The adequacy of the ionospheric source in supplying magnetospheric plasma

More than 30 years after the prediction of the polar wind outflow from the high latitude ionosphere, the exact magnitude and ultimate fate of the iono spheric plasma supply remains unknown. Estimates made more than a decade ag o suggested that the polar ion outflow might well be of sufficient strength to populate the different regions of the Earth's magnetosphere. Direct mea surements in the high altitude magnetosphere became possible only with the launch of the Polar spacecraft. The combination of the Thermal Ion Dynamics Experiment and the Plasma Source Instrument has revealed the presence of l ow energy (<10 eV) ions moving through the polar regions and into the lobes of the magnetotail, These ions would have been invisible to previous un-ne utralized satellites because of the high positive spacecraft potentials. Th rough the use of a recently developed single particle trajectory and energi zation code, the movement and energy transformation of these measured parti cles can be estimated. They are found to move into the plasma sheet region and to be energized to typical plasma sheet energies. The magnitude of the flux of the highly variable out-flowing ions mapped to 1000 km altitude is 1 - 3 x 10(8) ion/cm(2) s in agreement with the original estimates. Future observations by the TIDE/PSI instruments will be required to determine the extent of the total ionospheric contribution. (C) 2000 Elsevier Science Ltd . All rights reserved.