Influence of the IMF Sector Structure on the Latitude of the Daytime Cusp Region

The particle data from DMSP F7 spacecraftt for January, July and December 1984 were used to examine the influence of the IMF Bx and By components on the latitude of the cusp equatorward boundary in the northern and southern hemispheres. To exclude the effects of magnetic activity the difference ΔΦ between observed latitude of the cusp equatorward boundary Φobs and model cusp boundary Φmod is used for analysis, where Φmod is latitude of the equatorward boundary corrected for effects of AE and Dst-indices: Φmod=0.010- Dst-0.010. AE+77.7 [Eather, 1985]. The evident dependence of the cusp position on sign and value of the IMF Bx and By components is shown. During December/January period the cusp boundary for conditions By>0, Bx 0. The quite opposite regularity is observed during July period. The sense of displacement is the same in the northern and southern hemispheres. Using the data about the analogous effects for the main ionospheric trough located on the equatorward boundary of the nighttime auroral oval, the conclusion is made that the oval in the both hemispheres displaces as a whole under influence of the sector structure.