Modifying an ice nucleation parameterization to include feldspar dust in E3SM

Monday, December 10, 2018 - 08:00
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Dust aerosols play a critical role in mixed-phase clouds by lowering the energy barrier for ice nucleation, thus allowing nucleation to take place at warmer temperatures. Feldspar dust accounts for 11% of dust mass and potassium feldspar initiates ice nucleation approximately 8.5°C before any of the other major mineral dust types (e.g. quartz, mica, kaolinite, calcite) (Atkinson et al., 2013). In this study we use the Department of Energy’s climate model, Energy Exascale Earth System Model (E3SM) version 1, to increase the activation of ice nucleation on feldspar dust. The goal of this study is to identify whether ice nucleation is better represented in E3SM when accounting for the variation in nucleation temperature due to mineral type. At present E3SM treats all dust as one species. In this study, a feldspar dust tracer is added into the Modal Aerosol Model version 4 (MAM4) and the DeMott et al. (2010) parameterization is modified to increase ice nucleation on feldspar dust based on temperature. The surface distribution of feldspar dust is incorporated using the arid soils map from the GMINER30 database (Nickovik et al., 2012). The simulations are run for 5-years at approximately 1 degree resolution. The simulations are compared with airborne and ground-based observations of dust distribution and ice nucleation. Preliminary results suggest that global annual averages in liquid and ice water path, shortwave and longwave cloud forcing, and cloud total change relatively little in response to the change in ice nucleation parameterization. However, there are large regional changes, for instance in northern Africa, cloud ice water path increases by >50%.

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