# Large-Scale Modeling of Absorbing Aerosols and Their Semi-Direct Effects
## 3 Results
### Radiative Effects  
#### 3.2.1 Impacts on Atmospheric Heating Rates  
The impact of aerosol absorption on atmospheric dynamics and cloud cover is a consequence of changes in atmospheric heating rates (HR) by the presence of aerosols. Heating rate differences due to the presence of an absorbing aerosols are computed as differences between the heating rates of the model, including all aerosol species and the results of a simulation not including this aerosol type. The instantaneous heating rate changes were computed by double calls to the radiation routine to diagnose the heating rates without influencing the atmospheric conditions driven by the aerosol forcing, as done for diagnosing the instantaneous radiative forcing. Figure 3 shows the vertical distributions of instantaneous heating rate changes from dust and BC aerosol. The results are computed as differences of the simulated heating rates from experiments BASE and noDust and noBC, respectively. Figure 2: Annual average of the absorbing aerosol optical depth (AAOD) distribution. (**Top panel**) OMI AAOD satellite product at 500 nm, averaged for 2004 to 2010. (**Middle panel**) Eight-year annual average BASE simulation results for AAOD at 550 nm. (**Bottom panel**) Eight-year annual average GFAS simulation results for AAOD at 550 nm. Shown are zonal means for the individual months of July and January, representing winter and summer conditions. For July conditions the HR maxima for BC occur near the Equator and can reach values of 0.1 K/day in the zonal mean. Local maximum heating rate changes due to black carbon heating reach values up to 1.3 K/day, which is lower compared to, e.g., the locally evaluated HR of 7-8 K/day by [PERSON] et al. (2012) for conditions in the Pearl River delta in China. This may be a consequence of the coarse model resolution, which may cause a stronger mixing and, thus, stronger dilution of boundary layer pollution in the model compared to the observation. BC heating rates near the equator are enhanced by biomass burning aerosols, and in mid-latitudes by aerosols from industrial emissions. BC is mixed to heights above 5 km into the free troposphere in the northern mid-latitudes due to large injection heights for biomass burning smoke. HR changes due to mineral dust are of comparable magnitude in the zonal mean near the ground, reaching zonal mean values of 0.06 K/day due to absorption by dust over the Sahara. In summer the heating rate changes due to the presence of dust impact latitudes from 20-30\({}^{\circ}\) N to heights up to 500 hPa, which reflects the dust transport into and within the Saharan Air Layer (SAL). Monthly maximum HR changes were as high as 1.3 K/day for dust aerosol. This agrees quite well with the early study by [PERSON] and [PERSON] (2013), who estimate a heating rate change by dust of 1 K/day for the SAL over the Atlantic. Some negative values of about 0.01 K/day in the zonal mean occurred here as well in the sinking branch of the Hadley circulation at 30\({}^{\circ}\) N. This cooling is due to the thermal forcing effect as dust due to its particle size is both absorbing and emitting longwave radiation in the thermal infrared part of the spectrum. The same is the case for January conditions, where the effect of BC reaches 500 hPa near the equator in the biomass burning-influenced region, but remains at much lower altitudes in the northern mid-latitudes. BC from industrial emissions in winter conditions does not frequently reach the free troposphere. For dust the atmospheric cooling is more pronounced in January than in July, reaching a minimum of \(-0.02\) K/day over the Saharan region. Considering only solar radiation, heating rates are positive overall for dust and BC aerosol forgings. Solar heating by dust reaches up to 1.1 K/day in January. Overall, due to partial cancellation of both heating and cooling effects by dust aerosols the overall radiative effects are not as obvious compared to the overall increasing in atmospheric HR due to the presence of BC aerosol.