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[1] We use a three-dimensional global magnetohydrodynamic (MHD) simulation code to examine the energy flow from the solar wind to the magnetosphere. We simulate a major magnetic storm, which occurred on 6-7 April 2000. During this disturbed period the energy input to the magnetosphere was highly enhanced. For the energy transfer calculation a method for identifying the magnetopause surface from the simulation is developed. We calculate the total energy flux component normal to the magnetopause surface, thus giving the energy flux transferred from the solar wind to the magnetosphere. With this method we identify the locations on the magnetopause surface where significant energy transfer takes place during the storm evolution. During the main phase the energy is transferred from the plane parallel and antiparallel to the interplanetary magnetic field (IMF) clock angle Sunward of X GSE > À10 R E . During the recovery phase most of the energy is transferred in the low-latitude equatorial sectors Sunward of the dawn-dusk terminator. We discuss the possible explanations to the observed energy transfer locations. We also compare the time evolution of the total transferred energy to the time evolution of the empirical parameter calculated from the solar wind parameters. During the main phase the total transferred energy in the simulation is well correlated with , although it is about four times larger. During the recovery phase the total transferred energy and are not well correlated, and their ratio is much larger than during the main phase. Finally, we discuss limitations of the developed method, which is based on calculating fluxes through surfaces using surface integrals.

Abstract. We investigate with the help of a magnetohydrodynamic (MHD) model how the large-scale topology of the magnetosphere develops for a constant interplanetary magnetic field (IMF) with different IMF clock angles and for an IMF B y sign change during northward IMF. A detailed examination of the topological changes in the tail and the ionosphere for different IMF conditions shows a good agreement with observational results.The MHD simulations for different constant IMF clock angle cases show the expected field-line bending and tail twisting for nonzero IMF B y . The tail becomes longer and at its tailward end stronger twisted for IMF B z >|B y | than for IMF B z <|B y |. The field lines originating in the high-latitude flank of the far-tail plasma sheet map into the near-Earth tail lobes and to a strongly poleward displaced polar cap boundary. A comparison with observations suggests that an ovalaligned arc may occur on the high-latitude part of the polar cap boundary.An IMF B y sign change causes large deformations of the tail. After the IMF B y flip the near-Earth and far-tail plasma sheet regions are oppositely twisted which causes in the nearEarth tail a bifurcation of the closed field line region that moves from one flank to the other. The bifurcated part of the closed field line region maps to a bridge of closed field lines moving over the entire polar cap. This moving bridge may be interpreted as the mapped region of a moving transpolar arc. Based on earlier observations, such a type of polar arcs is expected to occur after an IMF B y sign change.

Abstract.One possibility for propellantless propulsion in space is to use the momentum flux of the solar wind. A way to set up a solar wind sail is to have a set of thin long wires which are kept at high positive potential by an onboard electron gun so that the wires repel and deflect incident solar wind protons. The efficiency of this so-called electric sail depends on how large force a given solar wind exerts on a wire segment and how large electron current the wire segment draws from the solar wind plasma when kept at a given potential. We use 1-D and 2-D electrostatic plasma simulations to calculate the force and present a semitheoretical formula which captures the simulation results. We find that under average solar wind conditions at 1 AU the force per unit length is (5±1)×10 −8 N/m for 15 kV potential and that the electron current is accurately given by the well-known orbital motion limited (OML) theory cylindrical Langmuir probe formula. Although the force may appear small, an analysis shows that because of the very low weight of a thin wire per unit length, quite high final speeds (over 50 km/s) could be achieved by an electric sailing spacecraft using today's flight-proved components. It is possible that artificial electron heating of the plasma in the interaction region could increase the propulsive effect even further.Keywords. General or miscellaneous (Instruments useful in three or more fields; New fields (not classifiable under other headings); Techniques applicable in three or more fields)