Student project work in Space Plasma Physics

Statistics of the energy transfer between the solar wind and the magnetosphere

Student project (Examensarbete, 20 p)
Completed January 2007

Student: Johan Falkenström
Supervisor: Lisa Rosenqvist
Swedish Institute of Space Physics, Uppsala
Department of Astronomy and Space Physics, Uppsala University

Background. Our planet is strongly influenced by the Sun. Intense and time varying magnetic fields embedded in the outflowing solar wind can couple with the terrestrial magnetic field leading to energy transfer between the solar wind and our magnetosphere. The variability of this energy coupling is reflected in rapid variations in the direction and intensity of the Earth magnetic field in the form of geomagnetic storms and substorms. One of the main tasks in space physics research is to increase the knowledge of the spatial and temporal variation of this coupling and its influence on solar wind parameters and the interplanetary magnetic field. Previously the energy input to the magnetosphere has been estimated with various coupling functions derived from solar wind measurements. However, with the multi-spacecraft mission Cluster there are improved techniques to determine the local energy transfer directly by observational means at the magnetopause.

Project. We use the multi-spacecraft mission Cluster to make observational estimates of the local energy transfer across the magnetopause. 15 magnetopause crossings at different spatial locations and during varying interplanetary conditions have been investigated. We attempt to determine the spatial dependence of the local energy transfer and the influence of varying interplanetary magnetic field conditions on the estimated energy transfer magnitude.

Results. The local energy transfer is found to be positive, i.e. transferred from the magnetic field to the particles, as expected when Cluster is close to a reconnection region and detects high-speed plasma jets. When Cluster is located on the flanks of the magnetopause the energy input is strongly dependent on the location and on interplanetary conditions. For southward IMF the energy transfer is negative corresponding to the inflow of energy from the solar wind to the magnetosphere and varies with the magnitude of the southward component and the spatial location of the observation. For northward IMF there is positive energy flow close to reconnection zones otherwise no or little energy flow across the magnetopause flanks. The observations are in good agreement with the current understanding on where and how the energy is transferred across the magnetopause. However, a larger statistical set of magnetopause crossings is needed in order to draw quantitative conclusions on the interplanetary as well as spatial dependence on the magnitude of the local energy transfer.

The Earth's magnetopause, with the localtion of one of the Cluster satellites and the closest point on the magnetopause marked. The normal to the magnetopause through the satellite is shown as a blue line. The magnetopause is plotted using the Shue et al model (see project report for details).

http://www.space.irfu.se/exjobb/2006_johan_falkenstrom/index.html
last modified onWednesday, 17-Jan-2007 09:45:12 CET