Contribution to ionospheric F2 region long-term trend studies through seasonal and diurnal pattern analysis

Abstract

The ionosphere´s long-term trends have been studied since 1989, with a particular focus on the F2 region´s parameters due to their importance in space weather and radio signal propagation research. The accuracy and attribution of trends, particularly for the critical frequency foF2, have been controversial due to methodological issues and identification of the sources, such as greenhouse gases concentration increase, natural forcings, or a combination of them. The present work analyzes these current concerns by considering foF2 measured at mid-to-low latitude stations across the globe covering up to the most recent full year, 2022. Seasonal and diurnal variability of the trends were assessed by analyzing the relative roles of two potential drivers: increasing greenhouse gases concentration and geomagnetic field secular variation using a simple theoretical analysis. The results show overall negative trends with the most negative values around equinox and the weakest, or slightly positive trends in December–February or June–August, respective of the winter hemisphere. The general diurnal pattern evinces the most negative values in daytime hours and the weakest during nighttime. Studying and understanding these trends and their possible sources will contribute to the broader research area of climate change, which is taking place in all the layers of the Earth´s atmosphere.