Réponses transitoires de la convection ionosphérique dans le secteur jour aux stimuli du milieu interplanétaire

PARIS-BIUSJ-Thèses (751052125) / SudocCentre Technique Livre Ens. Sup. (774682301) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Current layers: Influence of the finite size and non-uniform current distribution.

One of the key parameters of the auroral regions is the currents which flow parallel to the magnetic field and transfer the energy and momentum between the ionosphere and the external regions of the magnetosphere. Satellite magnetic field measurements provide information about such currents. The commonly adopted technique to deduce the current characteristics from the magnetic perturbations is based on the approximation of current sheet of three dimensions, two of them, i.e. along the magnetic field and in a perpendicular direction, are infinite. This approach is valid when the magnetic perturbations are observed far from the current edges, which is not always the case. In this paper, we compare the infinite sheet approximation with the solution for the current layer of finite transverse sizes and discuss the influence of the current edges on the deduced parameters. In addition, the current distribution inside the layer is rarely uniform, but comprises filamentary structures with typical sizes that correspond to the characteristic scales of the processes which originate them. Both, the filamentary currents and the current sheet edges, create a component of the magnetic perturbation normal to the current sheet, which is absent in the model of the infinite uniform current layer. The discussion is illustrated with simultaneous observations of a current double-layer made at the altitude of 860 km by the magnetometers on board the Ørsted satellite and at ∼300 km by the coherent SuperDARN radars

Extension of SuperDARN at Dome C.

Dome C Astronomy and Astrophysics Meeting, M. Giard, F. Casoli and F. Paletou (eds)International audienceThe SuperDARN (Super Dual Auroral Radar Network) experiment is a multinational effort to develop chains of coherent HF radars world wide in order to obtain instantaneous large scale coverage of the magnetospheric plasma convection at high spatial and temporal resolution. We will review the scientific context of the experiment. The role of SuperDARN in our understanding of Sun-Earth relations will be emphasized through its numerous scientific objectives. The principle of the experiment will be described and specific capabilities and achievements presented, as well as its implication in the Space Weather program. Finally, the implementation of SuperDARN radars at Dome C is presented together with the prospective global extension of the network in both hemispheres

Benard-Marangoni convective instability in presence of a magnetic field

info:eu-repo/semantics/publishe

Structure of field-aligned currents in the polar cusp: conjugated observations by Cluster, Double Star-2 and SuperDARN

Dayside field-aligned currents flowing along highly conductive field lines transmit magnetic stress caused by magnetopause reconnection, to the magnetosphere and the conjugated ionosphere. On 20 February 2005, Cluster at high altitude and Double Star-2 (TC-2) at mid altitude are situated in the vicinity of the northern cusp / mantle, with Cluster moving sunward and TC-2 anti-sunward. Their magnetic footprints come very close together at about 15:45 UT, just over the common field-of-view of SuperDARN radars. Based on this conjunction, we compare the transverse structure (form/elongation) of field-aligned current tubes at different altitudes, their intensity, their temporal dynamics, the associated particle carriers and their closure in the ionosphere. Cluster field-aligned currents are determined from the multi-satellite curlometer technique and compared to the currents determined from the single-satellite method based on the infinite current sheet hypothesis. This last method is also used to calculate currents from TC-2 magnetic data. The good comparison between drift velocity of injections calculated from the four-spacecraft timing technique and convection field measured by SuperDARN, allows to take into account the drift of the injection structures in the current calculation. Finally, fieldaligned currents deduced from magnetic measurements are also compared with electron and ion fluxes measured onboard Cluster and TC-2

What can we learn from HF signal scattered from a discrete arc?

International audienceWe present observations of a discrete southward propagating arc which appeared in the mid-night sector at latitudes equatorward of main substorm activity. The arc observations were made simultaneously by the ALFA (Auroral Light Fine Analysis) optical camera, the SuperDARN-CUTLASS HF radar and the Demeter satellite during a coordinated multi-instrumental campaign conducted at the KEOPS/ESRANGE site in December 2006. The SuperDARN HF signal which is often lost in the regions of strong electron precipitation yields in our case clear backscatter from an isolated arc of weak intensity. Consequently we are able to study arc dynamics, the formation of meso-scale irregularities of the electron density along the arc, compare the arc motion with the convection of surrounding plasma and discuss the contribution of ionospheric ions in the arc erosion and its propagation