Objectives

  • Lifting model
  • Aggregation model
  • Dust & Clouds Radiative model
  • Aerosol micro-physical model

Lead / Participants

UDE ( BIRA-IASB, AU, IAA)

The RoadMap project will develop a series of tools and new methods to address different atmospheric processes involving aerosols.

 

Science

Light scattering modelling

In RoadMap the unique experimental database of scattering matrices of Martian dust analogues obtained in the lab will be used to check the validity of state-of-the-art numerical techniques based on simplified model particles to reproduce the scattering behaviour of realistic polydisperse irregular particles. In particular, spheroidal/ellipsoidal dust models can be computed with the T-matrix approach, aggregates consisting of spherical monomers with the T-matrix approach, spherical aggregates with the multiple sphere T-matrix method, and more complicated shapes with volume-integral-equation methods such as Discrete Dipole Approximation (DDA).

Dust lifting and transport model

To lift grains from the ground by wind requires a minimum (threshold) wind speed. This threshold depends on the soil and gravity. Particle sizes and cohesion are major ingredients. A number of equations exist for threshold conditions. However, they include material parameters. Therefore, as we work out realistic Martian analogues these values have to be adapted.

Dust evolution model

The non-volatile dust will evolve while being suspended in the atmosphere. Grains regularly grow to aggregates through collisions. With grains being charged or reacting to atmospheric electric fields by dielectrophoresis, the cross sections and way they form aggregates will be modified. Depending on the aggregation, the sedimentation speed and further aggregation will change. Change in aggregates structure will also come along with cloud formation. As water ice nucleates on grains and resublimates later, aggregates can break up or become more compact. The atmosphere will eventually purge itself from large particles by sedimentation. However, this is strongly depending on the morphology of the aggregates as large aggregates with very low fractal dimension can behave like individual grains with respect to gas drag.

Micro-physical model for aerosols

The process of cloud formation occurs on a short time scale and a physical scale much smaller than a typical grid box of a three-dimensional global model (which is on the order of ~200 km across) so the effects on the grid scale fields must be estimated. Sensitivity studies will be performed with the one-dimensional version of the new micro-physical model in preparation for its inclusion in the three-dimensional global model. For example, the number of size bins representing the aerosols will be optimized to balance accuracy with computation time. The routine will use input from lab experiments’ results to improve particles properties such as their shape and radiative properties.

 

Expected results and Impact