Daily dust variation from the PFS MEx observations

We collected over 7 Martian years (MY) of data observed by the Planetary Fourier Spectrometer (PFS) to present a daily variation of dust content in the Martian atmosphere. We found three typical behaviors of dust opacities with LT (local time). The most peculiar variation was observed when global dust storms (MYs 28 and 34) or particularly strong regional storms (MY 29) occurred on Mars. Here, large dust opacities were measured at 10 LT (MY 34) and 11 LT (MY 28). Then, relatively small values of dust opacities were found in the evening (20 LT). The non-dusty season, particularly near northern summer solstice, was characterized by a deep minimum of the total dust opacity at late night/early morning, while small variations around the mean value were observed during daytime. The clear trend of dust was observed over both hemispheres during early morning. We noted elevated dust opacities in the second half of the year compared to the non-dusty season in all Martian years without global dust storms. The daily variation of three types of storms occurring in moderately dusty conditions was also investigated. Dust in A storms was present in the atmosphere at all LTs and was mostly confined to the southern hemisphere. The maximum of dust opacities in B storms was found at 15–17 LT, close to the South Pole. C storms were mainly constrained to southern latitudes and occurred from the late morning to midday. •During global storms, we observe large dust opacities before midday compared to values of dust opacity in the evening.•Close to aphelion, dust opacities have a minimum at night/early morning.•Close to aphelion, small variations around the mean value of dust opacities are observed during daytime.•No special trend in variation of dust opacities with LT (local time) is found in a typical dusty season.