Ionospheric O~+ Momentum Balance Through Charge ExchangeWith Thermospheric O Atoms

摘要

One of the most notorious uncertainties in ionosphere/thermosphere physics concerns the cross section for resonant charge exchange between neutral atomic and ionized oxygen, O and O~+, the principle constituents between ～200–500 km in the terrestrial atmosphere. O ? O~+ charge exchange plays a vital role in both momentum and energy exchange between the thermosphere and ionosphere, such that the value of the cross section, Q_(O?O~+) , strongly influences calculations of plasma drift speeds, diffusion coefficients, and electron density distributions. We present an analysis of the nighttime O~+ momentum budget in the F region ionosphere, using an unprecedented 27-year baseline of observations from Arecibo Observatory, as a means to assess the agreement between the data, recent theoretical calculations of Q_(O?O~+) , and NRLMSISE-00 model predictions of O density, [O]. We find evidence for local time, seasonal, and solar cycle variation between the derived and modeled O ? O~+ collision frequency, with the best agreement observed near midnight at solar maximum. The data overall support our conclusion that recent theory regarding the magnitude of Q_(O?O~+) is likely accurate. Although biases in the momentum balance technique may account in part or in full for the local time and seasonal dependencies in observed O~+ momentum imbalances, the most likely source of the observed solar cycle variation is MSIS model underestimation of [O]. These findings serve to establish the O~+ momentum and energy balance techniques as a valuable means of remotely sensing thermospheric [O] in support of future model validation and development.