In Figure 4b, the dotted line represents the model field contributions from just the solar wind dynamic pressure variations. The contributions are primarily in the x direction and result from an increase in magnetopause currents as well as tail and field aligned currents associated with the changes in dynamic pressure.
One of the most interesting features is the narrow positive peak in the contribution to dBx at 1100 UT on Jan 10. In Figure 3 this peak is seen very strongly in the measured dBx field and to a lesser extent in the model dBx field. Comparing this time interval to the solar wind parameters in Figure 1 it is apparent that this feature is indeed due to a small sharp impulse in dynamic pressure at approximately the same time. The response of the T96_01 model to this pressure pulse greatly underestimates the actual response. In fact during all periods of strong dynamic pressure the model has difficulty reproducing the measured fields.
There are other significant enhancements in dynamic pressure, for example between 0200 and 0400 UT on Jan 11, which do not produce nearly as great an effect as the 1100 UT Jan 10 pressure pulse. These relatively weaker responses to dynamic pressure may be due to the fact that the IMF is not strongly southward as it is on Jan 10 implying that the solar wind dynamic pressure may have a much larger effect during periods of southward IMF. In support of this is the simultaneous peak in the model field contributions from both Pdyn and IMF on Jan 10 near 1100 UT as seen in Figure 4b.
© 1998 AGU