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ROle and impAct of Dust and clouds in the Martian Atmosphere: from lab to space

Periodic Reporting for period 1 - ROADMAP (ROle and impAct of Dust and clouds in the Martian Atmosphere: from lab to space)

Reporting period: 2020-11-01 to 2021-10-31

RoadMap is a joint scientific project between BIRA-IASB (Belgium), Aarhus Universitet (Denmark), University of Duisburg-Essen (Germany) and CSIC (Spain).

The concept of the RoadMap (ROle and impAct of Dust and clouds in the Martian AtmosPhere) project is defined by an integrated approach of different scientific aspects (laboratory, modelling of specific phenomena, space data analysis, global modelling) in order to improve our vision of the Martian atmosphere and provide a new generation of high-level data which will increase the science return of the past and current missions to Mars, but will also shape and help future planetary missions.

This will be performed through the observation of the Martian atmosphere using existing data to retrieve abundances and properties of gaseous constituents, dust and cloud, through improved analysis tools. These tools will be directly based on measurements carried out in the laboratory. The updated Martian fields will then be used to improve the modelling and understanding of the atmosphere using GCMs (General Circulation Models). The new knowledge will provide input for future Mars missions.

Dust is present everywhere on Mars, yet its abundance, physical properties, size distribution as well as its impact on the composition, structure and dynamics of the atmosphere has today only barely been addressed and understood. The understanding of the mechanisms involved in getting dust from the surface into the atmosphere is of major importance.

Dust is lifted from the surface up into the atmosphere by several processes. Surface wind stress lifting and dust devils are thought to be the primary mechanisms to lift dust. The detachment threshold will depend on the forces induced by the wind shear, the surface adhesion (which inhibits the fine grain removal) and gravitation (which inhibits the larger grain removal). After detachment from the surface, three transport regimes are usually considered: suspension in which the grain remains aloft in the atmosphere, saltation in which the particle will fall back to the surface, and creep in which the particle undergoes rolling and sliding on the surface. When the large particles return to the surface, they impact dust grains which in turn can be injected into the atmosphere.

Dust lifted into the atmosphere will eventually produce clouds and hazes, which can span different spatial scales from local to global, and different timescales from hour to seasons. Dust storms have historically been classified by size as local, regional and global storms. Sometimes, such events evolve into Global Dust Storms with large and long-lasting storms. The processes that control the creation, expansion, and ultimately the decay of global dust storms are likely critically dependent on the radiative–dynamic feedbacks between dust lifting, the heating of the atmosphere, and the circulation, which result in the intensification and/or the spatial expansion of dust lifting.

The dust and water cycles are coupled through cloud condensation processes, but dust also modifies the thermal structure of the atmosphere. Recent studies suggest that global dust storms effectively transport water vapour from the near-surface to the middle atmosphere and increase the escape rate of atmospheric hydrogen. In 2018, a global dust storm occurred on Mars, providing a unique opportunity to study the latitudinal, longitudinal, and temporal variations of the water vapour vertical profile generated by the global dust storm from the new solar occultation measurements by NOMAD/EMTGO. Using different dust and clouds parameters we will improve the retrieval of trace gas and dust from space data, in particular from NOMAD. Also GCM will be updated with the latest results from the lab and the improved lifting, aggregation and radiative models built upon these.
The following describe the work achieved so far for each of the work packages:
WP2. Laboratory measurements
Provide physical properties of airborne martian dust particles based on the best possible martian simulants and based on state-of-the-art laboratory simulations of relevant dust suspension mechanisms. Optical properties by means of light scattering experiments will complement the set of data to describe the physical properties of suspended dust.
Major results:
* Selection of three simulants; preparation of the samples to correspond to different size distributions found on Mars
* Detailed characterization of the samples
* Measurement of the threshold and flux of dust for the first time under martian conditions
* Improved measurements of wind induced dust resuspension and settling time/velocity
* New refractive indexes of different dust size

WP3. Micro-modelling
complement and expand our knowledge of small and fine scale processes through numerical modelling. This work package uses data collected in the lab experiments of WP2 to develop and advance parameterizations of physical processes.
Major results:
* Summary of the lifting and aggregation models existing in the literature and implemented in Global Circulation Models

WP4 Martian trace gases, dust and clouds
analyse space data to retrieve information on trace gases and aerosols
Major results:
* Select space data to derive trace gases and dust, to test different dust parameters and to validate our results
* Sensitivity study on the the different dust and clouds parameters on the dust and trace gases retrieval from NOMAD data
* Implementation of new dust and clouds parameterizations in the retrieval codes
* Investigate how to include the treatment of the polarisation using VLIDORT

WP5. Global modelling and climatologies
build on the current state-of-the-art in General Circulation Models (GCMs) and to provide atmospheric states to research groups through climatologies
Major results:
* increased the representation of ice particle size in the GCM in preparation for the inclusion of the detailed microphysical code for dust and water ice particles
* new optical properties computed for different particle sizes and implemented in radiative transfer calculation
* new simulations applied to case of dust storm 2018
* updated climatologies provided for input to ASIMUT

WP6. Dissemination and Exploitation of results
disseminate the knowledge and outcomes generated by ROADMAP, involving and reaching the scientific and education community, as well as the general public
Major results:
* roadmap website created
* the first animation (explaining the role of dust in the martian atmosphere) has been made public
* interviews of researchers involved in the project available to the public
For the first time, RoadMap has characterized martian dust samples from the laboratory to their use for space data analysis, improving the description of physical and radiative processes in which dust and clouds are involved.
Establishing links between different communities (Laboratory - Modeling - data analysis)
Impact on the general public:
* interviews of researchers at different moment in their career to promote science in general, space science in particular
* animations to introduce science done with RoadMap addressed to a young public or non-scientific public
Logo of the RoadMap project