Abstract. In the recent past, three-dimensional global MHD codes have successfully demonstrated that they are invaluable tools for simulating global magnetopheric phenomena. In this paper, using the Lyon-Fedder-Mobarry code, we present results on the spatial structure of the steady state of Earth's magnetosphere for northward interplanetary magnetic field (IMF). We have shown that the steady state tail length of the Earth's magnetosphere for northward IMF is short and that the three-dimensional structure of the tail lobe is on concave shape. This is in contradiction to the results presented by Fedder and Lyon [1995]. Explanation for this discrepany is given in this paper. By varying the simple time-independent solar wind velocity and interplanetary magnetic field, we present the parametric (power law) dependence of the geometrical aspects of the tail lobe on solar wind condition. In general, with higher solar wind velocity the radius of the tail lobe cross section is smaller and tail length is longer. With higher northward IMF the whole tail lobe is smaller. These numerical studies have guided us in building analytical models based on global conservation constraints and force balance. We conclude that the lobe size is mainly determined by the solar wind velocity and the reconnection process in the cusp region which is affected by the magnitude of the IMF. We also show that the ionospheric effects are not significant in determining the lobe size. The evolution history of the tail length for magnetotail to reach steady state is also presented in this paper. Emphasis is placed on the fact that the steady state is a dynamical steady state.

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