Energetic ions (E>35 keV) at 90¿ to the magnetic field line are measured on ISEE-3 in the distant geomagnetic tail and are used as tracers of the particle density during two encounters with the plasma sheet at 210 and 128 earth radii from the earth. Because of the finite gyroradius (2400 km) of these (assumed) protons, different orientation about the magnetic field measure the intensity of different locations, allowing a separation of spatial from temporal variations. Density contour maps of the plasma hseet are constructed, demonstrating the wavy nature of this regime, as well as the existence of density layers within it. |