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Joule heating (JH) in the thermosphere is known to result from the couplingbetween the ionosphere and magnetosphere at high latitudes. A so far relativelyneglected contribution to JH comes from atmospheric motions which, according to magnetic observations, cause electric currents and so constitute a dynamo in a dissipative medium. We present a general theoretical description of the coupling between atmosphere and the ionosphere with a dynamo equationwhere the well-known Pedersen and Hall conductivities appear. The derivation is based on a paper by Parker (1996). A dynamo effect occurs when ∇x(uxB)≠0, where u is the neutral wind and B the magnetic field. The conductivity parallel to B is orders of magnitudes higher than the Pedersen and Hall conductivities. Thus, if uxB is varying along magnetic field lines, then dissipative dynamo currents develop. For example, at gravity waves generally uxB varies along magnetic field lines, and so dynamo effects are produced when they propagate into the dynamo regions of the lower thermosphere.We estimate that the tidal Sq dynamo globally dissipates roughly a power of 2 GW quasi-permanently. But also the electrodynamic dissipation by medium and small scale gravity waves propagating from the mesosphere into the lower thermosphere could be a significant source of heat. Unlike the current systems coupling the magnetosphere and ionosphere which are observed by satellites like Swarm, the currents of a gravity wave dynamo are confined to the lower thermosphere and can only be observed with a very low orbiting satellite or sounding rockets., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

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.

We present Swarm satellite and EISCAT radar observations of electrodynamical parameters in the midnight sector at high latitudes. The most striking feature is a plasma flow channel located equatorward of the polar cap boundary within the dawn convection cell. The flow channel is 1.5° wide in latitude and contains southward electric field of 150 mV/m, corresponding to eastward plasma velocities of 3,300 m/s in the F‐region ionosphere. The theoretically computed ion temperature enhancement produced by the observed ion velocity is in accordance with the measured one by the EISCAT radar. The total width of the auroral oval is about 10° in latitude. While the poleward part is electric field dominant with low conductivity and the flow channel, the equatorward part is conductivity dominant with at least five auroral arcs. The main part of the westward electrojet flows in the conductivity dominant part, but it extends to the electric field dominant part. According to Kamide and Kokubun (1996), the whole midnight sector westward electrojet is expected to be conductivity dominant, so the studied event challenges the traditional view. The flow channel is observed after substorm onset. We suggest that the observed flow channel, which is associated with a 13‐kV horizontal potential difference, accommodates increased nightside plasma flows during the substorm expansion phase as a result of reconnection in the near‐Earth magnetotail.

In this article we use Cluster power density (E . J) data from 2001, 2002, and 2004 to investigate energy conversion and transfer in the plasma sheet. We show that a southward IMF B-z is favorable for plasma sheet energy conversion, and that there is an increased particle and Poynting flux toward the Earth at times when Cluster observes an enhanced energy conversion in the plasma sheet. Conversion from electromagnetic to kinetic energy is increasingly dominant farther down-tail, while the generation of electromagnetic power from kinetic energy becomes important toward the Earth with a maximum at roughly 10 R-E. By linking observations of the key quantity E . J to observations of the solar wind input and earthward energy flux, our results demonstrate the role of the inner tail to midtail plasma sheet as a mediator between the solar wind energy input into the magnetosphere and the auroral dissipation in the ionosphere.

International audience; We present observations from three Cassini flybys of Titan using data from the radio and plasma wave science, magnetometer and plasma spectrometer instruments. We combine magnetic field and cold plasma measurements with calculated conductivities and conclude that there are currents of the order of 10 to 100 nA m−2 flowing in the ionosphere of Titan. The currents below the exobase (∼1400 km) are principally field parallel and Hall in nature, while the Pedersen current is negligible in comparison. Associated with the currents are perpendicular electric fields ranging from 0.5 to 3 μV m−1.

We present Cluster measurements of large electric fields correlated with intense downward field-aligned currents, and show that the data can be reproduced by a simple model of ionospheric plasma depletion caused by the currents. This type of magnetosphere-ionosphere interaction may be important when considering the mapping between these two regions of space.

International audience; The extremely large solar eruption on 28 October 2003 caused an intense geomagnetic storm at Earth. A second solar eruption on 29 October resulted in a reintensification of the storm about a day later. Similarities and differences between these two events in terms of solar eruption, solar wind driver, and their resulting effect on the near-Earth environment are investigated and put into context of previous works on storm geoeffectivness. Within the second storm some of the strongest substorms in the history of magnetic recordings occurred in northern Scandinavia. The aim of this study is to investigate the cause and resulting effects of these extreme geomagnetic disturbances on the ionosphere and upper atmosphere, focusing on the northern Scandinavian sector where these disturbances reached extremely high values. During this time period, well after the initial arrival of the Interplanetary Coronal Mass Ejection (ICME), the Cluster spacecraft were located at the flank of the magnetospheric tail. The satellites were passed several times by an inward and consecutively outward moving magnetopause in close relation to the substorm intensifications in northern Scandinavia. We propose that the evolution of these magnetospheric substorm intensifications are influenced by the changing dynamics of the solar wind in the form of increased pressure occurring after a prolonged period of southward Interplanetary Magnetic Field (IMF) and thus excessive energy loading into the magnetosphere prior to the onset of the intensifications. We present evidence of external pressure pulse triggering and possibly also quenching of these substorm onsets and recoveries. In addition, EISCAT data have been used to investigate the detailed local behavior of the ionospheric plasma, giving rise to such extreme disturbances. We found that in this case, extreme combinations of enhanced conductivity and intense electric field resulted in very high current intensities (westward electrojet ∼7.4 MA) and very fast onset of such currents. The inline equation associated geomagnetically induced currents caused power failures in southern Sweden.

Intense high-latitude electric fields (>150 mV/m mapped to ionospheric altitude) at 4?7 RE geocentric distance have been investigated in a statistical study, using data from the Cluster satellites. The orbit of the Cluster satellites limits the data collection at these altitudes to high latitudes, including the poleward part of the auroral oval. The occurrence and distribution of the selected events have been used to characterize the intense electric fields and to investigate their dependance on parameters such as MLT, CGLat, altitude, and also Kp. Peaks in the local time distribution are found in the evening to morning sectors but also in the noon sector, corresponding to cusp events. The electric field intensities decrease with increasing latitude in the region investigated (above 60 CGLat). A dependence on geomagnetic activity is indicated since the probability of finding an event increases up to Kp=5?6. The scales sizes are in the range up to 10 km (mapped to ionospheric altitude) with a maximum around 4?5km, consistent with earlier findings at lower altitudes and Cluster event studies. The magnitudes of the electric fields are inversely proportional to the scale sizes. The type of electric field structure (convergent or divergent) is consistent with the FAC direction for a subset of events with electric field intensities in the range 500?1000 mV/m and with clear bipolar signatures. The FAC directions are also consistent with the Region 1 and NBZ current systems, the latter of which prevail only during northward IMF conditions. For scale sizes less than 2 km the majority of the events were divergent electric field structures. Both converging and diverging electric fields were found throughout the investigated altitude range (4?7 RE geocentric distance). Keywords. Magnetospheric physics (Electric fields; Auroral phenomena; Magnetosphere-ionosphere interactions)

We present observations of wave activity associated with thin current sheets at the magnetopause, with main emphasis on two frequency ranges: lower hybrid/whistler and Langmuir/upper hybrid. We use multipoint measurements by the Cluster spacecraft to identify spatial properties of the waves. Most of the wave activity is concentrated on the edges of the current sheets. Langmuir/upper hybrid waves are usually observed in association with parallel currents and are generated by the electron beams carrying these currents. We also find that the appearance of lower hybrid and whistler waves depends on the value of plasma beta outside the current sheet, with no lower hybrid waves observed for high values of beta (∼ 10). We discuss mechanisms for generation of these waves, and possible relation of the observed phenomena to reconnection at the magnetopause.

Giant pulsations are nearly monochromatic ULF-pulsations of the Earth's magnetic field with periods of about 100 s and amplitudes of up to 40 nT. For one such event ground-magnetic observations as well as simultaneous GEOS-2 magnetic and electric field data and proton flux measurements made in the geostationary orbit have been analysed. The observations of the electromagnetic field indicate the excitation of an odd-mode type fundamental field line oscillation. A clear correlation between variations of the proton flux in the energy range 30-90 keV with the giant pulsation event observed at the ground is found. Furthermore, the proton phase space density exhibits a bump-on-the-tail signature at about 60 keV. Assuming a drift-bounce resonance instability as a possible generation mechanism, the azimuthal wave number of the pulsation wave field may be determined using a generalized resonance condition. The value determined in this way, m = - 21 ± 4, is in accord with the value m = - 27 ± 6 determined from ground-magnetic measurements. A more detailed examination of the observed ring current plasma distribution function f shows that odd-mode type eigenoscillations are expected for the case ∂f / ∂W > 0, much as observed. This result is different from previous theoretical studies as we not only consider local gradients of the distribution function in real space, but also in velocity space. It is therefore concluded that the observed giant pulsation is the result of a drift-bounce resonance instability of the ring current plasma coupling to an odd-mode fundamental standing wave. The generation of the bump-on-the-tail distribution causing ∂f / ∂W > 0 can be explained due to velocity dispersion of protons injected into the ring current. Both this velocity dispersion and the necessary substorm activity causing the injection of protons into the nightside magnetosphere are observed.Key words. Magnetospheric physics (energetic particles , trapped; MHD waves and instabilities) · Space plasma physics (wave-particle interactions).

資料番号: PAIS08271000

Plasma convection in the high-latitude ionosphere provides important information about magnetosphere-ionosphere-thermosphere coupling. In this study we estimate the along-track component of plasma convection within and around the polar cap, using electron density profiles measured by the three Swarm satellites. The velocity values estimated from the two different satellite pairs agree with each other. In both hemispheres the estimated velocity is generally anti-sunward, especially for higher speeds. The obtained velocity is in qualitative agreement with Super Dual Auroral Radar Network data. Our method can supplement currently available instruments for ionospheric plasma velocity measurements, especially in cases where these traditional instruments suffer from their inherent limitations. Also, the method can be generalized to other satellite constellations carrying electron density probes., Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe, 503