Results 1 - 10 of 5581
Results 1 - 10 of 5581. Search took: 0.022 seconds
|Sort by: date | relevance|
[en] The investigators published a very large number of space science research papers, and in almost all cases these papers involved correlative multi-spacecraft studies. A tabulation of these research papers is provided. Quarterly progress reports for the second contractual period are included
[en] Whistlers observed on the ground, in several stations at different latitudes and longitudes, are used to compare various methods of determining whistler parameters in the absence of causative spheric and nose frequency. The Corcuff (1977) method (or CH method) is applied to a large number of whistlers recorded at Kerguelen during a period of several hours. The results show that this method is sufficiently accurate to detect slow variations of the characteristic whistler parameters, and thence the motions of the cold plasma in the magnetosphere
[fr]Des sifflements observes au sol, en des stations de latitudes et de longitudes tres diverses, sont utilises pour comparer differentes methodes d'analyse ne necessitant la connaissance ni de la frequence de 'nose', ni celle de l'atmospherique origine. La methode proposee par Corcuff P. (1977), ou methode CH, est appliquee a un nombre important de sifflements enregistres a Kerguelen au cours de plusieurs heures consecutives. L'etude des resultats montre que cette methode est suffisamment precise pour que des variations lentes des parametres fsub(n), tsub(n) des sifflements soient mises en evidence, variations qu'il est important de connaitre pour determiner les mouvements du plasma froid dans la magnetosphere
[en] Using the relation proposed by Ho (1974) and a property of the function Q(f)=(t√f)-1 relative to a whistler (Corcuff P. and Corcuff Y., 1973) the method described in this paper gives, with a good approximation, the nose frequency fsub(n) and the minimum group delay tsub(n) when fsub(n) and the causative spheric are unknown. Different relations used in this method enable us to give an interpretation of the empirical relation found by Dowden and Allcock (1971), and to justify the corrections proposed by some authors using the linear approximation for the function Q(f). Theoretical whistlers are used to compare the different methods and to determine the uncertainties due respectively to the measurements, to the extrapolation factor, to the ionospheric propagation and to the electron concentration models
[fr]Utilisant la relation de Ho (1974) et une propriete caracteristique de la fonction Q(f)=(t√f)-1 d'un sifflement electronique (Corcuff P. et Corcuff Y., 1973), la methode decrite permet de determiner avec une bonne precision la frequence de 'nose' fsub(n) et le temps de propagation tsub(n) correspondant, fsub(n) n'etant pas directement observable et l'atmospherique initial n'etant pas identifiable sur le spectrogramme du sifflement. Les relations utilisees permettent de donner une interpretation de la relation empirique trouvee par Dowden et Allcock (1971) et de justifier les corrections proposees par certains auteurs utilisant l'approximation lineaire de la fonction Q(f). Des sifflements theoriques sont utilises pour comparer differentes methodes d'analyse et pour determiner les incertitudes dues respectivement aux mesures, au facteur d'extrapolation, a la propagation ionospherique et aux modeles d'ionisation choisis
[en] In addition to the harmonic analysis of quasi-logarithmic indices Km, Kn, and Ks (part I of the present paper) a corresponding analysis of a 14-year series of linear indices am, an, and as has been carried out for the purpose of studying the effect of a varying activity level. The results for both diurnal and semi-diurnal UT waves are again in full accordance with the theoretical concept of magnetospheric modulation of geomagnetic activity. By subdividing the data into days of high and low activity, it is shown that the daily amplitudes of the diurnal wave, as well as the annual modulation amplitudes, clearly depend on the activity level in a multiplicative form. At the same time the specific selection of the data causes a curvature effect of opposite sign for the two levels considered which can be eliminated by means of a further harmonic analysis with an altered initial time of the fundamental interval
[en] Complete text of publication follows. The complex system of the Earth's magnetosphere corresponds to an open spatially extended nonequilibrium (input - output) dynamical system. The non-extensive Tsallis entropy has been recently introduced (Balasis et al., 2008) as an appropriate information measure to investigate dynamical complexity in the magnetosphere. The method has been employed for analyzing Dst time series and gave promising results, detecting the complexity dissimilarity among different physiological and pathological magnetospheric states (i.e., pre-storm activity and intense magnetic storms, respectively). This paper explores the applicability and effectiveness of a variety of computable entropy measures (e.g. Block entropy, Kolmogorov entropy, T complexity and Approximate entropy) to the investigation of dynamical complexity in the magnetosphere. We show that as the magnetic storm approaches there is clear evidence of significant lower complexity in the magnetosphere. The observed higher degree of organization of the system agrees with that inferred previously (Balasis et al., 2006), from an independent linear fractal spectral analysis based on wavelet transforms. This convergence between nonlinear and linear analyses provides a more reliable detection of the transition from the quiet-time to the storm-time magnetosphere, thus showing evidence that the occurrence of an intense magnetic storm is imminent. More precisely, we claim that our results suggest an important principle: significant complexity decrease and accession of persistency in Dst time series can be confirmed as the magnetic storm approaches, which can be used as diagnostic tools for the magnetospheric injury (global instability). Overall, Approximate entropy and Tsallis entropy yield superior results for detecting dynamical complexity changes in the magnetosphere in comparison to the other entropy measures presented herein. Ultimately, the analysis tools developed in the course of this study for the treatment of Dst index can provide convenience for space weather applications.
[en] Complete text of publication follows. Differences in the external part of the vertical geomagnetic component point to the existence of local inhomogeneities in the magnetosphere or the ionosphere. The correlations between the new magnetic index η and the ionospheric characteristics - foE (E layer critical frequency) monthly median deviations - are analysed. The analysis was based on one-minute data recorded at each of 20 European Magnetic Observatories working in the INTERMAGNET network and from 18 ionosondes for 2004. The high peaks (2-2.7) of the new magnetic index correlate in time with large (+1.6 MHz and -1.1 MHz) punctual median deviations of foE. Such punctual deviations can suggest local inhomogeneities (vertical drifts) in the ionosphere. The correlation in space is not trivial. The strong peak of ? is situated on the map between the positive and negative deviations of foE. Additional observation is connected with correlation in time of the high ? value with the negative median deviations of h'F2 (in some cases up to -90 km). The increase of the electromagnetic activity can cause lightnings in troposphere. Ionospheric data are sparse in time and in space in opposite to the magnetic data. The map of the magnetic indices can suggest the behaviour of ionospheric characteristics in the areas where we have no data.