Averaged behavior of the solar wind parameters in the vicinity of auroral breakups

A.A. Arykov, Yu.P. Maltsev, and I.V. Golovchanskaya
(Polar Geophysical Institute, Apatity)

Statistical study of 311 breakups detected by the Polar spacecraft since January till June, 1997, revealed no sufficiently sharp changes in the averaged behavior of the IMF Bz component, IMF modulus, solar wind velocity and density, as well as in the deviation of these parameters. The threshold effect in the solar wind dynamic pressure is not detected either. Thus, the transition from the substorm growth stage to the explosive stage seems to be caused rather by some interior magnetospheric processes. However a possibility remains for breakups to be triggered by the reverse of the time derivative of the averaged IMF Bz component observed near the breakups.