Section: Software

Polyphemus

Participants : Vivien Mallet, Anne Tilloy.

Polyphemus (see the web site http://cerea.enpc.fr/polyphemus/ ) is a modeling system for air quality. As such, it is designed to yield up-to-date simulations in a reliable framework: data assimilation, ensemble forecast and daily forecasts. Its completeness makes it suitable for use in many applications: photochemistry, aerosols, radionuclides, etc.  It is able to handle simulations from  local to continental scales, with several physical models. It is divided into three main parts:

• libraries that gather data processing tools (SeldonData), physical parameterizations (AtmoData) and postprocessing abilities (AtmoPy);

• programs for physical preprocessing and chemistry-transport models (Polair3D, Castor, two Gaussian models, a Lagrangian model);

• drivers on top of the models in order to implement advanced simulation methods such as data assimilation algorithms.

Figure 1 depicts a typical result produced by Polyphemus. Clime is involved in the overall design of the system and in the development of advanced methods in model coupling, data assimilation and ensemble forecast (through drivers and post-processing). 

In 2012, Polyphemus received several physical developments on secondary organic aerosols, modeling of pollution due to traffic emissions and coupling of local and regional scale models. Further integration with the data assimilation library Verdandi has been carried out. A Python interface to the Eulerian model Polair3D has been introduced.

Figure 1. Map of the relative standard deviation (or spread, %) of an ensemble built with Polyphemus (ozone simulations, $\mu g{m}^{-3}$). The standard deviations are averaged over the summer of 2001. They provide an estimation of the simulation uncertainties.