Model simulations of global change in the ionosphere

Observations of secular trends in the E and F₁ regions of the ionosphere indicate that electron densities have increased, and that the height of the E-region peak has decreased, during the past several decades. Detection of trends in the upper ionosphere through analysis of F₂-layer parameters has been more complex and controversial. In order to facilitate observational detection of long-term trends in the ionosphere, simulations were performed using a single-column upper atmosphere model. CO₂ concentrations for the year 2000 and projected for the year 2100 were used to investigate changes of electron densities and the altitudes of ionospheric layers. Results show that increased CO₂ concentration increases electron density in the lower regions of the ionosphere, but decreases electron density in the upper ionosphere. The transition altitude occurs slightly below the F₂ peak altitude (h_mF₂). The proximity of h_mF₂ to the transition altitude may explain why different analyses of long-term trends in F₂ peak density have shown both positive and negative trends. The altitudes of the E, F₁ and F₂ regions all decrease with increased CO₂ concentration.