Homogeneous nucleation on Mars. An unexpected process that deciphers mysterious elongated clouds

Homogeneous nucleation is generally not considered a possibility in cloud formation processes in the atmosphere of Mars (Määttänen et al. 2005; Clancy et al., 2017), or Earth (Pruppacher & Klett, 1996), as it requires high levels of supersaturation that are considered unlikely to occur under real atmospheric conditions, in which heterogeneous nucleation on widespread aerosols depletes water in excess of saturation.

The Arsia Mons Elongated Cloud (AMEC) is an eye-catching and mysterious cloud occurring recurrently every morning during the dusty season over the Arsia Mons volcano on Mars (Hernández-Bernal et al., 2021). It shows a peculiar elongated shape that in only 3 hours expands up to 1800 km from its origin point. Hernández-Bernal et al. (2022) investigated this cloud based on the LMD Mars Mesoscale model (Spiga and Forget, 2009). The tail of the cloud was not reproduced in the model, but a cold pocket with temperatures down to 30K below the environment and supersaturation up to 105 appeared next to Arsia Mons, in a position, altitude, and local time and season coincident with the origin point of the AMEC in observations.

In this work we show that these are conditions conductive to homogeneous nucleation, and when we introduce this process as a new cloud formation process in the LMD Mars Mesoscale model, we obtain a good representation of the AMEC, and its long tail. This provides an excellent explanation for this mysterious cloud and shows that homogeneous nucleation is possible and can have significant effects in the atmosphere of Mars. We intend to explore these and other clouds on Mars and Earth possibly involving homogeneous nucleation.

 

References:

• Clancy, R., Montmessin, F., Benson, J., Daerden, F., Colaprete, A., & Wolff, M. (2017). Mars Clouds. In R. Haberle, R. Clancy, F. Forget, M. Smith, & R. Zurek (Eds.), The Atmosphere and Climate of Mars (Cambridge planetary science (pp. 76–105). Cambridge: Cambridge University Press. https://doi.org/10.1017/9781139060172.005 
• Määttänen, A., Vehkamäki, H., Lauri, A., Merikallio, S., Kauhanen, J., Savijärvi, H., & Kulmala, M. (2005). Nucleation studies in the Martian atmosphere. Journal of Geophysical Research: Planets, 110(E2). https://doi.org/10.1029/2004JE002308 
• Hernández‐Bernal, J., Sánchez‐Lavega, A., del Río‐Gaztelurrutia, T., Ravanis, E., Cardesín‐Moinelo, A., Connour, K., ... & Hauber, E. (2021). An extremely elongated cloud over Arsia Mons volcano on Mars: I. Life cycle. Journal of Geophysical Research: Planets, 126(3), e2020JE006517. https://doi.org/10.1029/2020JE006517 
• Hernández‐Bernal, J., Spiga, A., Sánchez‐Lavega, A., del Río‐Gaztelurrutia, T., Forget, F., & Millour, E. (2022). An extremely elongated cloud over Arsia Mons volcano on Mars: 2. Mesoscale modeling. Journal of Geophysical Research: Planets, 127(10), e2022JE007352. https://doi.org/10.1029/2022JE007352 
• Pruppacher, H. R., Klett, J. D., & Wang, P. K. (1996). Microphysics of clouds and precipitation. Springer Science. https://doi.org/10.1007/978-0-306-48100-0 
• Spiga, A., & Forget, F. (2009). A new model to simulate the Martian mesoscale and microscale atmospheric circulation: Validation and first results. Journal of Geophysical Research: Planets, 114(E2). https://doi.org/10.1029/2008JE003242