The MFE residual fields during three successive apogee passes of the POLAR satellite exhibit distinctive features superimposed upon similar general trends. The similar trends which, in SM coordinates, include positive dBx and dB, negative dBz, and a reversal of dBy, are a result of quiet time magnetopause, tail and ring currents. The distinctive features are attributed to the variable solar wind and Dst parameters. The ring current has a large effect on both the inner and outer magnetosphere during the magnetic cloud passage being responsible for most of the observed By, Bz and total B residuals along all three apogee passes. The effect of the ring current is greatest in the near equatorial regions during the Jan 10 interval when the IMF is southward. There is also evidence for a dawn-dusk asymmetry in the ring current strength during the main phase of the Jan 10 magnetic storm. The solar wind dynamic pressure and IMF variability are responsible for the shorter time scale variations with the dynamic pressure having greater effect during periods of southward IMF. There are two instances where field aligned current effects are seen. Both of these instances are during the southward IMF portion of the magnetic cloud and are seen at the lower altitude portion of the apogee trajectories at radial distances of ~4-6 RE.
The response of the magnetosphere to the passage of the magnetic cloud is modeled very effectively by the T96_01 model. The model has proved to be a very useful tool in determining the solar wind control of the magnetic fields at high altitudes above the north pole.
© 1998 AGU