Simultaneous polar cap and magnetotail observations of intense polar rain

Six prolonged episodes of intense polar rain with average or above average temperatures occurred during the four-month period from mid-February to mid-June 1978. Electrons with energies up to 1 keV are observed throughout these events, and 9-keV electrons occasionally are detected. To investigate whether this intense polar rain is accelerated within the magnetosphere, we compare DMSP F2 electron measurements made at low altitudes over the polar cap with near-simultaneous ISEE 1 electron measurements made in the northern tail lobe at distances between 10 and 22.6 R/sub E/. In some cases, the electron spectra measured at low altitude are nearly identical to those measured in the tail lobe. In other cases, intensities are similar, but the phase space densities measured by DMSP exceed those measured by ISEE at energies above 500 eV. The episodes with extremely similar spectra show that intense polar rain can pass through the tail lobes without undergoing acceleration between 22.6 R/sub E/ and 800 km altitude. Three-dimensional ISSE measurements of electron distribution functions suggest that the field-aligned pitch angle anisotropy of the tail lobe electron population may account for most if not all of the differences when the spectra do not match