Articles | Volume 33, issue 4
Regular paper
08 Apr 2015
Regular paper |  | 08 Apr 2015

Global variation in the long-term seasonal changes observed in ionospheric F region data

C. J. Scott and R. Stamper

Abstract. Long-term variability has previously been observed in the relative magnitude of annual and semi-annual variations in the critical frequency (related to the peak electron concentration) of the ionospheric F2 layer (foF2). In this paper we investigate the global patterns in such variability by calculating the time varying power ratio of semi-annual to annual components seen in ionospheric foF2 data sequences from 77 ionospheric monitoring stations around the world. The temporal variation in power ratios observed at each station was then correlated with the same parameter calculated from similar epochs for the Slough/Chilton data set (for which there exists the longest continuous sequence of ionospheric data). This technique reveals strong regional variation in the data, which bears a striking similarity to the regional variation observed in long-term changes to the height of the ionospheric F2 layer. We argue that since both the height and peak density of the ionospheric F2 region are influenced by changes to thermospheric circulation and composition, the observed long-term and regional variability can be explained by such changes. In the absence of long-term measurements of thermospheric composition, detailed modelling work is required to investigate these processes.

Short summary
We use a novel technique to infer long-term compositional changes to the thermosphere from the annual variation of the ionospheric F2 region. A global analysis of these data reveal that long-term changes differ between geographic locations in a way that is very similar to the observed variation in the ionospheric response to increased atmospheric CO2 levels. In the absence of long-term measurements of thermospheric composition, further, detailed, modelling work is required.