# Large-Scale Modeling of Absorbing Aerosols and Their Semi-Direct Effects
## 3 Results
### Regional Effects  
Global model studies of the DRE and SDE show the range of forcings and responses between different models is large, and in particular the effect of the absorbing aerosol is difficult to assess since it also depends on the ability of the model to simulate cloud processes in a realistic way [2; 3]. Additionally, the coarse model resolution may be problematic when considering aerosol transport and cloud interaction processes. Regional model studies that have higher spatiotemporal resolution and realistic meteorology are on the other hand limited to individual events and thus it is difficult to obtain general conclusions from such simulations. As example for earlier model studies and to test if some agreement can be found in the global model results we compare the results by ECHAM-HAM with earlier results by [PERSON] et al. [19] and [PERSON] et al. [21] who had utilized the COSMO-MUSCAT regional aerosol-transport model with radiatively interactive aerosol. Here we test if similarities in the results of the two models, the regional model COSMO-MUSCAT and the global aerosol-climate model ECHAM6-HAM2 (that not only differ in their parameterizations of aerosol processes, but also operate on very different spatial and temporal scales) obtain at least qualitatively similar results for the responses to the absorbing aerosols. Figure 7: Scatterplot of model results of annual averaged BC TOA SDE in relation to cloud cover changes for the differences of the simulations noDUST and noABS. Results from model grid cells that are statistically significant at 95% levels are plotted in dark blue, results from grid cells with results with statistical significance below 95% are plotted in light blue. [PERSON] et al. (2006) investigated the role of anthropogenic absorbing aerosol in Europe for a period in July 2006, for which the aerosol distribution had been thoroughly tested. A positive semi-direct effect (+2.4 Wm\({}^{-2}\)) and reduction in cloud cover (1%) were simulated for the average of the area average due to absorbing aerosol. Locally, SDE as high as +6 Wm\({}^{-2}\) and cloud reduction up to 4% was simulated with the regional model. The difference for the eight-year July average for the BASE and noBC simulations from the global model simulations are compared to the regional results. Overall in the European region the cloud cover in the month of July is reduced in central Europe (Figure 8a), with reductions between 5 and 10%. This is similar to the regional model result in the study by [PERSON] et al. (2006), even though the model setups were very different the specific meteorological conditions for 2006 that were simulated with the regional model are compared to a multi-year average in the global model. A second example for a regional study of the radiative feedback of aerosol absorption on atmospheric dynamics is the study including the radiative dust and biomass burning smoke during the SAMUM2 experiment in 2008. [PERSON] et al. (2011) simulated the atmospheric adjustment due to the dust and biomass smoke forcing in the Sahel and tropical Atlantic for the conditions during the field study with the COSMO-MUSCAT regional model. They found that in particular the absorption by biomass smoke led to an enhancement of the Hadley circulation and convergence along the Guinea coast. Dust export was reduced from the Sahara off the coast to the tropical Atlantic but enhanced over the Sahel and dust transport enhanced equator-wards. Differences in the dust AOD for the ECHAM6-HAM2 simulations BASE and noBC (Figure 8b) show similar qualitative changes in dust AOD resulting from the radiative effect of BC, with a reduction in Saharan dust and increase in dust from the Sahel region in the climatological mean for the month February. The dust AOD is increased by about 0.05 in the Sahel and the decreased in the Saharan desert by 0.2. These resulting changes are which is actually close to the results that [PERSON] et al. (2011) simulated with the regional model.