Adjoint analysis of ice crystal sensitivity to heterogeneous nucleation spectrum in CAM 5

Adjoint analysis of ice crystal sensitivity to heterogeneous nucleation spectrum in the CAM 5

Sylvia Sullivan [1], Benjamin Sheyko [1], and Athanasios Nenes [1,2] 1 Georgia Institute of Technology, School of Chemical and Biomolecular Engineering 2 Georgia Institute of Technology, School of Earth and Atmospheric Sciences

The adjoint model of the 2009 Barahona and Nenes ice cloud parameterization (ABN09) is used to understand cirrus crystal number sensitivity to updraft velocity; temperature; and sulfate, black carbon, and dust number and size in the Community Atmosphere Model version 5. We focus on differences in these sensitivities caused by different heterogeneous ice nucleation spectra. A default spectrum, Meyers et al. 1992, contains only supersaturation dependence and is used to evaluate the importance of including aerosol profile in the nucleation spectrum. Crystal number sensitivities are also calculated with the Phillips et al. 2008 and, for the first time, updated Phillips et al. 2013 spectra in the ABN09 framework. These two empirical spectra depend strongly on aerosol profile, and several input parameters and correlations change value or form between the two. Changes in their sensitivity, then, show where the description of various ice-nucleating aerosol groups can be most influential. In particular, we investigate the importance of aerosol surface area available for nucleation, classification of organics, and the functional representation of black carbon. Attribution plots point to the geographical regions where the results for each of these factors may have the largest impact. This attribution analysis also indicates whether variability in output crystal number comes from inherent parameterization biases or from natural aerosol fluctuations.