Modeled response in radiative properties of isolated shallow convective clouds due to perturbations in meteorological state variables and atmospheric aerosol loading
(English)Manuscript (preprint) (Other academic)
The aim of the present study is to estimate the range of variability in observational data of meteorological variables permitted to determine a clear and unambiguous signal in cloud fraction and cloud albedo due to changes in aerosol concentrations. Three different cases of tropical shallow convection have been simulated using a two-dimensional cloud resolving model with aerosol-cloud interactions. For each case, 30 different small perturbations were added to the initial meteorological profiles of zonal wind, potential temperature and specific humidity. For each meteorological per- turbation an additional 14 simulations were performed with different boundary layer accumulation mode aerosol concentrations ranging from clean (50 cm-3) to polluted (1350 cm-3) conditions. A total of 5040 simulations were performed to elucidate the impact of aerosols on the simulated cloud fraction and cloud albedo and to compare this to the corresponding impact to the influence of small meteorological perturbations. For the simulated cases, we find that for cloud fraction, the aerosol signal is in general much weaker than the change due to small changes in meteorology. This was especially true for parameters that influence the relative humidity of the environment, i.e. tempera- ture and specific humidity. For cloud albedo, the aerosol signal surpasses that of the relatively small meteorological perturbations. We find up to 40% difference in cloud albedo going from clean to polluted conditions. The corresponding maximum change due to the meteorological perturbations was only 14%. We conclude that for the simulated shallow convective clouds, isolating an aerosol effect on cloud fraction is not possible if using meteorological analysis data containing errors of the same order of magnitude as the imposed meteorological perturbations. However, the meteorological constraints may be sufficient to isolate an aerosol effect on cloud albedo.
Meteorology and Atmospheric Sciences
Research subject Atmospheric Sciences and Oceanography
IdentifiersURN: urn:nbn:se:su:diva-62821OAI: oai:DiVA.org:su-62821DiVA: diva2:445051