Abstract
The direct radiative effect of aerosols is taken into account in many limited-area numerical weather prediction models using wavelength-dependent aerosol optical depths of a range of aerosol species. We studied the impact of aerosol distribution and optical properties on radiative transfer, based on climatological and more realistic near real-time aerosol data. Sensitivity tests were carried out using the single-column version of the ALADIN-HIRLAM numerical weather prediction system, set up to use the HLRADIA simple broadband radiation scheme. The tests were restricted to clear-sky cases to avoid the complication of cloud–radiation–aerosol interactions. The largest differences in radiative fluxes and heating rates were found to be due to different aerosol loads. When the loads are large, the radiative fluxes and heating rates are sensitive to the aerosol inherent optical properties and the vertical distribution of the aerosol species. In such cases, regional weather models should use external real-time aerosol data for radiation parametrizations. Impacts of aerosols on shortwave radiation dominate longwave impacts. Sensitivity experiments indicated the important effects of highly absorbing black carbon aerosols and strongly scattering desert dust.
Highlights
Aerosols are tiny solid and liquid particles suspended in the air
In subsequent sections we show the results of the tests done using the HLRADIA radiation scheme for the detailed study of the impact of different climatological and n.r.t. aerosol input data and inherent optical properties (IOPs)
We suggest improvements to the aerosol radiative transfer parametrizations in the ALADIN-HIRLAM numerical weather prediction (NWP) system
Summary
Aerosols are tiny solid and liquid particles suspended in the air They cause direct radiative forcing through scattering and absorbing shortwave (SW) and longwave (LW) radiation in the atmosphere. They alter cloud formation and precipitation efficiency by increasing droplet and ice particle concentrations. The quantification of aerosol radiative forcing is more complex than that for greenhouse gases because aerosol mass and particle concentrations are highly variable in space and time. This is mainly due to the shorter atmospheric lifetime of aerosols. Spatial and temporal information on the physical and radiative properties of aerosols is required such as size distributions, dependence on relative humidity, refractive index and solubility of the particles
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