The influence of IMF-Bz and/or AE on the polar cusp: An overview of observations from the AUREOL-3 satellite

Experimental evidence for direct or indirect effects of the polarity and amplitude of the IMF- Bz component and the activity index AE on particle precipitation in the low-altitude cusp have been searched for, using the particle data from the AUREOL-3 satellite. The observations show that the precipitation of H ⁺ and He ⁺⁺ ions often display energy-latitude dispersions over 1 to 2° in latitude which reflect the signature of the direct injection of plasma from the magnetosheath and the subsequent effect of the velocity filter. The ion dispersions explained by sunward convection over the polar cap are preferentially observed when Bz>0, and over the summer hemisphere. In this case their localization implies that the poleward boundary of the cusp is directly connected to a region of dayside merging between the IMF and the tail lobe field lines. We also present a statistical study of the position of the cusp boundaries and their relation to Bz and AE. Cross-correlation analysis shows that the best correlation with both AE and Bz is obtained when the ion precipitation in the cusp is organized with ion dispersions. The boundary directly linked to the plasma entry/reconnection region, equatorial for Bz < 0, polar for Bz > 0, is most strongly correlated with Bz shifted 30-40 minutes in time. Under the same conditions, the correlation with the instantaneous AE index is also very strong. Finally we suggest that the cusp position is only indirectly controlled by Bz, with a delay of about 40 minutes necessary for establishing a new convection system and stable ionospheric currents inside the magnetosphere.