Incoherent scattering from the collision dominated D-region. Comparison of theories with experimental data

There has been a long standing controversy as to the introduction of the collisional term in the incoherent scattering theory. This has profound implications in interpreting the incoherent scatter spectra from the collision dominated D- and E-regions. Among the different theoretical formulations, those by Dougherty and Farley and Waldteufel have been used for the interpretation of incoherent scatter data. Waldteufel's formulation apparently improves on the theoretical model of Dougherty and Farley by allowing for momentum conservation and temperature changes during collisions.Using incoherent scatter data from D-region heights over Arecibo we show for the first time that Dougherty and Farley's formulation is the correct one. This is due to the fact that during a collision ions lose both momentum and energy to neutrals and so far as the ion gas is concerned, neither should be conserved.Once the correct formulation has been established, it can be seen that the incoherent scatter technique offers a unique advantage in inferring mesospheric parameters with very high precision. For example, the ratio of the number density to neutral temperature in the D-region over Arecibo could be measured to accuracies of a few per cent. The results of such measurements are in excellent agreement with the CIRA 1972 model and show a day-to-day variability limited to within 10–15%.