## 2 Experiments
### Observational Data for the Evaluation of Model Performances  
Various sources of data and derived products are used to evaluate the performances of the model for the March 2014 period; they are briefly described below. * CALIPSO and CloudSat, launched in 2006 as part of NASA's A-train satellite constellation, provide detailed information on cloud and aerosol vertical profiles from tropics to the poles. Cloud vertical profiles are derived from Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) [78]. Here, we use the V4.10 dataset [79], cross section of the atmosphere provides various categories separating mineral dust from anthropogenic pollution. The list of selected orbits is given in Figure 2.  
Figure 1: Erodibility map used in CHIMERE for this study (with black and white topographic background). * MODIS (Moderate Resolution Imaging Spectroradiometer) is a key instrument aboard the Terra (originally known as EOS AM-1) and Aqua (originally known as EOS PM-1) satellites. Terra's orbit around the Earth is timed so that it passes from north to south across the equator in the morning, while Aqua passes south to north over the equator in the afternoon. Terra MODIS and Aqua MODIS are viewing the entire Earth's surface every 1-2 days, acquiring data in 36 spectral bands, or groups of wavelengths. The MODIS Aerosol Product monitors the ambient aerosol optical thickness over the oceans globally and over the continents. Furthermore, the aerosol size distribution is derived over the oceans, and the aerosol type is derived over the continents. \"Fine\" aerosols (anthropogenic/pollution) and \"course\" aerosols (natural particles; e.g., dust) are also derived [80, 81]. MODIS products are downloaded from the Worldview tool developed by NASA accessible at [[https://worldview.earthdata.nasa.gov/](https://worldview.earthdata.nasa.gov/)]([https://worldview.earthdata.nasa.gov/](https://worldview.earthdata.nasa.gov/)). In this paper, the merged Dark Target/Deep Blue Aerosol Optical Depth product will be used. It provides a more global, synoptic view of aerosol optical depth over land and ocean. This layer is created from three algorithms: two \"Dark Target\" (DT) algorithms for retrieving: (1) over ocean (dark in visible and longer wavelengths); and (2) over vegetated/dark-soiled land (dark in the visible); and the Deep Blue (DB) algorithm, originally developed for retrieving (3) over desert/arid land (bright in the visible wavelengths). Which algorithm is used for a particular location on the Earth depends on its surface cover. * The MISR (Multi-angle Imaging SpectroRadiometer) Aerosol Optical Depth Average layer product is also used. This instrument on board Terra displays the temporal averages of all aerosol optical depths calculated from radiances acquired from the green band (555 nm) of MISR's cameras as an average value for March 2014. This instrument is aboard the Terra satellite. * Atmospheric composition data from the US IMPROVE network are also available with PM\({}_{2.5}\), PM\({}_{10}\) and Soil PM concentrations based on calcium measurements [82]. Daily data are available every three days and available at [[http://vista.cira.colostate.edu/Improve/improve-data/](http://vista.cira.colostate.edu/Improve/improve-data/)]([http://vista.cira.colostate.edu/Improve/improve-data/](http://vista.cira.colostate.edu/Improve/improve-data/)). Figure 2: List of CALIPSO passes used in this study (with topographic background); all the comparisons with CHIMERE are provided in Supplementary Materials (Figures S1–S5).