A. Spiga

Parameterization of Rocket Dust Storms on Mars in the LMD Martian GCM: Modeling Details and Validation

The origin of the detached dust layers observed by the Mars Climate Sounder aboard the Mars Reconnaissance Orbiter is still debated. Spiga et al. (2013, https://doi.org/10.1002/jgre.20046) revealed that deep mesoscale convective “rocket dust storms” are likely to play an important role in forming these dust layers. To investigate how the detached dust layers are generated by this mesoscale phenomenon and subsequently evolve at larger scales, a parameterization of rocket dust storms to represent the mesoscale dust convection is designed and included into the Laboratoire de Météorologie Dynamique (LMD) Martian Global Climate Model (GCM). The new parameterization allows dust particles in the GCM to be transported to higher altitudes than in traditional GCMs. Combined with the horizontal transport by large-scale winds, the dust particles spread out and form detached dust layers. During the Martian dusty seasons, the LMD GCM with the new parameterization is able to form detached dust layers. The formation, evolution, and decay of the simulated dust layers are largely in agreement with the Mars Climate Sounder observations. This suggests that mesoscale rocket dust storms are among the key factors to explain the observed detached dust layers on Mars. However, the detached dust layers remain absent in the GCM during the clear seasons, even with the new parameterization. This implies that other relevant atmospheric processes, operating when no dust storms are occurring, are needed to explain the Martian detached dust layers. More observations of local dust storms could improve the ad hoc aspects of this parameterization, such as the trigger and timing of dust injection. Plain Language Summary On Mars, dust is of major importance to the Martian atmosphere, analogous to the importance of water to the Earth’s atmosphere. But unlike the water on Earth, the distribution of dust on Mars is still not well understood, particularly the vertical distribution. The Mars Climate Sounder aboard the Mars Reconnaissance Orbiter found that the dust on Mars is detached at ∼20–40 km in altitude in the Martian atmosphere, rather than concentrated in the near-surface atmosphere and decreasing as the pressure decreases, as scientists have thought since the 1980s. The reason for the detached dust layers is still debated. In this paper, we implemented a modeling study by simulating the small-scale deep rocket dust storm in a Global Climate Model to explore the origins of the detached dust layers. We found that when the Global Climate Model included rocket dust storms, the simulations produced the detached structures of dust on Mars. This suggests that the rocket dust storm is responsible for the formation of the detached dust layers. Meanwhile, the rocket dust storms cannot reproduce all the detached dust layers observed by Mars Climate Sounder. This implies that some unknown atmospheric processes can also contribute to the existence of the detached dust layers.