, we need a dedicated mission. One example is ESCAPE (\url{http://cluster.irap.omp.eu/public/ESCAPE/ESCAPE\%5fM5\%5fProposal\%5fV1.1.pdf}) targeting comprehensive understanding of both ion escape and neutral escape, with as much cost as 400 Meur. \newline\newline Size and cost of the mission can be reduced significantly by limiting our target, e.g., to the total ion escape rate, during very active solar/geomagnetic conditions, which are the most relevant from the atmospheric evolution viewpoint for the present Earth. By limiting measurements to ions, the Sun-Earth Lagrange L2 point becomes an ideal place because a semi-stable Lissajous/Halo orbit around L2 rather than orbiting the Earth allows to quickly explore the 2D cross-section of the tail magnetosphere, through which all escaping ions will flow after picked up by the solar wind. \newline\newline One advantage of the Sun-Earth L2 is that we expect good piggyback opportunities, because L2 is a favorite place for large space observatories (e.g., ESA's Herschel, Gaia, and Euclid) that require relatively large launchers. The resulting large piggyback capabilities at L2 are not useful for Earth observation or commercial purposes, allowing extra science missions as piggyback. In fact, ESA recently announced a science mission opportunity of nearly one ton starting from L2 as piggyback of PLATO or ARIEL missions. \newline\newline The size of a piggyback L2 mission for ion escape measurements can range from a formation of one mother plus two daughter spacecraft (Far Tail Explore: FATE) down to a single cubesat mission. The cubesat/daughter is equipped with two ion instruments (MCP-type for 0.1-20 keV and SSD-type for 15-85 keV that can cover picked-up O$^+$ up to 1000 km/s) and minimum additional supportive payload (magnetometer and/or Langmuir probe), costing less than 10 Meur including instrument and launch. In the FATE mission (\url{http://www..irf.se/\%7Eyamau/future/f1/Fate\%5fphase1\%5ffinal.pdf}) that we proposed for ESA's A/O, the mother spacecraft has more complete particle and supportive packages. \newline\newline With FATE instrumentation, it is possible (1) to obtain the total ion escape (flux, active cross-section, and composition) from the Earth and its variability at the ultimate downstream, (2) to identify the relative importance of the different ion escape routes and mixing of different plasmas far downstream, (3) to monitor interplanetary shocks / solar energetic particles (SEP) at the Earth and L2 for more accurate space weather warning, (4) to study fine-scale magnetospheric boundary far downstream where all boundary-related instabilities are well developed including folding including transient interactions with SEP. [ABSTRACT FROM AUTHOR]

The evolution of the Earth's atmosphere cannot be understood without an assessment of the amount of atmospheric escape to space. While the current neutral escape from the Earth's atmosphere is considered negligible (at least for the heavier species), the ion escape is more difficult to evaluate because of the diversity of escape mechanisms and the complexity of ion escape routes, and the possible recirculation of the plasma. Tracking the heavy ions is therefore of paramount importance. It is difficult to assess the total ion escape rate based on measurements in near-Earth space, in particular because the net escape rate is the difference between the upward ion flux and the downward flux of recirculated plasma. Both the upward and downward contributions are characterized by a strong spatial and time variability and a dependence on solar and geomagnetic conditions.It was recently proposed to measure the net outflow rate from a vantage point in the deep tail (ESA F1 FATE mission proposal). It is reasonable to assume that the return flow from beyond ~200 RE is negligible, so that an evaluation of the net escape rate becomes more straightforward. A contribution that would be missed are ions that are transformed into escaping energetic neutral atoms through charge exchange. Ions that are lost through magnetopause shadowing will be dragged along with the magnetosheath flow and can still be detected in the magnetosheath adjacent to the tail magnetopause, except if they are too energetic. Using simulations based on a simplified model, we examine whether it is possible to disentangle the contributions from the different atmospheric escape processes from their combined signatures in the deep tail. [ABSTRACT FROM AUTHOR]