  Previous observations have shown that, during Martian dust storms, the peak
of the ionosphere rises in altitude. Observational studies of this type,
however, have been extremely limited. Using 13 years of ionospheric peak
altitude data from the Mars Advanced Radar for Subsurface and Ionosphere
Sounding (MARSIS) instrument on Mars Express, we study how the peak altitude
responded to dust storms during six different Mars Years (MY). The peak
altitude increased $\sim$10-15 km during all six events, which include a local
dust storm (MY 33), three regional regional dust storms (MYs 27, 29, and 32),
and two global dust storms (MYs 28 and 34). The peak altitude's orbit-to-orbit
variability was exceptionally large at the apexes of the MY 29 and MY 32 dust
seasons, and dramatically increased during the MY 28 and MY 34 global dust
storms. We conclude that dust storms significantly increase upper atmospheric
variability, which suggests that they enhance dynamical processes that couple
the lower and upper atmospheres, such as upward propagating gravity waves or
atmospheric tides.
