Initial results from the POLAR magnetic fields investigation

The POLAR magnetic field investigation was designed to provide a high temporal resolution and high sensitivity measurement of the magnetic field along the POLAR orbit from perigee at 2 R _E to apogee at 9 R _E . The objectives of the investigation include probing the field aligned currents that couple the solar wind interaction and the tail dynamics to the auroral ionosphere. The launch of the spacecraft on February 24, 1966 was nominal and the turn on of the instruments very successful. Comparisons with Tsyganenko's 1995 model of the external current systems show that at quiet times it reproduces the field well. POLAR is clearly observing the field aligned current systems and the ring current. On one occasion when the IMF was strongly northward and the solar wind dynamic pressure stronger than usual the high altitude, high latitude magnetosphere became filled with magnetosheath type plasma. This event was probably an encounter with the polar cusp near the cusp-magnetosheath interface.