Abstract
Abstract. The principal optical observable emission resulting from ionospheric modification (IM) experiments is the atomic oxygen red line at 630 nm, originating from the O(1D–3P) transition. Because the O(1D) atom has a long radiative lifetime, it is sensitive to collisional relaxation and an observed decay faster than the radiative rate can be attributed to collisions with atmospheric species. In contrast to the common practice of ignoring O-atoms in interpreting such observations in the past, recent experimental studies on the relaxation of O(1D) by O(3P) have revealed the dominant role of oxygen atoms in controlling the lifetime of O(1D) at altitudes relevant to IM experiments. Using the most up-to-date rate coefficients for collisional relaxation of O(1D) by O, N2, and O2, it is now possible to analyze the red line decays observed in IM experiments and thus probe the local ionospheric composition. In this manner, we can demonstrate an approach to remotely detect O-atoms at the altitudes relevant to IM experiments, which we call remote oxygen sensing by ionospheric excitation (ROSIE). The results can be compared with atmospheric models and used to study the temporal, seasonal, altitude and spatial variation of ionospheric O-atom density in the vicinity of heating facilities. We discuss the relevance to atmospheric observations and ionospheric heating experiments and report an analysis of representative IM data.
Highlights
It has been a prime goal of optical aeronomy to make remote measurements of atmospheric emissions and deduce the atomic and molecular composition of the region being observed
Recent laboratory measurements at SRI International have established that the removal rate coefficients for O(1D)+N2 and O(1D)+O are comparable and O atoms play a significant role in the ionospheric O(1D) decay (Closser, 2005; Kalogerakis, 2005, 2006; Slanger, 2006)
We present the relevant background to this approach, explore selected existing data sets from representative ionospheric modification (IM) sites, determine the O-atom densities implied from the observed decays, and discuss the validity and relevance of this approach as a remote sensing technique for ionospheric O-atom densities
Summary
It has been a prime goal of optical aeronomy to make remote measurements of atmospheric emissions and deduce the atomic and molecular composition of the region being observed. The temporal evolution of the return to equilibrium in these experiments provides information on collisional loss, where the significant collider species are molecular nitrogen and oxygen atoms, the latter predominating above ∼200 km. The lack of reliable information on the collisional role of O-atoms has often led to the assumption that the red line decay was controlled by collisions with N2. Recent laboratory measurements at SRI International have established that the removal rate coefficients for O(1D)+N2 and O(1D)+O are comparable and O atoms play a significant role in the ionospheric O(1D) decay (Closser, 2005; Kalogerakis, 2005, 2006; Slanger, 2006). (8.0±7.0)×10−12 Rate coefficient insignificant 1×10−11 (1000 K) 6.9×10−12 (1000 K) 7.8×10−12 (1000 K) 9.2×10−13 (750 K) Rate coefficient insignificant (2.2±0.6)×10−11 (300 K)
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