In an ionospheric depletion experiment where chemically reactive vapors such as H2O and CO2 are injected into the O+ dominant F region to accelerate the plasma recombination rate and to reduce the plasma density, the ion composition in the depleted region is modified, and photometric emissions are produced. We compare in situ ion composition, density, and photometric measurements from two ionospheric depletion experiments with predictions from chemical modeling. The two injections, Waterhole I and III, were part of an auroral perturbation experiment and occurred in different ambient conditions. In both injections a core region of greater than fivefold plasma depletion was observed over ≈5-km diameter within seconds of the injection, surrounded by an outer region of less drastic and slower depletion. In Waterhole I the plasma density was depleted tenfold over a 30-km diamter region after 2 min. The ambient O+ density was drastically reduced, and the molecular O+2 abundance was enhanced fivehold in the depletion region. OH airglow emission associated with the depletion was observed with a peak emission intensity of ≈1 kR. In Waterhole III the ambient density was a decade lower, and the plasma depletion was less drastic, being twofold over 30 km after 2 min. The airglow emissions were also much less intense and below measurement sensitivity (30 R for the OH 306.4-nm emission; 50 R for the 630.0-nm emission).

In the chemical model the major ion chemical production and loss processes in the injection are considered, and the continuity equations for major ion and airglow-producing species are solved numerically to simulate the temporal-spatial profiles of plasma depletion, ion composition, and airglow emissions. The simulations indicate that the overall depletion rates in different parts of the depletion region are governed by different parameters.