Untersuchung der Elektrodynamik eines Aurorabogens mit FAST-Satellitendaten und optischen Beobachtungen

The work is devoted to the examination of a wide, stable, wintertime evening arc. Particle and field data measured by the FAST satellite at ~4000km altitude, as well as ground optical data, are used to get a detailed description of the arc electrodynamics. In the vicinity of the arc FAST detected several ion beams, indicating field-aligned potential drop below the satellite, which precludes the mapping of the measured electric field to the ionosphere. In order to derive the ionospheric electric field we introduce a new method, based on the current continuity at ionospheric level and on a parametric arc model. The minimum set of parameters necessary to obtain consistent results includes polarization, a longitudinal electric field constant across the arc, and the coupling between the field-aligned current (FAC) and the electrojet (EJ). The current topology proves to be completely atypical. Although the magnetic field signature suggests the common pattern, with upward and downward FAC sheets connected through Pedersen current, we find that the two current sheets are actually decoupled in the ionosphere. The upward FAC is fed by the westward EJ while most of the downward FAC feeds the eastward EJ. The results point to the prospect of a systematic surveillance of the polar ionosphere by medium altitude satellites, on a spatial scale (~1km) unattainable from ground measurements, and including time intervals when the measured electric field cannot be mapped to the ionosphere. By extending the application of the developed method other peculiar auroral features might be unraveled.Die Arbeit ist der Untersuchung eines breiten, stabilen, Winterabendbogens gewidmet. Teilchen- und Felddaten, vom Satelliten FAST in ~4000km Höhe gemessen, sowie optische Bodenbeobachtungen werden verwendet, um eine detaillierte Beschreibung der Electrodynamik des Bogens zu erhalten. In der Nähe des Bogens wurden mit FAST mehrere Ionenstrahlen entdeckt. Dies weist auf eine parallele Potentialdifferenz unter dem Satelliten hin und schließt damit die mapping des gemessenen elektrischen Feldes zur Ionosphäre aus. Um das ionosphärische elektrische Feld abzuleiten führen wir eine neue Methode ein, die auf der Stromerhaltung auf ionosphärischem Niveau und auf einem parametrischen Bogenmodell basiert. Die minimale Anzahl der Parameter, die notwendig sind übereinstimmende Ergebnisse zu erreichen, umfaßt Polarisation, ein elektrisches Longitudinalfeld das quer durch den Bogen konstant ist und die Kopplung zwischen dem feldparallelen Strom (FAC) und dem Elektrojet (EJ). Die Stromtopologie stellt sich als sehr untypisch heraus. Obwohl die magnetische Feldsignatur das gewöhnliche Muster aufzeigt - sie deutet aufwärts- und abwärtsgerichtete FAC Schichten an, die normalerweise durch den Pedersen Strom verbunden sind - finden wir eigentlich, dass die zwei Stromschichten in der Ionosphäre entkoppelt sind. Das aufwärtsgerichtete FAC wird von dem nach Westen fließenden EJ gespeist, während der größte Teil des abwärtsgerichteten FAC den nach Osten fließenden EJ speist. Die Ergebnisse deuten auf die Möglichkeit einer systematischen Überwachung der polaren Ionosphäre mit Satelliten in mittlere Höhe hin. Dabei kann eine vom Boden aus unerreichbare Auflösung von ~1km erzielt werden. Darüber hinaus können auch Zeiten untersucht werden, in denen eine Projektion des elektrischen Feldes zur Ionosphäre nicht möglich ist. Durch weitere Anwendungen der entwickelten Methode könnte man auch andere bisher nicht erforschte Polarlicht-Phänomene untersuchen

Daedalus Ionospheric Profile Continuation (DIPCont): Monte Carlo studies assessing the quality of in situ measurement extrapolation

In situ satellite exploration of the lower thermosphere-ionosphere system (LTI) as anticipated in the recent Daedalus mission proposal to ESA will be essential to advance the understanding of the interface between the Earth's atmosphere and its space environment. To address physical processes also below perigee, in situ measurements are to be extrapolated using models of the LTI. Motivated by the need for assessing how cost-critical mission elements such as perigee and apogee distances as well as the number of spacecraft affect the accuracy of scientific inference in the LTI, the Daedalus Ionospheric Profile Continuation (DIPCont) project is concerned with the attainable quality of in situ measurement extrapolation for different mission parameters and configurations. This report introduces the methodological framework of the DIPCont approach. Once an LTI model is chosen, ensembles of model parameters are created by means of Monte Carlo simulations using synthetic measurements based on model predictions and relative uncertainties as specified in the Daedalus Report for Assessment. The parameter ensembles give rise to ensembles of model altitude profiles for LTI variables of interest. Extrapolation quality is quantified by statistics derived from the altitude profile ensembles. The vertical extent of meaningful profile continuation is captured by the concept of extrapolation horizons defined as the boundaries of regions where the deviations remain below a prescribed error threshold. To demonstrate the methodology, the initial version of the DIPCont package presented in this paper contains a simplified LTI model with a small number of parameters. As a major source of variability, the pronounced change in temperature across the LTI is captured by self-consistent non-isothermal neutral-density and electron density profiles, constructed from scale height profiles that increase linearly with altitude. The resulting extrapolation horizons are presented for dual-satellite measurements at different inter-spacecraft distances but also for the single-satellite case to compare the two basic mission scenarios under consideration. DIPCont models and procedures are implemented in a collection of Python modules and Jupyter notebooks supplementing this report

What are the fundamental modes of energy transfer and partitioning in the coupled Magnetosphere-Ionosphere system?

The fundamental processes responsible for energy exchange between large-scale electromagnetic fields and plasma are well understood theoretically, but in practice these theories have not been tested. These processes are ubiquitous in all plasmas, especially at the interface between high and low beta plasmas in planetary magnetospheres and other magnetic environments. Although such boundaries pervade the plasma Universe, the processes responsible for the release of the stored magnetic and thermal plasma energy have not been fully identified and the importance of the relative impact of each process is unknown. Despite advances in understanding energy release through the conversion of magnetic to kinetic energy in magnetic reconnection, how the extreme pressures in the regions between stretched and more relaxed field lines in the transition region are balanced and released through adiabatic convection of plasma and fields is still a mystery. Recent theoretical advances and the predictions of large-scale instabilities must be tested. In essence, the processes responsible remain poorly understood and the problem unresolved. The aim of the White Paper submitted to ESA's Voyage 2050 call, and the contents of this paper, is to highlight three outstanding open science questions that are of clear international interest: (i) the interplay of local and global plasma physics processes: (ii) the partitioning during energy conversion between electromagnetic and plasma energy: and (iii) what processes drive the coupling between low and high beta plasmas. We present a discussion of the new measurements and technological advances required from current state-of-the-art, and several candidate mission profiles with which these international high-priority science goals could be significantly advanced.Peer reviewe

Plasma-neutral gas interactions in various space environments: Assessment beyond simplified approximations as a Voyage 2050 theme

In the White Paper, submitted in response to the European Space Agency (ESA) Voyage 2050 Call, we present the importance of advancing our knowledge of plasma-neutral gas interactions, and of deepening our understanding of the partially ionized environments that are ubiquitous in the upper atmospheres of planets and moons, and elsewhere in space. In future space missions, the above task requires addressing the following fundamental questions: (A) How and by how much do plasma-neutral gas interactions influence the re-distribution of externally provided energy to the composing species? (B) How and by how much do plasma-neutral gas interactions contribute toward the growth of heavy complex molecules and biomolecules? Answering these questions is an absolute prerequisite for addressing the long-standing questions of atmospheric escape, the origin of biomolecules, and their role in the evolution of planets, moons, or comets, under the influence of energy sources in the form of electromagnetic and corpuscular radiation, because low-energy ion-neutral cross-sections in space cannot be reproduced quantitatively in laboratories for conditions of satisfying, particularly, (1) low-temperatures, (2) tenuous or strong gradients or layered media, and (3) in low-gravity plasma. Measurements with a minimum core instrument package (< 15 kg) can be used to perform such investigations in many different conditions and should be included in all deep-space missions. These investigations, if specific ranges of background parameters are considered, can also be pursued for Earth, Mars, and Venus

Plasma-neutral interactions in the lower thermosphere-ionosphere : The need for in situ measurements to address focused questions

The lower thermosphere-ionosphere (LTI) is a key transition region between Earth's atmosphere and space. Interactions between ions and neutrals maximize within the LTI and in particular at altitudes from 100 to 200 km, which is the least visited region of the near-Earth environment. The lack of in situ co-temporal and co-spatial measurements of all relevant parameters and their elusiveness to most remote-sensing methods means that the complex interactions between its neutral and charged constituents remain poorly characterized to this date. This lack of measurements, together with the ambiguity in the quantification of key processes in the 100-200 km altitude range affect current modeling efforts to expand atmospheric models upward to include the LTI and limit current space weather prediction capabilities. We present focused questions in the LTI that are related to the complex interactions between its neutral and charged constituents. These questions concern core physical processes that govern the energetics, dynamics, and chemistry of the LTI and need to be addressed as fundamental and long-standing questions in this critically unexplored boundary region. We also outline the range of in situ measurements that are needed to unambiguously quantify key LTI processes within this region, and present elements of an in situ concept based on past proposed mission concepts.Peer reviewe

Lower-thermosphere–ionosphere (LTI) quantities: current status of measuring techniques and models

The lower-thermosphere-ionosphere (LTI) system consists of the upper atmosphere and the lower part of the ionosphere and as such comprises a complex system coupled to both the atmosphere below and space above. The atmospheric part of the LTI is dominated by laws of continuum fluid dynamics and chemistry, while the ionosphere is a plasma system controlled by electromagnetic forces driven by the magnetosphere, the solar wind, as well as the wind dynamo. The LTI is hence a domain controlled by many different physical processes. However, systematic in situ measurements within this region are severely lacking, although the LTI is located only 80 to 200 km above the surface of our planet. This paper reviews the current state of the art in measuring the LTI, either in situ or by several different remote-sensing methods. We begin by outlining the open questions within the LTI requiring high-quality in situ measurements, before reviewing directly observable parameters and their most important derivatives. The motivation for this review has arisen from the recent retention of the Daedalus mission as one among three competing mission candidates within the European Space Agency (ESA) Earth Explorer 10 Programme. However, this paper intends to cover the LTI parameters such that it can be used as a background scientific reference for any mission targeting in situ observations of the LTI.Peer reviewe