Erosion of the inner magnetosphere during geomagnetic storms

Using the empirical magnetic field model dependent on the Dst index and solar wind dynamic pressure, we calculated the behaviour of the contour B=B-S in the equatorial plane of the magnetosphere where B-S is the magnetic field in the subsolar point at the magnetopause. The inner domain of the magnetosphere outlined by this contour contains the bulk of geomagnetically trapped particles. During quiet time the boundary of the inner magnetosphere passes al the distance similar to 10R(E) at noon and at similar to 7R(E) at midnight. During very intense storms this distance can be reduced to 4-5R(E) for all MLT. The calculation results ag ree well with the satellite measurements of the magnetopause location during storms, The ionospheric projection of the B = B-S contour calculated with the Euler potential technique is close to the equatorward edge of the auroral oval.