INTERBALL tail observations of dayside magnetopause oscillations and simultaneous POLAR cusp measurements

On April 13, 1996, while Russia's Interball Tail spacecraft was travelling through the dayside magnetosheath, NASA's Polar spacecraft traversed the no rthern cusp. Observed transients seen in the SCA-1 Interball Tail data are shown to be multiple crossings of the magnetopause. Analysis of the moments data from the SCA-1 instrument and magnetic field data from the MIF instru ment on Interball Tail show quasi-periodic motion of the magnetopause. Simu ltaneous observations of changes in the He2+/H+ density ratio in the cusp b y the Polar/TIMAS instrument show variations on the same time scale. We con clude that the variations in cusp data observed by Polar are the result of changes in the reconnection rate at the magnetopause and that these changes are associated with the magnetopause oscillations observed by Interball.