Long-Term Trends in the D- and E-Region Based on Rocket-Borne Measurements

Electron densities obtained from rocket borne measurements are compared to an empirical, steady state model built from these data. The ratios between each measured value and its corresponding model value vs. time yield trends which significantly vary with altitude. Notably above 120–130 km the electron densities generally increase, whereas between 95 and 120 km the ionosphere appears stable. Somewhere below 80–90 km - depending on the investigated data subset - there is again a positive trend down to below 70 km. Tentative explanations such as cooling of the mesosphere are suggested and may be confirmed by comprehensive theoretical models of the upper atmosphere.