Magnetopause erosion and unsteady magnetic field line reconnection

Research project P 13804 Magnetopause erosion and reconnection Helfried K. BIERNAT 28.06.1999 Planetary magnetic fields, like that of the Earth, are influenced considerably by the solar wind. The solar wind plasma deforms the planetary magnetic field and confines it to a finite region which envelops Earth and is commonly called magnetosphere. For typical solar wind parameters the subsolar standoff distance of the boundary surface, the magnetopause, is approximately 10 Earth radii. As investigated in the early 1960s this standoff distance can be found from pressure balance of the planetary magnetic field pressure and the dynamic pressure of the solar wind. When parameters defining the pressure balance change, the position of the magnetopause will also vary. Under special circumstances, however, the magnetopause moves inwards even when the dynamic solar wind pressure remains unchanged. This phenomenon is called erosion and has already been identified in the 1970s. Quite generally, erosion happens during intervals when the interplanetary magnetic field (MV) has a persistent north-south component. Nevertheless, the physics of dayside magnetosphere erosion is still only partially understood. One important goal of the project will be to analyse the various existing approaches describing the erosion process and to put them into a global perspective. To understand better the effects of magnetosphere erosion, it is necessary - in our view - to take into account a variety of interrelated phenomena (i.e., the appearance of the magnetic barrier; unsteady (bursty) reconnection of the IMF and the magnetospheric magnetic field; consequences of reconnection). After a careful investigation of all these effects it is possible to analyze pressure balance and to investigate the erosion phenomenon in detail. The aim of this project is to present a new physical model for the erosion process of the magnetopause combined with a clear formulation of the mathematics involved, and model predictions. The study will be complemented by a thorough data analysis. The main focus will lie hereby on the investigation of new multi-point observations. Project results will then be published in most reputed international journals, such as the American Journal of Geophysical Research and others. The work is imbedded in a collaboration with the United States (Prof. C. I Farrugia from the University of New Hampshire; he has enormous knowledge of and expertise in data analysis and interpretation), Russia (Prof. V. S. Semenov from the University of St. Petersburg; he is an expert in the theoretical description of the problem), and others. The proposed working group has experience in the calculation of the plasma and magnetic field behavior in the magnetic barrier, the examination of reconnection at the magnetopause, and the comparison of model predictions with data. Therefore we are able to fulfill the following points: a) Elaboration of a time dependent model for the magnetic barrier and investigation of the time period for re-establishing the magnetic field intensity after a reconnection pulse. b) Extension of the unsteady reconnection model for the case of a magnetic barrier and investigation of pressure balance in the course of reconnection pulses. c) Study the consequences of reconnection, such as the Birkeland current loop and its influence on pressure balance. d) Work on data of satellites like Geotail, IMP 8, Wind, Interball, ISEE1-2, and others. e) Comparison of model predictions with satellite data showing 1) cases where a sustained southward IMF was not accompanied by significant pressure changes and 2) extreme conditions like interplanetary magnetic clouds.