Has the ionospheric F2 region changed permanently during the last thirty years?

Abstract

A cooling of 50 K in the thermosphere has been predicted by Roble and Dickinson (1989) due to doubling of CO₂. This cooling is expected to produce some permanent changes in the ionospheric F2 region. We have examined 32 years of F2 layer critical frequency (foF2) data for three ionospheric stations namely Boulder, Washington D.C. and Moscow. No significant longterm changes in foF2 could be identified. This is not a surprising result because CO₂ has increased only by about 15% during this period. Even a doubling of CO₂ would lower the F2 layer peak only by about 20 km, with a small change in the F2 layer electron density (Rishbeth 1990). We conclude that no detectable permanent change has yet occurred in the F2-layer during the last thirty years. However, when CO₂ doubles over its 1960 value in the 21st century, it might be possible to identify some permanent changes, especially in the height of the F2 layer peak.