Aerosol indirect effects on glaciated clouds. Part I: Model description

Abstract

Various improvements were made to a state‐of‐the‐art aerosol–cloud model and comparison of the model results with observations from field campaigns was performed. The strength of this aerosol–cloud model is in its ability to explicitly resolve all the known modes of heterogeneous cloud droplet activation and ice crystal nucleation. The model links cloud particle activation with the aerosol loading and chemistry of seven different aerosol species. These improvements to the model resulted in more accurate prediction especially of droplet and ice crystal number concentrations in the upper troposphere and enabled the model to directly sift the aerosol indirect effects based on the chemistry and concentration of the aerosols. In addition, continental and maritime cases were simulated for the purpose of validating the aerosol–cloud model and for investigating the critical microphysical and dynamical mechanisms of aerosol indirect effects from anthropogenic solute and solid aerosols, focusing mainly on glaciated clouds. The simulations showed that increased solute aerosols reduced cloud particle sizes by about 5 μm and inhibited warm rain processes. Cloud fractions and their optical thicknesses were increased quite substantially in both cases. Although liquid mixing ratios were boosted, there was however a substantial reduction of ice mixing ratios in the upper troposphere owing to the increase in snow production aloft. These results are detailed in the subsequent parts of this study.

Aerosol indirect effects on glaciated clouds. Part 2: Sensitivity tests using solute aerosols

“…Hence, this study proposes to contribute to the knowledge of aerosol–cloud interactions (aerosol indirect effects) on glaciated clouds by way of sensitivity tests, using a state‐of‐the‐art aerosol–cloud model (Phillips et al , , ; Kudzotsa, ; Kudzotsa et al ) that encapsulates the tested and robust heterogeneous ice nucleation scheme of Phillips et al (, ), which treats all four known modes of heterogeneous ice nucleation (Diehl et al ; Diehl et al ; Hoppel et al ; Dymarska et al ). The details of this model have been described in full in Part 1 of this series of articles (Kudzotsa et al ).…”

“…The control run for the simulated case was specified as described in Kudzotsa et al () and was simulated using present‐day aerosol scenarios and thermodynamic conditions for model forcing. In order to specify the pre‐industrial aerosol fields, the work of Takemura () on the global distribution of atmospheric aerosols from the pre‐industrial era (1850) to future projections (2100) (using global models) was used.…”

“…This is because there are large uncertainties in the measurements and knowledge of ice nucleating aerosols (Cziczo et al, 2004;DeMott et al, 2011) and also in the mechanisms of ice nucleation at different temperatures and humidities (Meyers et al, 1992;Phillips et al, 2008;Eidhammer et al, 2009). Hence, this study proposes to contribute to the knowledge of aerosol-cloud interactions (aerosol indirect effects) on glaciated clouds by way of sensitivity tests, using a state-of-the-art aerosol-cloud model (Phillips et al, 2007(Phillips et al, , 2008(Phillips et al, , 2009Kudzotsa, 2013;Kudzotsa et al, 2016) that encapsulates the tested and robust heterogeneous ice nucleation scheme of Phillips et al (2008Phillips et al ( , 2013, which treats all four known modes of heterogeneous ice nucleation (Diehl et al, 2001(Diehl et al, , 2002Hoppel et al, 2002;Dymarska et al, 2006). The details of this model have been described in full in Part 1 of this series of articles (Kudzotsa et al, 2016).…”

Effects of solid aerosols on partially glaciated clouds

“…)) and they fell satisfactorily within one standard deviation from the observed average values as shown in Kudzotsa et al. ().…”

“…Part of the methodology and some sensitivity tests used here to assess solid aerosol indirect effects are similar to those used in another article by Kudzotsa et al. (), therefore in this section we provide a brief description of the model and methodology to allow a smooth flow of ideas. However, the reader is refereed to those two earlier articles for a detailed description of the model, model validation, and sensitivity tests.…”