AMASDU

The objective of the AMASDU project was the development of 4D products related to global mapping of aerosols, with improvements to data assimilation models.

The approach followed for the production of these global aerosol maps was a 4D variational data assimilation method, complementary to the low-level cartography approach experimented during the DUP DAMS2P project (Development of Global Aerosol Mapping from Satellites level-2 Products). The 4D variational data assimilation method is based on a numerical atmosphere model that propagates the aerosol particles in a dynamically consistent way. The model dynamics are based on ECMWF wind analyses.

The implementation was based on different modules:

• the atmospheric model describing the evolution of the atmosphere's state forward in time. It includes a choice of dynamics, photo-chemistry, and aerosol microphysics modules, according to the assimilation needs
• the adjoint model, including techniques for automatic differentiation of the atmosphere model. When calculated backwards in time, it gives the gradient of the discrepancy between model calculated values and observations with respect to the initial state conditions.
• an optimization (iteration) module, tuned for large-scale problems, which minimizes the discrepancy between calculated and observed values.