The contemporary terrestrial atmosphere loses matter at a rate of around 100,000 tons per year. A major fraction of the net mass loss is constituted by ions, mainly H+ and O+, which escape from the Earth’s ionosphere in the polar regions. Previously, the outflow has only been measured at low altitudes, but to understand what fraction actually escapes and does not return, the measurements should be conducted far from the Earth. However, at large geocentric distances the outflowing ions are difficult to detect with conventional ion instruments on spacecraft, since the spacecraft electrostatic potential normally exceeds the equivalent energy of the ions. This also means that little is known about the ion outflow properties and distribution in space far from the Earth. In this thesis, we present a new method to measure the outflowing low-energy ions in those regions where they previously have been invisible. The method is based on the detection by electric field instruments of the large wake created behind a spacecraft in a flowing, low-energy plasma. Since ions with low energy will create a larger wake, the method is more sensitive to light ions, and our measured outflow is essentially the proton outflow. Applying this new method on data from the Cluster spacecraft, we have been able to make an extensive statistical study of ion outflows from 5 to 19 Earth radii in the magnetotail lobes. We show that cold proton outflows dominate in these large regions of the magnetosphere in both flux and density. Our outflow values of low-energy protons are close to those measured at low altitudes, which confirms that the ionospheric outflows continue far back in the tail and contribute significantly to the magnetospheric content. We also conclude that most of the ions are escaping and not returning, which improves previous estimates of the global outflow. The total loss of protons due to high-latitude escape is found to be on the order of 1026 protons/s.

This thesis addresses solitary waves and their significance for auroral particle acceleration, coronal heating and incoherent scatter radar spectra. Solitary waves are formed due to a balance of nonlinear and dispersive effects. There are several nonlinearities present in ideal magnetohydrodynamics (MHD) and dispersion can be introduced by including theHall termin the generalised Ohm’s law. The resulting system of equations comprise the classical ideal MHD waves, whistlers, drift waves and solitarywave solutions. The latter reside in distinct regions of the phase space spanned by the speed and the angle (to the magnetic field) of the propagating wave. Within each region, qualitatively similar solitary structures are found. In the limit of neglected electron intertia, the solitary wave solutions are confined to two regions of slow and fast waves, respectively. The slow (fast) structures are associated with density compressions (rarefactions) and positive (negative) electric potentials. Such negative potentials are shown to accelerate electrons in the auroral region (solar corona) to tens (hundreds) of keV. The positive electric potentials could accelerate solar wind ions to velocities of 300–800 km/s. The structure widths perpendicular to themagnetic field are in the Earth’s magnetosphere (solar corona) of the order of 1–100 km (m). This thesis also addresses a type of incoherent scatter radar spectra, where the ion line exhibits a spectrally uniform power enhancement with the up- and downshifted shoulder and the spectral region in between enhanced simultaneously and equally. The power enhancements are one order of magnitude above the thermal level and are often localised to an altitude range of less than 20 km at or close to the ionospheric F region peak. The observations are well-described by a model of ion-acoustic solitary waves propagating transversely across the radar beam. Two cases of localised ion line enhancements are shown to occur in conjunction with auroral arcs drifting through the radar beam. The arc passages are associated with large gradients in ion temperature, which are shown to generate sufficiently high velocity shears to give rise to growing Kelvin-Helmholtz (K-H) instabilities. The observed ion line enhancements are interpreted in the light of the low-frequency turbulence associated with these instabilities. / Denna avhandling handlar om solitära vågor och deras roll i norrskensacceleration och koronaupphettning, samt deras signatur i spektra uppmätta med inkoherent spridningsradar. Solitära vågor bildas genom en balans mellan ickelinjära och dispersiva effekter. Ickelinjäriteter finns det gott om i ideal magnetohydrodynamik (MHD) och dispersion kan införas genom att inkludera Halltermen i den generaliserade Ohms lag. Det resulterande ekvationssystemet omfattar de klassiska vågorna inom ideal MHD, visslare, driftvågor och solitära vågor. De sistnämnda återfinns i väldefinierade områden i fasrummet som spänns upp av farten och vinkeln (mot magnetfältet) för den propagerande vågen. Inom varje sådant område återfinns kvalitativt lika solitära våglösningar. Om man försummar elektronernas tröghet begränsas de solitära våglösningarna till två områden med långsamma respektive snabba vågor. De långsamma (snabba) strukturerna är associerade med täthets-kompressioner (förtunningar) och positiva (negativa) elektriska potentialer. De negativa potentialerna visas kunna accelerera elektroner i norrskensområdet (solens korona) till tiotals (hundratals) keV medan de positiva potentialerna accelererar solvindsjoner till hastigheter på 300–800 km/s. Strukturbredderna vinkelrät mot magnetfältet är i jordens magnetosfär (solens korona) av storleksordningen 1–100 km (m). Denna avhandling tar även upp en typ av inkoherent spridningsradarspektra, där jonlinjen uppvisar en spektralt uniform förstärkning. Detta innebär att den upp- och nedskiftade skuldran och spektralbandet däremellan förstärks simultant och i lika hög grad. Effektförstärkningen är en storleksordning över den termiska nivån och är ofta lokaliserad till ett höjd-intervall av mindre än 20 km nära jonosfärens F-skiktstopp. Observationerna beskrivs väl av en modell med solitära vågor som propagerar transversellt genom radarstrålen. Två fall av lokaliserade jonlinjeförstärkningar visas sammanfalla med att norrskensbågar driver genom radarstrålen. I samband med bågarnas passage uppmäts stora gradienter i jontemperatur, vilket visas skapa tillräckligt kraftiga hastighetsskjuvningar för att Kelvin-Helmholtz-instabiliteter ska tillåtas växa. De observerade jonlinjeförstärkningarna tolkas i skenet av den lågfrekventa turbulensen som är kopplad till dessa instabiliteter.