Mesoscale modeling of the Arsia Mons Elongated Cloud (AMEC) on Mars

A recent work (Hernández-Bernal et al., 2021) described the Arsia Mons Elongated Cloud (AMEC), an impressive orographically generated cloud that appears next to the Arsia Mons volcano on Mars during the early morning on a daily basis in southern spring and summer. The most visually striking characteristic of this cloud is its extremely elongated shape.

This spectacular cloud is formed by underlying dynamical and microphysical processes that remain to be elucidated. To that end, we run the LMD (Laboratoire de Météorologie Dynamique) MMM (Mars Mesoscale Model; Spiga and Forget, 2009) for Solar Longitude 270º, with a grid resolution of 10km. The model shows that the interaction of fast transient easterly winds with the summit of Arsia Mons results in strong ascending winds on the western slope of the volcano, seasonally and diurnally coincident with the occurrence of the AMEC according to observations. These ascending winds propagate vertically and result in a temperature drop which takes values of down to -30K in the hygropause (around 45 km over the areoid). This results in extreme relative humidity values and condensation, spatially coincident with what Hernández-Bernal et al. (2021) called the head of the AMEC. We expect advection by easterly winds to produce the particular elongated shape of the AMEC, however the advection of condensed particles is not clearly reproduced by the model.

This AMEC study demonstrates that coupling the analysis of mesoscale modeling with imagery monitoring on elongated clouds help to better understand the involved processes to form the cloud. We aim to search for similar mechanisms in other visually resemblant clouds, like those reported by Clancy et al. (2006; 2021), and others observed by the Visual Monitoring Camera onboard Mars Express, among other imagers. In the meantime, the AMEC is expected to appear again in early June 2022 and different instruments are already planning observations.

References:

• Hernández‐Bernal, Jorge, et al. "An extremely elongated cloud over Arsia Mons volcano on Mars: I. Life cycle." Journal of Geophysical Research: Planets 126.3 (2021): e2020JE006517.
• Spiga, Aymeric, and François Forget. "A new model to simulate the Martian mesoscale and microscale atmospheric circulation: Validation and first results." Journal of Geophysical Research: Planets 114.E2 (2009).
• Clancy, R. Todd, et al. "Valles Marineris cloud trails." Journal of Geophysical Research: Planets 114.E11 (2009).
• Clancy, R. Todd, et al. "Mars perihelion cloud trails as revealed by MARCI: Mesoscale topographically focused updrafts and gravity wave forcing of high altitude clouds." Icarus 362 (2021): 114411.