Variations in the Ionospheric Peak Altitude at Mars in Response to Dust Storms: 13 Years of Observations from the Mars Express Radar Sounder
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.