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Introduction

The impact of a magnetic cloud with the Earth such as the January 1997 event provides an ideal opportunity for the study of the coupling between solar wind and magnetosphere. Of particular interest in this paper is the effect of the varying solar wind conditions on the high latitude, high altitude magnetosphere, as determined by the magnetic fields experiment (MFE) on POLAR [Russell et al., 1995]. By comparing the observed fields during successive apogee passes, each characterized by significantly different solar wind conditions, we can gain insight into how the high altitude magnetosphere responds to those different conditions. The T96_01 model is used as a tool to determine which solar wind and Dst parameters are most likely responsible for the observed magnetic field variations. The T96_01 model is controlled by the solar wind dynamic pressure (Pdyn), interplanetary magnetic fields (IMF By and Bz), and the Dst index [Tsyganenko, 1995, 1996; Tsyganenko and Stern, 1996].

The solar wind and Dst parameters during the January 1997 magnetic cloud event are presented in Figure 1. The three intervals to be investigated are highlighted and include a wide range of solar wind conditions which should produce markedly different magnetospheric responses. The POLAR Magnetic Fields Experiment monitors these responses along the satellite's trajectory as it passes through the high altitude near-terminator magnetosphere. An investigation of the POLAR MFE fields at perigee during the Jan 1997 event reported in a companion paper [Le et al., 1998] illustrates the different sensitivity at low altitudes to the passage of magnetic clouds.



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Next: Observations and Model Results Up: POLAR magnetic field observations Previous: POLAR magnetic field observations

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