247 Susceptibility and Resilience of Aerosol-Cloud-Precipitation Interactions in 2D Orographic Mixed-Phase Clouds

Wednesday, 9 July 2014
Franziska Glassmeier, ETH, Zurich, Switzerland; and N. Herger, F. Ramelli, and U. Lohmann

The notion of clouds as resilient or buffered systems implies that adjustment processes unaccounted for in climate simulations may lead to an overestimation of the effective radiative forcing due to aerosol-cloud interactions, i.e. cloud lifetime effects. In this contribution, we study the importance of microphysical adjustment processes in response to anthropogenic aerosols in orographic mixed-phase clouds. Our methods can be extended to other cloud regimes as well as dynamical and thermodynamical adjustments.

For our simulations, we use the regional atmospheric model COSMO-ART in a 2D setup with an idealized mountain. To capture major processes from aerosol emission to precipitation, the model is coupled to a modal aerosol scheme and includes aerosol activation and heterogeneous freezing as well as two-moment cold and warm cloud microphysics.

Our analysis is based on quantifying interaction strength by susceptibilities, i.e. relative sensitivities d ln(Y) / d ln(X), where Y is the response to a perturbation X. We describe how to decompose susceptibilities into the contributions of the parametrization and of the adjustment processes. Using this method we compare the importance of adjustment processes in response to aerosol perturbations for the ice-phase and warm-phase pathways of precipitation formation. By varying the temperature and chemical composition of the aerosol we can control the relative contributions of these two pathways. This allows us to explore the degree of resilience resulting from the interplay of warm and cold aerosol-cloud-precipitation interactions in mixed-phase clouds.

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