A modelling study is presented which investigates in-situ generated changes of the thermosphere and ionosphere during a solar eclipse. Neutral temperatures are expected to drop by up to 40 ¿K at 240 km height in the totality footprint, with neutral winds of up to 26 m/s responding to the change of pressure. Both temperatures and winds are found to respond with a time lag of 30 min after the passing of the Moon's shadow. A gravity wave is generated in the neutral atmosphere and propagates into the opposite hemisphere at around 300 m/s. The combined effects of thermal cooling and downwelling lead to an overall increase in [O>, while [N2> initially rises and then for several hours after the eclipse is below the steady state level. An enhancement of [NmF2> is found and explained by the atmosphere's contraction during, and the reduced [O>/[N2> ratio after the eclipse. ¿ 1998 American Geophysical Union