The POLAR spacecraft is in a high inclination orbit with an apogee of 9 Re over the north pole, a perigee of 1.8 Re, and a period of 17.5 hours. As an example the orbital trajectory for the Jan 10 interval is shown in Figure 2. Similarly, the trajectories corresponding to the other two intervals also lie close to the dusk-dawn plane above the north pole, beginning at dusk and ending at dawn. The observed MFE fields for all three intervals are shown in Figure 3 together with the T96_01 model fields. All observed fields are the residual fields from the International Geomagnetic Reference Field at epoch of date (IGRF 95 model) while the T96_01 fields include only the external model fields determined using the observed solar wind and Dst parameters as input. The model is correctly predicting the observations when the dotted line overlays the solid line.
As expected there are some significant differences between the three time periods as a result of the different solar wind conditions. However, there are also some general trends which are consistent from one apogee pass to the next. For example, the Bx and total B field residuals are consistently positive, the By residual reverses across the polar cap, and the Bz residual is consistently negative. For the most part there is good agreement with the T96_01 model on each of these days. The greatest disagreements with the model occur during periods of the most extreme solar wind conditions. In the following section we discuss which current systems and solar wind inputs contribute to these magnetic field residuals.
© 1998 AGU