Vortex-like Structure in the Cusp–Magnetosheath Interface

Two-point observations by the INTERBALL satellite pair unveiled a presence of a large vortex-like structure filled by slow and heated plasma in the outer cusp during periods of the positive BZ interplanetary magnetic field (IMF) component. We have found the rotation of the magnetic field and the decrease of its magnitude connected with the presence of a hot plasma population inside the vortex. We found that this structure exhibits a clear reversal of the plasma flow caused by reconnection tailward of the cusp which turns a part of the magnetosheath plasma into the cusp. We discuss the way of a formation such structure. The statistical results have confirmed that this phenomenon is a regular feature of the highaltitude cusp, however, this relatively small structure cannot be observed too often.