| 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 recent work, we showed that in contrast to the common practice
of neglecting oxygen atoms in interpreting such observations in the past, O atoms control the
atomic oxygen red line emission between approximately 200 and 300 km [1]. Therefore, the
observed O(1D) lifetime in IM experiments provides a measure of the local O-atom
density. An analysis of existing IM data yields good agreement between observations
and the MSIS model for altitudes above 250 km. In this report, we focus on the
interpretation of the temporal evolution of the atomic oxygen red line emission
at high and low altitudes. We discuss the relevance to atmospheric observations
and ionospheric heating experiments and report an analysis of representative IM
data.
This work is supported by the CEDAR Program of the U.S. National Science Foundation
(NSF) under grant no. ATM-0737713.
[1] Kalogerakis, K. S., Slanger, T. G., Kendall, E. A., Pedersen, T. R., Kosch, M. J.,
Gustavsson, B., Rietveld, M. T., “Remote Oxygen Sensing by Ionospheric Excitation
(ROSIE),” Ann. Geophys. 27, 2183-2189 (2009). |