Search

In magnetized plasmas such as the ionosphere, electric currents develop in regions of strong density gradients to balance the resulting plasma pressure gradients. These currents, usually known as diamagnetic currents decrease the magnetic pressure where the plasma pressure increases, and vice versa. In the low‐latitude ionosphere, equatorial plasma depletions (EPDs) are well known for their steep plasma density gradients and adverse effect on radio wave propagation. In this paper, we use continuous measurements of the magnetic field and electron density from the European Space Agency's Swarm constellation mission to assess the balance between plasma and magnetic pressure across large‐scale EPDs. The analysis is based on the magnetic fluctuations related to diamagnetic currents flowing at the edges of EPDs. This study shows that most of the EPDs detected by Swarm present a decrease of the plasma pressure relative to the ambient plasma. However, EPDs with high plasma pressure are also identified mainly in the vicinity of the South Atlantic magnetic anomaly. From the electron density measurements, we deduce that such an increase in plasma pressure within EPDs might be possible by temperatures inside the EPD as high as twice the temperature of the ambient plasma. Due to the distinct location of the high‐pressure EPDs, we suggest that a possible heating mechanism might be due to precipitation of particle from the radiation belts. This finding corresponds to the first observational evidence of plasma pressure enhancements in regions of depleted plasma density in the ionosphere. First observational evidence of high plasma pressure in depleted density regions in the ionosphereHigh‐pressure plasma depletions are suggested to exhibit temperatures at least twice the backgroundParticle precipitation is a likely heating source due to the longitudinal distribution of the events

We investigate the statistical, dual‐spacecraft correlations of field‐aligned current (FAC) signatures between two Swarm spacecraft. For the first time, we infer the orientations of the current sheets of FACs by directly using the maximum correlations obtained from sliding data segments. The current sheet orientations are shown to broadly follow the mean shape of the auroral boundary for the lower latitudes and that these are most well ordered on the dusk side. Orientations at higher latitudes are less well ordered. In addition, the maximum correlation coefficients are explored as a function of magnetic local time and in terms of either the time shift (δt) or the shift in longitude (δlon) between Swarms A and C for various filtering levels and choice of auroral region. We find that the low‐latitude FACs show the strongest correlations for a broad range of magnetic local time centered on dawn and dusk, with a higher correlation coefficient on the dusk side and lower correlations near noon and midnight. The positions of maximum correlation are sensitive to the level of low‐pass filter applied to the data, implying temporal influence in the data. This study clearly reflects the two different domains of FACs: small‐scale (some tens of kilometers), which are time variable, and large‐scale (>50 km), which are rather stationary. The methodology is deliberately chosen to highlight the locations of small‐scale influences that are generally variable in both time and space. We may fortuitously find a potential new way to recognize bursts of irregular pulsations (Pi1B) using low‐Earth orbit satellites. For the first time, we infer the orientations of the current sheets of FACs using a maximum correlation methodThis study clearly reflects two different domains of FACs: small‐scale, which are time variable, and large‐scale, which are rather stationaryWe find a potential new way to recognize bursts of irregular pulsations (Pi1B) using low‐earth orbit satellites

The lower atmospheric forcing effects on the ionosphere are particularly evident during extreme meteorological events known as sudden stratospheric warmings (SSWs). During SSWs, the polar stratosphere and ionosphere, two distant atmospheric regions, are coupled through the SSW‐induced modulation of atmospheric migrating and nonmigrating tides. The changes in the migrating semidiurnal solar and lunar tides are the major source of ionospheric variabilities during SSWs. In this study, we use 55 years of ground‐magnetometer observations to investigate the composite characteristics of the lunar tide of the equatorial electrojet (EEJ) during SSWs. These long‐term observations allow us to capture the EEJ lunar tidal response to the SSWs in a statistical sense. Further, we examine the influence of solar flux conditions and the phases of quasi‐biennial oscillation (QBO) on the lunar tide and find that the QBO phases and solar flux conditions modulate the EEJ lunar tidal response during SSWs in a similar way as they modulate the wintertime Arctic polar vortex. This work provides first evidence of modulation of the EEJ lunar tide due to QBO. This study focuses on the vertical coupling between the polar stratosphere and equatorial ionosphere during sudden stratospheric warmings (SSWs). Extreme meteorological events such as SSWs induce variabilities in the ionosphere by modulating the atmospheric migrating and nonmigrating tides, and these variabilities can be comparable to a moderate geomagnetic storm. Observations and modeling studies have found that the changes in the migrating semidiurnal solar and lunar tides are a major source of ionospheric variabilities during SSWs. The equatorial electrojet (EEJ) is a narrow ribbon of current flowing over the dip equator in the ionosphere and is particularly sensitive to tidal changes. Long‐term ground‐magnetometer recordings have been used in this study to estimate the variations induced in EEJ during SSWs due to the lunar semidiurnal tide in a statistical sense. The wintertime Arctic polar vortex and the occurrence of SSWs are modulated by solar flux conditions and the phases of quasi‐biennial oscillation. In this work, we find the first evidence of lunar tidal modulation of EEJ due to quasi‐biennial oscillation during SSWs. Our findings will be useful in providing improved predictions of ionospheric variations due to SSWs. The aeronomy community will be the most impacted by this paper. Lunar tide of the equatorial electrojet during SSWs has been studied using composite analysisLarger lunar tidal enhancements are observed during vortex‐split SSWs than vortex‐displaced SSWsEvidence of modulation of lunar tide by the QBO phase is seen during SSWs

This paper presents a quantitative assessment of high-latitude energy input and its partitioning in the polar cap by synthesizing various space and ground-based observations during the 17 January 2005 geomagnetic storm. It was found that Joule heating is the primary form of magnetospheric energy input, especially during active times when the hemispheric-integrated Joule heating can be an order of magnitude larger than the hemispheric-integrated auroral power. Most of magnetospheric energy is dissipated in the auroral zone rather than in the polar cap. On average, only about 22–25% of the total hemispheric energy input is dissipated into the polar cap region bordered by the convection reversal boundary (CRB) and the poleward auroral flux boundary (FXB). The impact of high-latitude energy input was also investigated to unveil the causal relationship between Joule heating and the formation of polar cap mass density anomalies. Our numerical simulation demonstrated that thermosphere dynamics readily redistributes composition, temperature, and mass through upwelling and atmospheric gravity waves. The polar cap mass density anomalies observed by the CHAMP satellite during the storm were largely a result of large-scale atmospheric gravity waves. Therefore, an increase in local thermospheric mass density does not necessarily mean there is direct energy input. The polar cap is not the primary location of high-latitude energy inputThermospheric mass density anomalies do not always coincide with direct local energy dissipationThermosphere dynamics redistributes mass globally through gradient-wave adjustment

We present multimission observations of field‐aligned currents, auroral oval, and magnetopause crossings during the 17 March 2015 magnetic storm. Dayside reconnection is expected to transport magnetic flux, strengthen field‐aligned currents, lead to polar cap expansion and magnetopause erosion. Our multimission observations assemble evidence for all these manifestations. After a prolonged period of strongly southward interplanetary magnetic field, Swarm and AMPERE observe significant intensification of field‐aligned currents. The dayside auroral oval, as seen by DMSP, appears as a thin arc associated with ongoing dayside reconnection. Both the field‐aligned currents and the auroral arc move equatorward reaching as low as ~60° magnetic latitude. Strong magnetopause erosion is evident in the in situ measurements of the magnetopause crossings by GOES 13/15 and MMS. The coordinated Swarm, AMPERE, DMSP, MMS and GOES observations, with both global and in situ coverage of the key regions, provide a clear demonstration of the effects of dayside reconnection on the entire magnetosphere. Observed manifestations of dayside reconnection on field‐aligned currents and auroral ovalObserved strong magnetopause erosion during storm main phaseDemonstrated effects of dayside reconnection on entire magnetosphere

We show for the first time, with direct, multispacecraft calculations of electric current density, and other methods, matched signatures of field‐aligned currents (FACs) sampled simultaneously near the ionosphere at low (~500 km altitude) orbit and in the magnetosphere at medium (~2.5 REaltitude) orbits using a particular Swarm and Cluster conjunction. The Cluster signatures are interpreted and ordered through joint mapping of the ground/magnetospheric footprints and estimation of the auroral zone boundaries (taken as indication of the boundaries of Region 1 and Region 2 currents). We find clear evidence of both small‐scale and large‐scale FACs and clear matching of the behavior and structure of the large‐scale currents at both Cluster and Swarm. The methodology is made possible through the joint operations of Cluster and Swarm, which contain, in the first several months of Swarm operations, a number of close three‐spacecraft configurations. Gives correlated FAC signatures between low (~500 km) and high (~4 RE) altitudesResolves large‐ and small‐scale structures at low altitudeConfirms the scaling of current strength at each location

Stochastic dust charge fluctuations have been studied in the light of Cassini data on the near‐Enceladus plasma environment. Estimates of fluctuation time scales showed that this process can be of importance for the grains emanating from the icy moon. The analytical modeling predicts that in the dust‐loaded Enceladus plasma a majority of the grains acquires fluctuating negative charges, but there might appear a minority of positively charged particles. The probability of this effect mostly depends on the ratio of the dust/plasma number densities. Our findings appear to be supported by the available Cassini Plasma Spectrometer measurements of the charged grain distributions during E3 and E5 plume flybys. The theoretical results can also provide new insights into the intricate process of particle dynamics in the inner magnetosphere. Stochastic dust charge fluctuations are studied in the light of Cassini dataModeling predicts coexistence of negative/positive fluctuating dust chargesResults might explain the available CAPS measurements

We use ground‐based and satellite measurements to examine, for the first time, the characteristics of equatorial electrodynamic perturbations measured during the 2002 major and 2010 minor Southern Hemisphere sudden stratospheric warming (SSW) events. Our data suggest the occurrence of enhanced quasi 2 day fluctuations during the 2002 early autumnal equinoctial warming. They also show a moderately large multi‐day perturbation pattern, resembling those during arctic SSW events, during 2002 late equinox, as the major SSW was weakening. We also compare these data with extensive recent results that showed the fundamentally important role of lunar semidiurnal tidal effects on low latitude electrodynamic perturbations during arctic SSW events.

Abstract: Using time-dependent 3D tomography method, the electron density distributions in the low-latitude ionosphere during November 2004 super-storm are reconstructed from GPS observations of joint ground-based IGS network and onboard CHAMP/GRACE satellites. The reconstructed electron densities are validated by satellite in situ measurements of CHAMP and GRACE satellites. It is indicated by computer tomography (CT) reconstructions that the long-lived positive storm phase during the first main phase of the storm (November 8) is mainly attributed to enhancement of electron density in the upper F region above the F2 peak. It is found by the CT imaging that the top-hat-like F2-3 double layers occurred in the equatorial ionization anomaly region during the main phase of the storm (at forenoon of November 8). The structures of column-like enhanced electron density are found at the time near the minimum of Dst and in the longitudinal sector about 157°E, which extend from the topside ionosphere toward plasmasphere, reaching at least about 2000 km as high. Their footprints stand on the two peaks of the EIA.

This study investigates two substorm onset events with favorable constellations of spacecraft, TC-1 and Cluster, separated by several Earth radii. The substorms have been identified in both auroral regions. One is believed to be triggered by a northward turning of the interplanetary magnetic field (IMF), while the other occurs under generally southward IMF. For both events, Cluster was located tailward of TC-1, but observed the dipolarization at earlier time for one event while at later time for the other. The timing difference of dipolarization at different positions could be explained by the earthward or tailward propagation of the field disturbances in the radial direction. The earthward dipolarization front was found in one case to bounce back and forth at TC-1. The earthward propagation was accompanied by a fast earthward plasma flow for the 21 September 2005 event. The event analysis suggests that substorms can be quite different from case to case due to differences in the solar wind condition and magnetotail configuration.

The total solar eclipse of August 11, 1999 offered a unique opportunity for the study of its geomagnetic effect — more specifically, of its effect on geomagnetic (Pc3) pulsations, as it swept through Europes many observatories, and additional temporary stations have also been established by Japanese, German and Hungarian groups. The present paper starts with an analysis of the ionospheric-interplanetary background. In the interplanetary medium, no indication was found which could result in any extraordinary event in pulsation activity. The both horizontally and vertically widespread ionospheric effect (electron density decrease) explains a change of the polarisation angle by about ten degrees in the local field line resonance (FLR) band. However, the most significant solar eclipse effect was identified as dramatic clockwise rotation (up to 70 degrees) of the polarisation ellipse of Pc3, Pc4 and Pc5 pulsations. Pulsation data exhibit a strong amplitude decrease (roughly by a factor of two) in and around the totality spot of the eclipse. The decrease is most significant at the local field line resonance (FLR) period. In the actual case, the FLR decrease swept over Europe with a speed being similar to the speed of the dark spot. We suppose that the FLR mechanism was disturbed by the change of particle distribution along the field lines ending in the dark zone due to upward propagation of the electron density decrease caused by the lack of ionising solar radiation in the E-layer of the ionosphere. Thus, the FLR mechanism can be disturbed both from outside, by a sudden change of the interplanetary magnetic field (Verő et al. 1998) and from inside, by a change of the particle density/distribution along the actual field line.

Conducting ocean water, as it flows through the Earth’s magnetic field, generates secondary electric and magnetic fields. An assessment of the ocean-generated magnetic fields and their detectability may be of importance for geomagnetism and oceanography. Motivated by the clear identification of ocean tidal signatures in the CHAMP magnetic field data we estimate the ocean magnetic signals of steady flow using a global 3-D EM numerical solution. The required velocity data are from the ECCO ocean circulation experiment and alternatively from the OCCAM model for higher resolution. We assume an Earth’s conductivity model with a surface thin shell of variable conductance with a realistic 1D mantle underneath. Simulations using both models predict an amplitude range of ±2 nT at Swarmaltitude (430 km). However at sea level, the higher resolution simulation predicts a higher strength of the magnetic field, as compared to the ECCO simulation. Besides the expected signatures of the global circulation patterns, we find significant seasonal variability of ocean magnetic signals in the Indian and Western Pacific Oceans. Compared to seasonal variation, interannual variations produce weaker signals.

The Swarmmission was selected as the 5th mission in ESA’s Earth Explorer Programme in 2004. The mission will provide the best ever survey of the geomagnetic field and its temporal evolution that will lead to new insights into the Earth system by improving our understanding of the Earth’s interior and its effect on Geospace, the vast region around the Earth where electrodynamic processes are influenced by the Earth’s magnetic field. Scheduled for launch in 2010, the mission will comprise a constellation of three satellites, with two spacecraft flying sideby- side at lower altitude (450 km initial altitude), thereby measuring the East-West gradient of the magnetic field, and the third one flying at higher altitude (530 km). High-precision and high-resolution measurements of the strength, direction and variation of the magnetic field, complemented by precise navigation, accelerometer and electric field measurements, will provide the necessary observations that are required to separate and model the various sources of the geomagnetic field. This results in a unique “view” inside the Earth from space to study the composition and processes of its interior. It also allows analysing the Sun’s influence within the Earth system. In addition practical applications in many different areas, such as space weather, radiation hazards, navigation and resource management, will benefit from the Swarmconcept.

A primary objective of the Swarmconstellation mission is to resolve the lithospheric magnetic field with the best achievable accuracy in order to bridge the spectral gap between satellite and airborne/marine magnetic surveys. In a series of end-to-end simulations, the possibilities of high degree field recovery were investigated. The proposed constellation consists of a higher and a lower pair of satellites. It was soon found that a constellation as such does not yet guarantee improved high degree field recovery. Of crucial importance is the orbit constellation of the lower pair of satellites. If the lower satellites follow each other, as investigated in Constellation 1, the gain of a constellation turns out to be marginal, compared to a single satellite. For Constellation 2, the lower satellites were separated in the E/W direction. In this setup, one can use the instantaneous E/W magnetic field gradient between the satellites, as well as the N/S along track gradients. Incorporating this vector gradient information results in significantly improved field resolution. Indeed, the final simulation suggests that the envisaged Swarmconstellation will enable the recovery of the lithospheric field to beyond spherical harmonic degree 130.

It is well known that models of the global geomagnetic field constructed from only measurements of the field intensity suffer from large errors arising from the Backus or perpendicular error effect. Knowledge of the location of the magnetic dip equator is in principal sufficient to eliminate this error. We investigate constraining the location of the dip equator using observations of the equatorial electrojet in intensity measurements made from the CHAMP satellite. While the models generated are inferior compared with models obtained from oriented three-component vector data, they may be of sufficient quality to allow construction of future global geomagnetic reference models in the absence of vector data.

The quiet-time geomagnetic variations at high latitudes have not been systematically studied so far. Here we present quiet-time variation results from more than two years of continuous magnetic observations in Fennoscandia and Svalbard using the IMAGE magnetometer network. The CHAMP CO2 model is found to yield an excellent secular variation correction with a simple linear trend. The effect of the magnetospheric ring current on the quiet-time field values for each component is presented with the coefficients for the expected linear correlation with the DSTindex. A general trend for these coefficients is found for the CGM latitudes from 54 to 68 degrees. In this area the diurnal variation is well in accordance with the expected seasonal Sqbehaviour. North of the Fennoscandian mainland the DSTcoefficients and the diurnal variations show an unexpected behaviour and additional current systems are presented as a likely cause. An objective, automated baseline method used in this study is also introduced as a method useful for various applications.

The radio limb sounding or occultation technique is capable of deriving accurate vertical profiles of atmospheric refractivity. This has been shown by very promising results of the first active GPS limb sounding GPS/MET experiment on Microlab 1. In this paper we report early results of ionospheric radio occultation (IRQ) measurements carried out onboard the German satellite mission CHAMP (CHAllenging Minisatellite Payload) that contributes also to essential improvements of gravity and magnetic field models of the Earth.

An unambiguous determination of the wave modes observed in plasma turbulence requires the determination of the dispersion characteristics of the wave. The method adopted for the determination of the wave dispersion relation is based upon the study of the phase difference of the waves at two closely separated spacecraft [Balikhin and Gedalin, 1993]. It is applied to observations of waves in the magnetosheath magnetic field made by AMPTE UKS and AMPTE IRM. We show that the observed waves are propagating in the sunward direction but are convected toward the magnetopause by the plasma flow. As a result, the observed waves are quasi‐standing in the flow. These waves have been previously identified as either slow or mirror modes depending the procedure adopted for their analysis. They may also be an experimental observation of the mirror and slow (MIAOW) waves identified near the magnetopause boundary in the hybrid simulations of Omidi and Winske[1995]. The observed waves possess short wavelengths (λ) such that RBi/λ ≈ 1 (where RBiis the ion Larmor radius). Thus they may only be studied analytically within the framework of the kinetic approximation. Both the nonlinear amplitudes and possibly the strong underlying inhomogeneity are responsible for the significant differences between the properties of the observed modes and those resulting from linear homogeneous kinetic theory.

Simultaneous whistler records of one station and geomagnetic pulsation (Pc3) records at three stations were compared. In a previous study correlation was found between occurrence and L value of propagation/excitation for the two phenomena. The recently investigated simultaneous records have shown that the correlation is better on longer time scales (days) than on shorter ones (minutes), but the L values of the propagation of whistlers/excitation of pulsations are correlated, i.e. if whistlers propagate in higher latitude ducts, pulsations have periods longer than in the case when whistlers propagate in lower latitude ducts.

By means of 4 years of Challenging Minisatellite Payload (CHAMP) zonal wind observations and a Thermosphere‐Ionosphere Electrodynamics General Circulation Model simulation, longitudinal and seasonal variations of thermospheric superrotation at magnetic equator are investigated first. The superrotation shows four‐ and three‐peaked longitudinal patterns in March and September equinoxes, and a two‐peaked variation during solstices. The superrotation is stronger in December than in June solstice, and stronger in March than in September equinox. The mean correlation between the zonal variation of superrotation and nighttime eastward wind is about 0.8, while it is 0.6 with daytime westward zonal wind. The interaction between the neutral wind and geomagnetic field plays a more important role in the superrotation, rather than the F‐region electron density. The lower atmospheric tides tend to suppress the superrotation, but contribute to the longitudinal patterns of the superrotation. The viscous force is also important for the longitudinal modulation of the superrotation. The low altitude atmosphere rotates together with the Earth, resulting from the friction with the surface. Owing to the high viscosity, most parts of the atmosphere at different altitudes also rotate at the same rate as the Earth. Above 200 km, however, the low‐latitude atmosphere is found to rotate 10%–20% faster than the Earth. This phenomenon is more prominent on Venus, where the atmospheric circulation speed can reach 60 times of the rotation. Although this unexpected superrotation phenomenon was discovered in the 1960s in connection with satellite orbit evaluations, its physical mechanism has not been fully elucidated to date. This study reveals for the first time that the geomagnetic field configuration and the lower atmospheric tides have important effects on the superrotation of the upper atmosphere. Both can account for the longitudinal variation in the superrotation. This theoretical study is helpful for better understanding the generation mechanism of the superrotation on Earth and other planets. Superrotation of the thermosphere exhibits large longitudinal and seasonal variationsGeomagnetic field geometry and lower atmospheric tides are vital for the longitudinal patterns of superrotationViscous force also partly contributes to the longitudinal variation in superrotation Superrotation of the thermosphere exhibits large longitudinal and seasonal variations Geomagnetic field geometry and lower atmospheric tides are vital for the longitudinal patterns of superrotation Viscous force also partly contributes to the longitudinal variation in superrotation

On 7 December 1992, a moderate substorm was observed by a variety of satellites and ground-based instruments. Ionospheric flows were monitored near dusk by the Goose Bay HF radar and near midnight by the EISCAT radar. The observed flows are compared here with magnetometer observations by the IMAGE array in Scandinavia and the two Greenland chains, the auroral distribution observed by Freja and the substorm cycle observations by the SABRE radar, the SAMNET magnetometer array and LANL geosynchronous satellites. Data from Galileo Earth-encounter II are used to estimate the IMF Bz component. The data presented show that the substorm onset electrojet at midnight was confined to closed field lines equatorward of the pre-existing convection reversal boundaries observed in the dusk and midnight regions. No evidence of substantial closure of open flux was detected following this substorm onset. Indeed the convection reversal boundary on the duskside continued to expand equatorward after onset due to the continued presence of strong southward IMF, such that growth and expansion phase features were simultaneously present. Clear indications of closure of open flux were not observed until a subsequent substorm intensification 25 min after the initial onset. After this time, the substorm auroral bulge in the nightside hours propagated well poleward of the pre-existing convection reversal boundary, and strong flow perturbations were observed by the Goose Bay radar, indicative of flows driven by reconnection in the tail.

We present the ground signatures of dynamic substorm features with particular emphasis on the event interpretation capabilities provided by the IMAGE magnetometer network. This array covers the high latitudes from the sub-auroral to the cusp/cleft region. An isolated substorm on 11 Oct. 1993 during the late evening hours exhibited many of well-known features such as the Harang discontinuity, westward travelling surge and poleward leap, but also discrete auroral forms, known as auroral streamers, appeared propagating westward along the centre of the electrojet. Besides the magnetic field measurements, there were auroral observations and plasma flow and conductivity measurements obtained by EISCAT. The data of all three sets of instruments are consistent with the notion of upward field-aligned currents associated with the moving auroral patches. A detailed analysis of the electro-dynamic parameters in the ionosphere, however, reveals that they do not agree with the expectations resulting from commonly used simplifying approximations. For example, the westward moving auroral streamers which are associated with field-aligned current filaments, are not collocated with the centres of equivalent current vortices. Furthermore, there is a clear discrepancy between the measured plasma flow direction and the obtained equivalent current direction. All this suggests that steep conductivity gradients are associated with the transient auroral forms. Also self-induction effects in the ionosphere may play a role for the orientation of the plasma flows. This study stresses the importance of multi-instrument observation for a reliable interpretation of dynamic auroral processes.

Geomagnetic storm-time variations often occur coherently at high latitude and the day-side dip equator where they affect the normal eastward Sq field. This paper presents an analysis of ground magnetic field and ionospheric electrodynamic data related to the geomagnetic storm which occured on 27 May 1993 during the International Equatorial Electrojet Year (IEEY) experiment. This storm-signature analysis on the auroral, mid-latitude and equatorial ground field and ionospheric electrodynamic data leads to the identification of a sensitive response of the equatorial electrojet (EEJ) to large-scale auroral return current: this response consists in a change of the eastward electric field during the pre-sunrise hours (0400–0600 UT) coherently to the high-, mid-, and equatorial-latitude H decrease and the disappearance of the EEJ irregularities between the time-interval 0800–0950 UT. Subsequent to the change in h’F during pre-sunrise hours, the observed foF2 increase revealed an enhancement of the equatorial ionization anomaly (EIA) caused by the high-latitude penetrating electric field. The strengthening of these irregularities attested by the Doppler frequency increase tracks the H component at the equator which undergoes a rapid increase around 0800 UT. The ?H variations observed at the equator are the sum of the following components: SR, DP, DR, DCF and DT.

For the six months from 1 October 1993 to 1 April 1994 the recordings of the IMAGE magnetometer network have been surveyed in a search for largeamplitude travelling convection vortices (TCVs). The restriction to large amplitudes (>100 nT) was chosen to ensure a proper detection of evens also during times of high activity. Readings of all stations of the northern half of the IMAGE network were employed to check the consistency of the ground signature with the notation of a dual-vortex structure moving in an azimuthal direction. Applying these stringent selection criteria we detected a total of 19 clear TCV events. The statistical properties of our selection resemble the expected characteristics of large-amplitude TCVs. New and unexpected results emerged from the superposed epoch analysis. TCVs tend to form during quiet intervals embedded in moderately active periods. The occurrence of events is not randomly distributed but rather shows a clustering around a few days. These clusters recur once or twice every 27 days. Within a storm cycle they show up five to seven days after the commencement. With regard to solar wind conditions, we see the events occurring in the middle of the IMF sector structure. Large-amplitude TCVs seem to require certain conditions to make solar wind transients ‘geoeffective’, which have the tendency to recur with the solar rotation period.

The CUTLASS Finland HF radar has been operational since February 1995. The radar frequently observes backscatter during the midnight sector from a latitude range 70–75° geographic, latitudes often associated with the polar cap. These intervals of backscatter occur during intervals of substorm activity, predominantly in periods of relatively quiet magnetospheric activity, with Kp during the interval under study being 2-and ?KP for the day being only 8-. During August 1995 the radar ran in a high time resolution mode, allowing measurements of line-of-sight convection velocities along a single beam with a temporal resolution of 14s, and measurement of a full spatial scan of line-of-sight convection velocities every four minutes. Data from such scans reveal the radar to be measuring return flow convection during the interval of substorm activity. For three intervals during the period under study, a reduction in the spatial extent of radar backscatter occurred. This is a consequence of D region HF absorption and its limited extent in the present study is probably a consequence of the high latitude of the substorm activity, with the electrojet centre lying between 67° and 71° geomagnetic latitude. The high time resolution beam of the radar additionally demonstrates that the convection is highly time dependent. Pulses of equatorward flow exceeding ~600 m s-1 are observed with a duration of ~5 min and a repetition period of ~8 min. Their spatial extent in the CUTLASS field of view was 400–500 km in longitude, and 300–400 km in latitude. Each pulse of enhanced equatorward flow was preceded by an interval of suppressed flow and enhanced ionospheric Hall conductance. The transient features are interpreted as being due to ionospheric current vortices associated with field aligned current pairs. The relationship between these observations and substorm phenomena in the magnetotail is discussed.

Based on a detailed study of Pc3 events at an array between L = 1.5 and 3 in Central Europe, the authors found quick changes between upstream waves (UW, i.e. pulsation directly driven by UW) and field line resonance (FLR, i.e. azimuthal oscillations of geomagnetic field lines). The alternation of the two types is especially characteristic (and the UW part stronger) if the interplanetary magnetic field (IMF) is highly variable. Events due to field line resonance may have a structure consisting of multiple lines with frequencies differing by about 10%, corresponding to neighbouring shells of field lines separated by about 100 km at the surface. This coincides with previous findings (about 10% at a meridional distance of 80 km). The frequency of the UW type is well correlated with the frequency of waves in the interplanetary medium. Additionally, there are signals of unidentified origin which also seem to be influenced by IMF.

Es wird über den diesjährigen Betontag berichtet, der vom 9. bis 11. April zum 57sten Mal vom Deutschen Beton‐Verein E.V., Wiesbaden, veranstaltet wurde und über 2000 Fachleute aus dem In‐ und Ausland unter dem Motto "Kreative Ingenieure fördern die Bauart" in das Berliner ICC führte.

Es wird dargelegt, unter welchen Umständen bauaufsichtlich zugelassene Flugasche aus dem Hochofenprozess als Betonzusatzstoff verwendet werden darf und welche Eigenschaften bei der Prüfzeichen‐ bzw. Zulassungsprüfung sowie bei der Eigen‐ und Fremdüberwachung nachzuweisen sind.

Changes of total (Ca) and ionized Ca-levels (Ca2) were studied during open heart surgery in 18 patients. 9 patients (group A) had only cristalloid solutions as pump priming, the other 9 patients (group B) had 500 ml of titrated whole blood in the priming solution. For assessment of hemodilution hct and total plasma protein and plasma albumin were determined. Measurements were done preoperatively, before and after systemic heparinisation, during and after extracorporeal circulation (ECC) and on the first postoperative day.Results:Anticoagulation with 375 Ukg BW heparin had no effect on ionized calcium levels.With onset of ECC (Ca) decreased by 30 in group A and by 20 in group B. (Ca2), however, decreased by 20 in group A and by 35 in group B. The percentage of ionized calcium increased by 15 in group A whereas it decreased by the same amount in group B.This difference is contributed to the calcium binding effect of citrate added to pump priming in group B. Mechanisms of the relative increase of ionized calcium during ECC in group A, however, remain to be studied.

A coordinated ground-based observational campaign using the IMAGE magnetometer network, EISCAT radars and optical instruments on Svalbard has made possible detailed studies of a travelling convection vortices (TCV) event on 6 January 1992. Combining the data from these facilities allows us to draw a very detailed picture of the features and dynamics of this TCV event. On the way from the noon to the drawn meridian, the vortices went through a remarkable development. The propagation velocity in the ionosphere increased from 2.5 to 7.4 km s-1, and the orientation of the major axes of the vortices rotated from being almost parallel to the magnetic meridian near noon to essentially perpendicular at dawn. By combining electric fields obtained by EISCAT and ionospheric currents deduced from magnetic field recordings, conductivities associated with the vortices could be estimated. Contrary to expectations we found higher conductivities below the downward field aligned current (FAC) filament than below the upward directed. Unexpected results also emerged from the optical observations. For most of the time there were no discrete aurora at 557.7 nm associated with the TCVs. Only once did a discrete form appear at the foot of the upward FAC. This aurora subsequently expanded eastward and westward leaving its centre at the same longitude while the TCV continued to travel westward. Also we try to identify the source regions of TCVs in the magnetosphere and discuss possible generation mechanisms.

We present an analysis of ground magnetic field, ionospheric flow, geosynchronous particle, and interplanetary data during a multiple-onset substorm on 12 April 1988. Our principal results concern the modulations of the ionospheric flow which occur during the impulsive electrojet activations associated with each onset. During the first hour of the disturbance these take place every \sim12.5 min and involve the formation of a new intense westward current filament in the premidnight sector, just poleward of the preexisting extended current system driven by the large-scale flow. These filaments are \sim1 h MLT wide (\sim600 km), and initially expand poleward to a width of \sim300 km before contracting equatorward and coalescing with the preexisting current, generally leaving the latter enhanced in magnitude and/or expanded in latitude. Within the impulsive electrojets the flow is found to be suppressed to values 50–100 m s-1 or less during the first few minutes, before surging equatorward at 0.5-1.0 km s-1 during the phase of rapid coalescence. The implication is that the precipitation-induced Hall conductivity within the impulsive electrojet initially rises to exceed \sim100 mho, before decaying over a few minutes. This value compares with Hall conductivities of \sim20 mho in the quasi-steady current regions, and a few mho or less in the regions poleward of the electrojets and in the preonset ionosphere. Preliminary evidence has also been found that the flow surges propagate from midnight to the morning sector where they are associated with arrested equatorward motion or poleward contractions of the current system. These observations are discussed in terms of present theoretical paradigms of the global behaviour of fields and flows which occur during substorms.

We report multi-instrument observations during an isolated substorm on 17 October 1989. The EISCAT radar operated in the SP-UK-POLI mode measuring ionospheric convection at latitudes 71°-78°. SAMNET and the EISCAT Magnetometer Cross provide information on the timing of substorm expansion phase onset and subsequent intensifications, as well as the location of the field aligned and ionospheric currents associated with the substorm current wedge. IMP-8 magnetic field data are also included. Evidence of a substorm growth phase is provided by the equatorward motion of a flow reversal boundary across the EISCAT radar field of view at 2130 MLT, following a southward turning of the interplanetary magnetic field (IMF). We infer that the polar cap expanded as a result of the addition of open magnetic flux to the tail lobes during this interval. The flow reversal boundary, which is a lower limit to the polar cap boundary, reached an invariant latitude equatorward of 71° by the time of the expansion phase onset. A westward electrojet, centred at 65.4°, occurred at the onset of the expansion phase. This electrojet subsequently moved poleward to a maximum of 68.1° at 2000 UT and also widened. During the expansion phase, there is evidence of bursts of plasma flow which are spatially localised at longitudes within the substorm current wedge and which occurred well poleward of the westward electrojet. We conclude that the substorm onset region in the ionosphere, defined by the westward electrojet, mapped to a part of the tail radially earthward of the boundary between open and closed magnetic flux, the “distant” neutral line. Thus the substorm was not initiated at the distant neutral line, although there is evidence that it remained active during the expansion phase. It is not obvious whether the electrojet mapped to a near-Earth neutral line, but at its most poleward, the expanded electrojet does not reach the estimated latitude of the polar cap boundary.

The geomagnetic response to the passage of a coronal mass ejection (CME) is studied. The passage of the CME resulted in a storm sudden commencement (SSC) at 2243 UT on March 20 1990 with disturbed magnetic activity during the following 24 h. The auroral, sub-auroral and equatorial magnetic response to the southward turning at 1314 (±5) UT on March 21 and the equatorial response to the southward turning associated with the SSC on 20 March are discussed in terms of existing models. It is found that the auroral and sub-auroral response to the southward turning associated with the SSC is a factor 2 or more quicker than normal due to the shock in the solar wind dynamic pressure. The low-latitude response time to the south-ward turning, characterised by Dst and the magneto-pause current corrected Dst*, is una.ected by the shock. Dst and Dst*, characteristic of the equatorial magnetic field, responded to the 1314 (±5) UT southward turning prior to the first observed substorm expansion phase onset, suggesting that a dayside loading process was responsible for the initial enhancement in the ring current rather than nightside particle injection. The response time of the auroral and sub-auroral magnetic field to the southward turning at 1314 (±5) UT on March 21 is measured at a variety of longitudes and latitudes. The azimuthal propagation velocity of the response to the southward turning varied considerably with latitude, ranging from #x0223C;8 km s-1 at 67°N to ~4 kms-1 at 55°N. The southward velocity of the equatorward boundary of the northern polar convection pattern has been measured. This velocity was ~1.2 km s-1 at 1600 MLT, although there was evidence that this may vary at different local times.

Convection electric fields, Ec= −Vp×B, measured during a magnetopause/boundary layer encounter at low latitude by the AMPTE/IRM spacecraft, are shown to yield an accurate determination of the magnetopause normal vector, N, even though the magnetic shear across the magnetopause was small. The average plasma velocity along N is used to deduce a boundary layer thickness of about 1.3 RE. Analysis of Ecin the magnetopause itself reveals the existence of a deHoffmann‐Teller frame in which the flow is nearly field aligned and approximately Alfvénic, indicating that the magnetopause was a rotational discontinuity; this is interpreted as a signature that magnetic‐field reconnection was occurring somewhere on the magnetopause.

The Cluster mission provides a new opportunity to study plasma processes and structures in the near-Earth plasma environment. Four-point measurements of the magnetic field will enable the analysis of the three dimensional structure and dynamics of a range of phenomena which shape the macroscopic properties of the magnetosphere. Difference measurements of the magnetic field data will be combined to derive a range of parameters, such as the current density vector, wave vectors, and discontinuity normals and curvatures, using classical time series analysis techniques iteratively with physical models and simulation of the phenomena encountered along the Cluster orbit. The control and understanding of error sources which affect the four-point measurements are integral parts of the analysis techniques to be used. The flight instrumentation consists of two, tri-axial fluxgate magnetometers and an on-board data-processing unit on each spacecraft, built using a highly fault-tolerant architecture. High vector sample rates (up to 67 vectors s-1) at high resolution (up to 8 pT) are combined with on-board event detection software and a burst memory to capture the signature of a range of dynamic phenomena. Data-processing plans are designed to ensure rapid dissemination of magnetic-field data to underpin the collaborative analysis of magnetospheric phenomena encountered by Cluster.

Magnetometers aboard the IRM and UKS spacecraft monitored the magnetic field during the AMPTE artificial comet experiment of 27 December 1984. Rapid photoionization of the released barium vapour resulted in the formation of a magnetic cavity, shielded from the ambient magnetic field. The presence of this highly conductive obstacle caused draping and compression of the solar wind magnetic field.

A description of a new magnetometer network in northern Scandinavia is presented. The network, the ‘EISCAT-Magnetometer Cross’, is a cooperative project between Scandinavian and German research groups. It consists of seven continuously recording digital magnetometer stations. A special feature of the instruments is their almost maintainance free operation. The hardware has been developed at the Technical University of Braunschweig, F.R.G., and represents the state-of-the-art in digital magnetometer stations.

Using data on the occurrence frequency of geomagnetic pulsations of different periods from three observatories in Central Europe, conclusions are drawn about the occurrence of field line resonances and pulsations directly driven by upstream waves at L-values below 3. It was found that both types occur during the interval studied (first 6 months of the year 1991), but both the occurrence frequency of the two types and the characteristic period of the field line resonance change significantly as compared to other intervals. During Northern winter, pulsation activity is severely damped in solar maximum years, including the year 1991. The decrease in the activity of the pulsations is more significant at shorter periods.

Observations are presented of data taken during a 3-h interval in which five clear substorm onsets/intensifications took place. During this interval ground-based data from the EISCAT incoherent scatter radar, a digital CCD all sky camera, and an extensive array of magnetometers were recorded. In addition data from the CRRES and DMSP spacecraft, whose footprints passed over Scandinavia very close to most of the ground-based instrumentation, are available. The locations and movements of the substorm current system in latitude and longitude, determined from ground and spacecraft magnetic field data, have been correlated with the locations and propagation of increased particle precipitation in the E-region at EISCAT, increased particle fluxes measured by CRRES and DMSP, with auroral luminosity and with ionospheric convection velocities. The onsets and propagation of the injection of magnetospheric particle populations and auroral luminosity have been compared. CRRES was within or very close to the substorm expansion phase onset sector during the interval. The onset region was observed at low latitudes on the ground, and has been confirmed to map back to within L=7 in the magnetotail. The active region was then observed to propagate tailward and poleward. Delays between the magnetic signature of the substorm field aligned currents and field dipolarisation have been measured. The observations support a near-Earth plasma instability mechanism for substorm expansion phase onset.

Ground‐based observations of auroral, geomagnetic, and radar signatures of solar wind‐magnetosphere coupling modes are presented. Two different categories of ionospheric signatures are studied: (1) enhanced geomagnetic deflections and associated equatorward displacements of the cusp/cleft aurora and (2) a sequence of poleward moving auroral and geomagnetic events. It is suggested that signature 1 is mainly caused by directional discontinuities in the interplanetary magnetic field changing the solar wind‐magnetosphere coupling geometry and that signature 2 is caused by a recurring modulation of the reconnection rate at the dayside magnetopause (flux transfer events (FTEs)), during the period of strong coupling. The observed auroral and geomagnetic signatures are placed in the context of plasma convection, as derived from magnetometers in Svalbard, Greenland, and Canada, and the European incoherent scatter (EISGAT) radar. A suggestion for an ionospheric current system explaining the sequence of poleward propagating events, i.e., the FTE signatures, is presented.

The development of groundwater models solving actual engineering problems is of great interest as well with regard to physical as with regard to economical aspects. These models enable a more precise treatment of problems during the stage of planning. Furthermore, these models assure a permanent control of finished steps. Generally, the flow through porous media is a three-dimensional process depending on various parameters. Normally, this process is so complicated that it is not possible to describe the situation in nature in a general form. Therefore, it is necessary to develop some simplified physical models of groundwater flow which are adapted to relevant individual circumstances. These refer for example to steady or unsteady flow, to flow with or without a free surface, to flow in an isotropic or anisotropic aquifer, to one-, two- or three-dimensional flow. The solution of these different physical models can be obtained by use of analytical, analog or digital methods, which consider the typical physical conditions. Such a concept of a physical model and a corresponding solution method is to be defined as a socalled analytical, analog or digital flow model through porous media. As the organization of flow models through porous media causes generally high costs, which c1epend mainly on the choice of the solution method, it is of great interest, which of the different solution methods is suitable for a given problem. It was possible to prove by a cost-effectiveness-analysis, that digital solution methods generally are considerably more effective than analytical and analogous methods. As digital solution methods, one can use either the method of finite elements or the method of finite differences. Both methods produce discrete solutions of given problems. The comparison of both methods is to be done by significant criteria. These are: 1. the required core storage; 2. the required computing time; 3. the flexibility of the methods approximating the problems. As the core storage and the computing time c1irectly depend on the organization technique and the algorithm solving linear equation systems, special organization techniques are to be discussed. The flexibility is to be seen in clependence on physical problems. The comparison of both methods (methods of finite elements and finite differences, respectively) shows, that the method of finite differences is much more better with regard to organization and programming aspects, especially however, with regard to economical aspects (Jess required core storage, less computing time). In general, flow problems through porous media should be solved by the method of finite differences. For all problems, however, which involve an automatic search of free surfaces, the method of finite elements appears to be more suitable, because only its organization can realize these problems.

A global distribution of the thermospheric total mass density at 400 km altitude is derived from the high‐accuracy accelerometer on board the CHAMP satellite with good temporal and spatial coverage. It shows two interesting features. One is the anomalous distribution at low latitudes. Instead of maximizing at the dayside equator, the thermospheric density shows maxima at about 20°–25° geomagnetic latitude on both sides of the equator between 10 and 20 magnetic local time. This latitudinal distribution resembles fairly well the equatorial ionization anomaly, thus indicating strong magnetic control of the thermospheric mass density via ionosphere‐thermosphere coupling. The thermospheric density shows a secondary maximum at the nightside equator shortly before midnight, in reminiscence of the well‐known thermospheric midnight temperature maximum. Another feature to notice is that the thermospheric density is highly structured at high latitudes, with localized density enhancements possibly related to Joule/particle heating. This structure is, however, different from the cellular structure recognized by the National Center for Atmospheric Research thermosphere general circulation model at altitudes of 120–300 km. This indicates that the exact cellular structure may not necessarily extend to 400 km. A comparison between observations and the Mass Spectrometer Incoherent Scatter 1990 (MSIS90) model predictions shows that although the model describes the general structure of the observed density reasonably well, it misses the double peaks at low latitudes completely. This causes an underestimation of the total mass density by 15–20% in the crest region. At high latitudes an underestimation of 20–30% occurs in the midnight sector and the cusp region. Outside these localized areas the agreement between observations and predictions is quite good, with only ∼5% difference on average under quiet geomagnetic conditions.