P036-06
A long term study of twilight clouds on Mars based on Mars Express VMC images

Thursday, 10 December 2020: 05:50
Virtual
Jorge Hernandez-Bernal1, Agustin Sanchez-Lavega1, Teresa del Rio - Gaztelurrutia2, Ricardo Hueso3, Eleni Ravanis4, Alejandro Cardesín-Moinelo4, Simon Wood5 and Dmitri V. Titov6, (1)University of the Basque Country, Donostia, Spain, (2)University of the Basque Country UPV/EHU, Bilbao, Spain, (3)University of the Basque Country, Fisica Aplicada I, Donostia, Spain, (4)European Space Agency, ESAC, Madrid, Spain, (5)European Space Agengy, ESA-ESOC, Darmstadt, Germany, (6)ESA-ESTEC, Noordwijk, Netherlands
Recorded Presentation
Abstract:
During twilight, when the sun is below the horizon, clouds and atmospheric dust can still be illuminated by the sun if they are high enough over the surface, as they escape the shadow of the planet. Observations of this direct illumination can be used to determine the minimum altitude for elevated features. Twilight clouds were first observed on Mars by ground-based telescopes, and then by cameras on the Viking orbiters. However, in the last few decades of Mars exploration, most orbiters have been placed in sun-synchronous orbits centered around the afternoon, and thus few observations of the twilight have been collected.

Mars Express is an excellent platform for the study of twilight clouds due to its non-sun-synchronous orbit, The Visual Monitoring Camera (VMC) onboard MEX has a wide Field of View that allows regular observations of the full disk of Mars (usually including the region in dawn) from the apocenter of the MEX orbit. The current VMC dataset includes ~50 000 images distributed across ~3000 observations (each observation consisting of several consecutive images), covering 8 Martian Years. We have developed a pipeline to perform a the systematic study of twilight clouds in VMC images.

We find three main groups of recurrent of twilight clouds in a belt around 45ºS. These three groups correspond to the regions of Terra Cimmeria, Terra Sirenum, and Aonia Terra, where the clouds appear mostly in the southern winter. Additionally, some of the highest clouds we find correspond to these regions.

Whilst we find that these twilight clouds are more common during the Aphelion Cloud Belt season (ACB), the latitudinal distribution of clouds differs from that of the ACB, as the biggest concentration of twilight clouds happens in a belt around 45ºS, while the ACB is more or less symmetrical around the equator. This may be explained by the fact that VMC observations are mostly in the early morning, while most ACB studies have been focused on the afternoon. Our results are biased by the fact that we only detect isolated clouds at some altitude over the surface, and that might also be part of the explanation for this discrepancy.

<< Previous Abstract | Next Abstract >>