Photochemistry vs. dynamo as drivers of day-to-day variability in the ionosphere

Ionospheric variability is driven locally by a combination of electrodynamical and photochemical processes. Such processes are important in the context of the forcing of the ionosphere “from below,” as they represent the end points of two distinct coupling pathways by which wave activity in the lower, neutral atmosphere impacts the ionosphere above. Here, we quantify the short-term variability of the ionosphere sourced by forcing from below using observational data from the Ionospheric Connections Explorer (ICON) and the Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM-X.) We find that electron density variance that is driven by forcing from below is, on average, ~60% weaker than the variance that is sourced by geomagnetic sources (“from above.”) We further quantify the relative contributions of electrodynamics and photochemistry to ionospheric variability by both correlating the ratio of atomic oxygen to molecular nitrogen and ion drifts to electron densities in the E- and F-regions. We are able to attribute approximately 20% of the variance in electron density to photochemistry in the daytime F-region, with a more significant (~40%) contribution during nighttime.