The 2018 Planet-Encircling Dust Storm: Effects on the Mars Upper Atmosphere as seen in MAVEN Accelerometer Data

This summer a planet-encircling dust event (PEDE) bloomed on Mars, the first such storm since 2007. As the dust haze spread into the middle atmosphere, temperatures there increased substantially, particularly on the dayside due to solar heating of the dust and to adiabatic warming as the atmospheric circulation adjusted to the PEDE evolution. During this development, captured with good time resolution by the Mars Color Imager and the Mars Climate Sounder onboard the Mars Reconnaissance Orbiter, the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission was observing the response of the upper atmosphere to the activity lower down.

As the middle atmosphere warmed, densities at higher altitudes increased hydrostatically, and this was seen by the MAVEN accelerometers, tracking of the spacecraft by the navigation team, and by other instruments onboard, including the in situmeasurements of the MAVEN Neutral Gas and Ion Mass Spectrometer (NGIMS). During the PEDE, MAVEN adjusted its periapsis altitude to remain in its nominal operating density corridor, although the team tended to keep periapsis safely in the middle or lower density (higher altitude) portions of the domain (0.05 - 0.1 kg/km³), guarding against a sudden increase in density. The observed density variation in the upper atmosphere was not, however, a simple increase. Large orbit-to-orbit variability probably reflected the non-uniform distribution of the dust in the lower atmosphere, particularly during the early phases of the PEDE. However, the magnitude of the general increase in density and then its more precipitous decline indicate a more complicated picture. Some of the complication was due to the progression of periapsis in local time, moving from the morning terminator into the early morning hours, a time of large orbit-to-orbit variability even at non-PEDE times. This presentation will discuss these variations in density during the PEDE in more detail. The accelerometer data also reveal high-frequency fluctuations in periapsis density that had sizable amplitude during this period. These are being evaluated as possible signatures of enhanced gravity wave propagation from the lower atmosphere during the 2018 PEDE.

Copyright: 2018 California Institute of Technology; Government sponsorship acknowledged.