Long-Term Climate Trends in foF2 at Mid- and High-Latitudes

Climate trends in the upper atmosphere can be driven by a number of factors, including greenhouse gas emissions, changes in lower atmospheric forcing, secular variations in the Earth’s magnetic field, and long-term solar and geomagnetic activity. At mid latitudes, climate trends in the ionosphere are well-studied; however, at high latitudes, complex chemistry and dynamics, as well as lack of long-term ionosonde data and the strong influence of the magnetic field geometry, presents challenges in evaluating these trends. This study evaluates long-term trends in foF2 data from model output of the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM) and the Whole Atmosphere Community Climate Model with thermosphere and ionosphere extensions (WACCM-X) for the period 1950 – 2022, alongside observational foF2 data from the high-latitude Resolute Bay ionosonde and the mid-latitude Chilton ionosonde. Data is compared to model runs from the NeQuick, which includes no drivers of climate change in the upper atmosphere and a static magnetic field configuration. A linear regression approach is applied to remove the long-term effects of the solar cycle; preliminary results from ionosonde data indicate that, at high latitudes, climate trends are consistently positive and statistically significant at the 95% confidence interval when averaged across all local times and months, while at mid latitudes, climate trends from ionosonde data are always negative across all hours of day, and largely negative across all months of the year. TIE-GCM and WACCM-X demonstrate significantly different results, with both positive and negative trends exhibiting some seasonal and local time dependence; this discrepancy indicates further research is necessary into the physical processes governing climate trends in the upper atmosphere to improve model output, particularly at high latitudes.