Residual ionization in the polar lower ionosphere

S>Turbulent scattering of 2.3 Mc/s radio waves is found to persist throughout the polar night between altitudes of 80 and 100 km at a geomagnetic latitude of 79 deg S. Residual electron densities are estimated to increase from 5/cm/sup 2/ at 80 km to 1 or 2 x 10/sup 2/ between 90 and 100 km. Transport processes are unable to maintain these concentrations, though tarbulent transport may assist. Present estimates of electron loss rates require ionization rates in excess of cosmic-ray production. An equivalent vertical flux of protons of 0.2 < E < 4 Mev energy and density up to 170/cm/sup 2/ sec, or, alternatively, of electrons with 10 kev < E < 100 kev and denstty about 70/cm/sup 2/ sec, is called for. Time variations associated with solar protons and Forbush decreases of cosmic radiation suggest that protons are responsible. (auth)